Converting early gas MH to Duramax? Possible?

[BigRabbitMan]

I have a '70's era motor home that weighs about 15,000 lbs. and with a tow vehicle gcvw could get to 18,000 lbs. I am going to replace the existing power train with a modern power train. At this point I feel my options are either stay with gas and convert to the GM 8.1L Vortec with the Allison 1000/2000 transmission or convert to the LLY or LBZ with a matched Allison 1000. Given the natural low rpm torque profiles and better performance at altitude of tubo diesel, I would prefer to go to diesel even though it will be more complicated. It also is easier to avoid fuel quality problems in Central America where I will be traveling at some point with diesel vs gas.

With the existing gearing of my unit, in 5th the engine will be turning about 2300-2400 rpm at 65 mph. This seems a little high to me for a cruising rpm for a diesel engine. If the new 6 speed Allison and matched engine can be found, it would turn 1800-1900 rpm at 65mph. That seems better to me as the engine is just turning fewer rpm with less wear and should/would get better fuel economy.

Now the questions:

Is my weight too high as a constant weight/load? What are the different characteristics of the LLY/LBZ at those two rpm levels? What are the torque/economy trade offs? Is the LLY/LBZ happy at the higher rpm as normal rpm? Where can I find a downloadable copy of the torque curves of the LLY and the LBZ?

The weight of the 6.6L is close to the weight of the existing engine and I will completely redesign the cooling system. Others that have reviewed my plans are about evenly divided between thinking it is a great idea to move to one of these modern power/transmission combinations to thinking I am out of my mind. That is probably true, but I won't let it get in the way!

To make the transition, I would purchase a used engine/trany with engine and trany wiring harness and computers and anything else needed. My existing engine had a water pump failure and overheated to the point that major engine damage resulted so now is the time to make a change if I am ever going to do it. The coach is a 1976 FMC.

I thank all you knowledgable Duramax experts for your learned advise.

[Dakster]

I can't help with the intricacies of conversion. Having driven both GAS and DIESEL Motorhomes. I vote for the diesel MH. Since you are upgrading from a 70's era gas motor to a current gas/diesel motor I would be shocked if you didn't get alot more power and better mileage then you are now. Diesel should last a lot longer they are better designed for moving lots of weight. I like the quiet diesel (onan/cummins) generators - again lasts longer and uses a little less fuel per watt.

If money is an issue, the gas motor should cost a lot less to install and should be taken into consideration. Unless you have a friend willing to donate his used DMAX motor...

However, I know many a diesel RV that get in 5-6 MPG range, so I wouldn't expect great fuel mileage numbers. Granted these are 40' RV's that empty weigh 23k and towing a car.

Not that I believe either of these motors are the holly grail of RV motors. But have you researched the most common motors found in large RV's? (Cat / Cummins) I would want all options on the table to pick thru, before I made my choice. Especially since just PARTWISE you are looking at spending some serious cash.

[BigRabbitMan]

Here is a link to a picture of the coach. It is a rear engined unit and since the coach physical structure and weight balance was designed for the weight of the existing 440-I, I am unable to go to a larger power plant without major modifications to the frameing, etc. of the coach. Others in years past have gone to the 1560 lb. 8.2L turbo Detroit Diesel, but had to do much more structural work due to the weight than I am willing to do. That increase in rear end weight also affects the drivability and I like being able to take curves at 10 mph over the posted speed. It is 4 wheel independent suspension with a transverse leaf spring in the front and independent, trailing arm, torsion bar suspension in the rear.


http://inlinethumb15.webshots.com/3662/2174711060012124553S600x600Q85.jpg

This a 29' coach so it is much lighter than most diesel powered coaches. I know that both gas or diesel will perform well. The 440 would take it up 6% grades at 55 mph. Either of the options will add significant HP, but the higher torque of the diesel at lower rpm will significanly increase the drivability and have other benefits as well. The torque to lbs. ratio of the Duramax is the perfect match IF it can be done one stop short of Fort Knox. I don't want to go to the Vortec engine and then later learn how well the Duramax would have worked and have "Wish I would have's".

I expect a conversion to a Duramax to cost 50% more than to a 8.1L Vortec, but the difference in lower rpm torque and other factors would be worth it to me. Either one will be a time consuming job to get all the harness installed and systems working properly. What ever I do, once the conversion is done it can't be redone to try the other way so this is the one opprotunity to get it right.

My MAJOR question is what happens/will happen if the Allison 5 spd is used and the coach is geared to cruise at the 2300-2400 rpm range. What will this do to a LLY? Nothing? Cause a cooling problem? Burn fuel like crazy?

At 15,000 lbs. what milage could I expect under cruise control with that weight and rpm?

At that weight and rpm, what degree grade would trigger a downshift from 5th to 4th? 2% grade? 3% grade? 4% grade?

A 10,000 lb. trailer plus 3500 dually will weigh as much or more than my coach. In reading posts here, it appears that there are a number of people that run this type of rig on a regular or contunuous basis. Their experiences should parallel what I could expect if I make the conversion. What is the normal rpm of a 2500/3500 with the Allison 5 spd on cruise control at 65 mph?

I am now focusing on the LLY with the 5 spd as the 6 spd is just too new with too few of numbers on the road to be showing up with salvageable engine/tranys in salvage yards yet. Everyone is still driving carefully with the new trucks!

If the LLY with the Allison 5 spd appears to be a good fit at the gearing described above, then I can move on to the other issues such as RELATIVE cost, technical aspects, availability, etc., etc..

This forum is where the experience and knowledge of how a Duramax operates and performs is located. That is why I am asking these questions here and not in an RV forum where I would just get speculation. I have been speculating too much on my own.! Here are the people that actually drive them!!

I appreaciate everyone's assistance,

[Mark Rinker]

Have you considered swapping in the drivetrain from a 6.5TD motorhome?

[BigRabbitMan]

Mark,

No I haven't and won't for a couple of reasons. The first is that if I am going to go through the tremendous amount of work that it will take to put any diesel into my coach, I want to be as current in the technology as possible. The second is the constrants of space and weight to power issues with my coach. I am not wanting to diesel the coach just to be "dieseling it". I am looking at some specific attributes that the Duramax has that are not there with earlier engines or other brands.

If I can't get any answers to the questions I posed above, I will go with the 8.1L Vortec. It's an easier conversion. I am not quite sure why some relatively straight forward questions such as normal rpm at 65 mph are going unanswered.

Thank you for your interest,

[a5150nut]

IIRC, the Allison 5 speed of certain varieties has an aftermarket conversion to make it 6 speed double over. Might check with John Kennedy on that. Be patient, some one will comew along with your answers. In the mean time, gear ratio and tire size might help. I remember a link arround here to a conversion table to determine rpm at a a given speed.

Good luck and happy motoring.

A quick search and I found 1 Gear/RPM Calculator (http://www.700r4.com/speedoCalc/rpmcalc.shtml)

Hope this helps. If not there was another one on 4x4 site.

[DmaxMaverick]

......I am not quite sure why some relatively straight forward questions such as normal rpm at 65 mph are going unanswered.

Thank you for your interest,



It's not straight forward. Your MH will have a drive ratio unique the the MH. Very different than the vast majority discussed here. Your RPMs will be the same in direct (Allison 4th gear), regardless of the tranny. The 5/6 speed Allisons will have an OD of .71 in 5th, and .61 in 6th. Just do some math (or ask for help with it) and compare it to what you have. Unless you plan on changing the tire size and/or drive ratio, it will be the same, with an addition of OD(s). A 6 speed may not be the best answer if you have no OD now. If you have a 70's era auto tranny (TH400?), it will have a direct final gear. Adding any OD will be a bonus, and a lockup converter won't hurt, either. With the weight you are dealing with, a double OD won't help unless you have a deep enough final drive ratio.

[Dakster]

Nice looking coach. I can tell you take really good care of it and have alot of modern conviences added... To your fuel mileage question, I will sum it up based on what the RV salesman told me. "No one buys these things for the mileage they get." Gas or Diesel I doubt you'll break 10mpg. based on your description of your driving habits. This is of course, my opinion, and is based upon my unique experiences.

BTW, I drive RV's between 75-80 mph too... So don't take the comment as a flame.

[Duramaster]

I don't know much about "repowering" M/H but I can say from experience STAY AWAY FROM THE 6.5 TURBO DIESEL! :D The DMAX or the 8.1 is the best way to go!!

[JeepSJ]

Wasn't there an article on here a while ago about an older FMC motorhome that was converted to a DMax? That one was also rear engine.

[BigRabbitMan]

Yes, in 2004 and it is no longer online. I would be more interested in finding out who the builder/owner was/is to see what the long term report has to say than how he did the conversion.

I see the conversion just as a tedious process once all the needed hardware is identified and obtained. Every conversion has differences that reflect the ideas and preferences of the person doing the conversion. I would hope to do a good job of documenting what I do so that others who are wanting to prolong the life of and moderize their FMC will have a path to follow. Of the 1050 of them built from 1972-76, it is estimated that 700-800 of them are still on the road.

My coach (as all of them) originally had the Chrysler 440-I (Industrial or Marine version) and a Loadflite 3 spd transmission. I previously swapped the transmission to an Allison 545 and replaced the carburator with an Edelbrock MPI fuel injection system so I am no stranger to conversion or modification. Here is a picture that shows a different modification I did. That is a satellite internet dish deployed while we stopped at a beach in southern California.
http://inlinethumb45.webshots.com/6316/2995790510012124553S600x600Q85.jpg (http://travel.webshots.com/photo/2995790510012124553SfINaS)

With that engine having toasted due to water pump failure, now is the time to look at going to the next level. I may swap in a used 440 that I am aware of to be able to use the coach while I am assembling and designing the conversion over to the Duramax and modern Allison.

Thank you for your assistance and interest,

[BigRabbitMan]

BTW, I drive RV's between 75-80 mph too... So don't take the comment as a flame.

A double overdrive would make for sweet traveling at 80 mph!!!!!

[hogmotors]

I believe that a stock DMAX w/3.73 gear & stock 2.45 75R16's runs about 2400 @ 75mph. My 99 sub 6.5L ran that & I expect the DMAX to do about the same when it hits the road since I didn't change gears.

[Dakster]

BigRabbitMan,

Have you made any decisions or started on the project?

[journeyman]

My dad has the 2900 R (1974) and quite possibly I will be inheriting it someday.

We have the 454/4L80e in it and got 8 MPG with the TH400 and yet to get enough driving data with the 4L80e.

I also would like to consider the LMM/Allison 6 speed. Weight on the engine is comparable. 1000 should be similar to the 545.

Jim Black told me that vibration was a problem with diesels in the 2900R and it would need significant body (structural) strengthening that he does. the Duramax may not have those vibration issues (that would be my hope).

I am impressed with the 454, and possibly will keep it in favor of diesel... But may inject it to improve efficiency

[journeyman]

Specifics:

The Marine Ind. 440: Weight: Long block as shipped: 670#
With accessories and manifolds it will easily be over 700

The Duramax (when introduced) was touted at 835 Lbs.

165 Lbs heavier seems like a safe ball park figure for weight.
Moving the exhaust (massive muffler) out of the engine bay will save you another good bit of weight.

[BigRabbitMan]

My dad has the 2900 R (1974) and quite possibly I will be inheriting it someday.

Jim Black told me that vibration was a problem with diesels in the 2900R and it would need significant body (structural) strengthening that he does. the Duramax may not have those vibration issues (that would be my hope).

Jim Black (of RVS, FMC authorized repair facility - Morgan Hill, CA) and Leslie Hoagland of Motor Coach Restoration in Illinois have only dealt with older diesels: the 8.2L detroit and 6 cyl in line Cummins. Either of those engines will have vibration issues, but more importantly weight issues and a narrow torque curve that do in fact force structual strenghtening. That is why I eliminated them upfront. I know both Jim and Lesle,and respect them both but in this case they are both still thinking old school.

As Journeyman indicated, in the case of the FMC pounds are important and the difference between the Duramax and other modern light weight diesels eliminated all others on that factor alone.

Since my last posting, I was able to make contact with the current owner [he did not do the conversion] of the FMC that was converted a few of years ago and written up on The Diesel Page. He surfaced at an FMC rally held in Colorado last month. While I wasn't able to be at that rally, I have received some very complete descriptions of how the conversion altered the fuctioning of the coach. Those descriptions were all good!

Here are a few:
"The coach has a 5-speed model 1000 transmission. It turns about 1700 rpm at 65 mph." [note: In my opinion that is too slow.]
"When we started up La Veta pass, Jim Evans [440 carb powered] (in the lead) said over the radio that he wouldn't be insulted if anyone passed him, so I [440 fuel injection powered] pulled out and stormed up the hill past everyone [This included a turbo inline 6 cyl Cummins]. Dave Jacobs followed in the Duramax coach, and when I waved him to come on by, he passed us like we were nearly going backwards! It was very impressive - and sounded great, too."
"Coach #735 performed perfectly, getting 11.2 mpg pulling the Bimmer (left in Colo. Sprgs for A/C repair) and 13.8 mpg empty including going over 3 mountain passes over 10,000 feet including Wolf Creek Pass (10,550 ft) which is the curviest and steepest I've ever seen."
"Several miles out from Pagosa Springs, we started the long climb up Wolf Creek Pass (10,857 ft). I suggest that Dave proceed ahead, and they proceeded to disappear again ;-) I didn't push it [440 fuel injected]: we stayed near the 35 mph speed limit at 3500 rpm in 2nd gear (Allison AT545 4-speed) all the way up the climb."

It should be noted that no frame issues were evident with the Duramax converted coach even though it still had the stock frame.

As all of you can understand, having read the above plus additional comments any thoughts of an 8.1 vortec disappeared. It also encouraged me as to the thoughts of converting to a Duramax. I came to two conclusions: for this conversion, it needs to use the 6 speed double overdrive transmission so that the stock 4.62:1 differential can still be used as that combination gives a good transfer of torque to the ground with 65 mph at about 1900 rpm, and that if it would be possible to locate an LBZ it would be best. An LLY would also be fine. The above coach has an LB7.

I then made the mistake last week of typing in Duramax LBZ in the search window of eBay! To shorten the story, I am now the proud owner of a used LBZ that was obtained at an attractive price! I guess I am now commited.

The following is the body of an email I wrote to a fellow FMC owner:
"What this purchase did was commit me to a methodology in that I can no longer look for a matched engine/transmission set. It is now piecemeal and just do the stuff that has to be done to make the pieces work together. That will take awhile. One of the reasons I went ahead is that a matched Duramax LBZ and Allison MH (Motor Home) transmission doesn’t exist. No motor home manufacturer has used the Duramax to this date so they aren’t matched to a MH transmission. Motor home manufactures have either used a gas engine or Cummins or Powerstroke. I already had eliminated those engines so I had effectively eliminated a matched set with the MH transmission. That left the possibility of a matched LBZ with a 6 spd Allison, but one that would have to be converted from a standard arrangement to the MH version with the driveline parking brake. Given the attractive price I paid for this LBZ, I went ahead and set pattern.

"Now the game plan is to obtain a matched ECM (engine control module) and TCM (transmission control module) from a Duramax LBZ / 6 spd Allison equipped wreck including wiring harness(s) if possible. That will be used to control a used Allison 1000MH 6 speed. This will be a challenge to obtain as the 6 speed is 2006 or newer, but this is why the year or more timeline to complete the conversion. In my dreams, I would prefer to use the Allison 2500MH with the lower first and second gear, but the population of those is so small I can most likely forget it. Which ever model Allison (1000, 2200, 2500) I do end up using, I do want it to have a parking pawl. Not all of them have one. [Note: the 2550 has the pawl.]

"Then comes the question of how to control the transmission. One possibility would be to obtain the push button, paddle controller found in some newer motor homes. It is 100% electrical I believe. This could most likely be mounted on the inside of the drivers door (or left side of the drivers seat stand) and, therefore, not be involved with the dashboard or driver/passenger area. Whether or not it could be mounted into the dash in the area of the existing shifter is not known.

"So the “you” part of the “we” is to start looking for the pieces and parts needed to complete the job. Start crawling through the junkyards looking for donor vehicles for the above items.

"Understand that I am not committed to the actual conversion until all component parts have been secured. The Duramax LBZ that is now on the way can be resold if all other components are not located at a reasonable price or if some other issue prevents the conversion."

Who am I kidding!! :D I am now fully addicted to the conversion of my coach to a Duramax LBZ with an Allison 6 speed behind it and ALL issues will be surmounted.

You now have the current status and know what some of the additional parts
needed include. I am going to try very hard to get hold of a 2550MH transmisson. The lower gearing of the first two gears may over time prove to help alleviate any frame issues as the torque is then easily transfered to the wheels when starting out without needing a stiff frame to hold the engine back from rotating.

Wish me luck and if any of you come across any of the items I need (everythng!) please give me an email at Stephen at Heinrichs dot com.

I will post updates as major events happen.

[Dakster]

Nice... Glad you decided to try it. Good luck with locating all of the parts to do it. In the MH's I've driven all where 2003 and Newer, 40' with either cummins or cat motors and the allision tranny. They had the shifter you are talking about. It appears to be all electrical and I have seen them mounted on the arm rest, on the dash to the left AND right of the steering wheel. One had it in the center console area which was still reachable by the driver. They seem to be fairly flexible for mounting.

You may want to look in a MH junkyard to get the tranny and controller you need?

I look forward to updates!

[BigRabbitMan]

You may want to look in a MH junkyard to get the tranny and controller you need?
I look forward to updates!
One of the questions that I need to get answered is what trans controllers are compatible with the Duramax's ECM. Will a TCM that originally was used with a Cummins or International also work with a Duramax (GM) ECM or will GM's propietory programing also require a GM TCM to be compatable. Are the plugs compatable? I expect the transmissions to all be the same, just different controllers so I should be able to plug a GM TCM into any Allison transmission regarless of source.

Everyone's thoughts are welcome.

[BigRabbitMan]

Here is a link to where pictues of the engine I purchased are posted. The first couple of pictures are what I purchased and the last three are what greated me at the trucking terminal.
http://www.fmcowners.com/mbbs22/photos/photo-thumbnails.asp?albumid=29

I have just secured an engine stand and will now attach the engine to it where I can assess the shipping damage so that a claim can be submitted and so that the engiine will be properly stored and ready to be worked on when the time arrives.

[BillCarry]

I have a 6.5 TD 30 ' motorhome which I bought new in 1994 (one of the first 6.5 front engine units built by Georgie Boy and perhaps the industry). Loaded it weighs around 15,000 pounds.

I just passed 150,000 miles.

I have accurately calculated mileage on four or five trips from MIchigan to Florida and back and I consistently get between 11.5 and 12 mpg. I drive 60-62 mph on the interstates. With three previous, slightly smaller gas motorhomes (one GM 454 TBI and two Dodge 440 carb) I consistently got 7.5 to 8 mpg. My oil consumption has not changed since the engine was broken in and runs a quart about every 1800 miles. The over the road performance feels about the same as the gas jobs.

I'd say if you can pull this off with the Duramax you'll be real happy with what you get.

Bill Carry

[BigRabbitMan]

Bill,

Thank you for the input. As you did, with the 440 I am getting 7.5-8.0 mpg and would expect it to go to about 11-12 mpg. That lines up with your experience. I will get it done, but I do know that it will be a long involved project. That is why I went ahead and got a replacement 440 installed so that I can use the coach while I am gathering all of the parts.

What I am looking forward to is the expected improvement in general performace particularly in the mountains. That is where I expect to havest the benefits of the higher torque of the Duramax linked to the gearing of the 6 speed Allison through my 4:62-1 rear end.

Once installed it will be off to Mexico and Alaska!!

[journeyman]

Any updates?

Are you still converting?

[BigRabbitMan]

Yes, I am still converting, but the time line is probably fairly long. As it turns out , the shipping damage was minimal - tough engine! I am looking to continue the project by aquiring an Allison 6 spd in late spring and look towards making the install happen in mid to late summer.

Due to a pinched nerve in my upper back (since October) that is only getting better very slowly (typing still bothers it!) all physical activity is on hold. I am going to contact the mechanic son of my neighbor an see if we can take the engine down to his shop and, with it on the stand, identify what parts are missing, locate them and have him install them on the engine.

He drives a Duramax powered unit so he will be able to use it to help identify the missing accessories and bracktry etc..

I will have more time after the end of Febuary as that is when I semi-retire to about 25% time.

[BigRabbitMan]

Well, semi-retirement is just now happening, but am now supporting wife's schedule to assist daughter when granddaughter arrives in July. Then it will be preparing for spending most of September in the Philippines and then back to MY projects. I am looking for a forum that has the Allison transmissions as it's main subject as I need to start the searching in that area. I have solidly decided on using the Allison 6 speed as it will give me 1900 rpm at 65mph with no rear end modifications.

Does anyone have any suggestions on forum(s) for the Allison transmission?

Here is a mileage report by the present owner of the conversion to an LB7 of an FMC motor coach like mine that was previously covered by The Diesel Page. He will be making a 5000 mile trip in September and will do a more complete report at that time. He will record results at different speeds, etc.

"Pulling a 3500lb car at 70mph we got approximately 11.8mpg. Without the car behind, we got about 14.5mpg at varying speeds at mountain elevations.

The project creeeps forward!:)

[BigRabbitMan]

Here is the report of the mileage for a trip from S.D. to VT and back: "We averaged 61.2 MPH (according to "Miss Garmin") even with lots of road construction and slower speeds in the mountains and we averaged 13.8 MPG." This was a 3800 mile round trip. This is the coach that is the same as mine and was featured in an article in The Diesel Page several years ago and was discussed above. He normally tows a BMW.

That is the kind of results I would like when I eventually do my conversion with the LBZ that I have in the garage.

[BigRabbitMan]

Well I am back to having conversations about my project (the '06 LBZ is still in the garage!). I just talked with a used engine/transmission reseller here in the local area and he has a number of different model Allison's in stock. I have been looking at the 2550 as it has the lower gear ratios in 1st and 2nd and the parking pawl. Allison didn't allow parking pawls in new units if they were over 22,000 lbs. Mine is 14,000 plus an tow vehicle which could take me up to 18,000 lbs gross weight.

The question of the day is whether I should go with a 5 speed or a 6 speed. With my present rear end and wheels, which I will not change, the 5 speed would put the Duramax LBZ at about 2200 rpm at 65mph. The 6 speed would put the engine at about 1900 rpm.

To all of you Duramax folks that run with loads in that range a lot of the time, where should I target my RPM? Reasons?

[BigRabbitMan]

The question of the day is whether I should go with a 5 speed or a 6 speed. With my present rear end and wheels, which I will not change, the 5 speed would put the Duramax LBZ at about 2200 rpm at 65mph. The 6 speed would put the engine at about 1900 rpm.

To all of you Duramax folks that run with loads in that range a lot of the time, where should I target my RPM? Reasons?

Have changed the title to reflect the current question.

[BigRabbitMan]

Based on the discussion in this thread http://www.thedieselpageforums.com/tdpforum/showthread.php?t=34258, the decision has been made to use a 6 spd.

Now to find an Allison 2550 which is the model with the lower 1st and 2nd gear ratios.

[BigRabbitMan]

It is time to update this thread - the action begins!

Today I aquired a 2006 GMC Sierra 4x4 with an LBZ and 6 spd Allison (47,000 miles). So now the project goes into high gear utilizing the time and talents of two people: myself and a fellow FMC coach owner. The conversion will be done at his house as I have no room at my house. He is also very talented mechanically, electrically and with control systems.

I still have the LBZ in the garage, but we decided that it would be best to get a "roll over" donor vehicle so that we could utilize the maximum number of other systems instead of the minimum number of other systems. It is now our intention to integrate the compete GMC dash module into the FMC dash including physically. We will disable any unused functions, but will otherwise have a stock gauge/dash module in the FMC.

Right now the biggest unknown is the transmission issues I have discussed above.
1. Will a Duramax ECM function as well with a non-GM TCM as it does with a GM TCM?
... or,
2. Will a GM TCM work with changed gear ratios in the Transmission?

If you can give any help or direct me to a source of information on these two questions, I would greatly appreciate it.

Wish us luck as I pick up the donor vehicle in a day or so. The LBZ in the garage will be sold when we are sure we don't need anything from it as well as all excess parts of the roll over donor GMC Sierra 4x4.

Stay tuned,

[BigRabbitMan]

Right now the biggest unknown is the transmission issues I have discussed above.
1. Will a Duramax ECM function as well with a non-GM TCM as it does with a GM TCM?

If you can give any help or direct me to a source of information on these two questions, I would greatly appreciate it.

Question #2 was answered elsewhere and the answere was NO.

That leaves Question #1. The reason for this question is that I am considering going with an Allison 2550 due to my driveline parking brake requirement. I would like to have it with the wide grear ratio if I can get it flashed as a 6 spd by Allison. If that can be done, then the question above is very pertinate as it is pointless if the LBZ will only function properly with a GM TCM.

My thoughts are that the LBZ functions with a manual transmission, it should be fine, but I can't find out what inputs other than output shaft speed, if any, are needed by the ECM.

Thaniks,

Thanks,

[BigRabbitMan]

That leaves Question #1. The reason for this question is that I am considering going with an Allison 2550 due to my driveline parking brake requirement. I would like to have it with the wide grear ratio if I can get it flashed as a 6 spd by Allison. If that can be done, then the question above is very pertinate as it is pointless if the LBZ will only function properly with a GM TCM.
After many discussions and consideration of verious factors, the decision has been made to use the Allison from the donor vehicle and its control module. I will not have the wider ratios for the first couple of gears, but I can live with that.

I have confirmed with the Allison technical advisor of Allison West that the GM 1000 can be converted from 4 wheel drive to 2 wheel drive with provisions for the standard driveline brake which is a requirement in my case. He will be researching the part numbers to pass along. The transfer case will be removed and the correct tail housing and tail shaft will be installed. He may also have a buyer for my transfer case!

Pictures of the donor vehicle (2006 Sierra 2500) are here: http://travel.webshots.com/album/579528614eUJYCC

As we move throught this project pictures will be added to that album.

A vacuum pump from a 2002 Lb7 has been secured to provide the vacuum needed for the brakes. I am still in need of a second alternator with bracket and an idler so that I will have a dual alternator setup.

Repair manuals have been purchased and have arrived so that wiring needs can be studied and the best procedure for removeing the harnesses from the donor can be developed.

... to be continued ...

[BigRabbitMan]

An update is in order. Work on the donor GMC Sierra has continued. Since we are working outside, we are subject to weather on Saturdays as well as family matters. The combined effects greatly reduced our work days these last two months.

We have desmantled the front end while tagging anything that we will be hooking back up in motor after the transplant. we are almost ready to extract the LBZ and Allison from the donor. It will then have the output shaft and housing changed from a 4x4 set up to 2 wd with a driveline parking brake.

I have posted a number of pictures at the link in the above post. Go take a look. As we progress I will continue to add pictures.

[BigRabbitMan]

We are doing a "full swap" to the extent possible in this case. You could do a "minimal swap" which would not involve the dash cluster, etc. and with that swap you would retain the original guages/dash. We are doing it as the full swap so that the benefits of the full guage cluster and the Driver Infornation Center (DIC) would be retained. This includes cruise control. The exisiting systems on all non-computer controlled engines will not work as there is no linkage for the cruise control to attach to.

An example of the two levels of conversion are like what we are involved in right now when it comes to the engine fan. The donor fan will not work as it is a puller and not a pusher fan. It also has an ambient air (exiting the radiator) thermal viscous clutch to control fan speed which also will not work as the air is going the opposite direction and will never engage the fan.

The simple solution would be to just remove the clutch and bolt the fan, by using an adapter, to the idler and have the fan operate at engine rpm the same as our fans do on the 440, 8.2, 5.9 etc. The drawback to that simple solution is that the fan is always drawing full horsepower for the given rpm and, therefore, energy and fuel.

In an attempt to improve on that situation and have the fan only operate at the speed needed for conditions, we are currently looking for a fan clutch/controller combination that will electrically control the fan speed via a viscous coupling based on engine coolant temperature. When cruising on flat land in cold weather the fan could operate at significanlty less speed than what is needed on a hot summer day if we find the right combination. Given the amount of air that the fan will be capable of moving, the difference can be significant over a number of miles.

Stay in touch as we work our way through this project. Your questions/sugggestions are always welcome.

[BigRabbitMan]

We we haven't made much progress lately as we are working outside and it has been raining every weekend here in Northern California. The mountains have 165% of normal snow load! That has given us time to debate another conversion issue/question.

The question is: Should we move the donor steering wheel and upper steering column as well as the dash instruments to the FMC from the GMC Sierra?

Changing the column would add the complications of doing that transfer, but would simplify the wiring as the four radio control switches, two DIC switches, shifting switch, tow/haul switch and cruise control switchs would no longer be needed to be rewired or moved to dashboad switches. The steering wheels themselves are within 1/4 inch diameter of each other. It would also be nice to have all of those controls on the "smart" steering wheel with the factory lighted rocker switches and their symbols.

We were fortunate to have another FMC owner who is an aircraft mechanic stop by on his way south so that we could visit and debate the steering column question. After that discussion, I believe we will be adding that change to the list of changes.

My coach will move to Eric's next weekend. In the following weeks the engine and transmission will come out of both the donor unit and the FMC. At that point, more pictures will be posted and we may have some more issues to solve.

To be continued .........

[BigRabbitMan]

After much delay and sidetracks to do other projects, the conversion project is continuing. All of the rear end stuff has been removed (bumper, exhaust system, radiator, panelling etc. Now removeing some of the engine asessories for easier extraction and disconnecting the things that connect to the engine. Also all of the firewall stuff will be removed as well. A few new photos have been posted in the album linked above.

Due to time constaints, we will not be moving the steering wheel over to the coach. That may happen later. First, we will get the coach back on the road.

[DieselDavy]

Great story! Keep us updated!

[BigRabbitMan]

Great story! Keep us updated!

The 440 is now out! Yeah!!
http://travel.webshots.com/album/579528614eUJYCC?start=48

That link will take you to the current pictures with commentary. A long tedious process of preparing the coach for the Durmax will now begin.

[BigRabbitMan]

Continuing to progress! Go to pages 6 and 7 of the above linked photo album. It shows what we have to clean up and, finally, the clean firewall. A few more things to do and then the sound suppression material can be applied to the existing firewall and then a new sheet of aluminum to form a new firewall. This will result in a double walled firewall with sound suppression material between the two layers of the firewall.

[BigRabbitMan]

The TURNING POINT has been achieved! The installation of the first of the new things has started. While more things (throttle cable, wires, center section of dash, etc.) still have to be removed, the lining of the engine compartment has started. It is rewarding to be putting something into the coach instead of taking something out. I have started the installation of the FatMat sound suppression material which will be followed by 1/4" small cell foam board and by 1/8" sheet aluminum. It can be seen at the above link. :D:):D

[BigRabbitMan]

Progress continues. Here I am putting in some of the last of the approximately 75 rivets that hold the new engine compartment liner in place.

http://travel.webshots.com/photo/2336301740012124553xZcVIQ

The next photo shows the finished firewall before anything has been attached to it. Attaching things will be the next phase after we finally remove the new engine from the donar vehicle this next weekend. We have left the engine just sitting in the donar vehicle to this point as it was secure there and we did not need it to be out to this point in time. It will still be awhile before it gets put into the FMC as there is still a lot of prep work to do to the FMC and I need to take the transmission in to have the tail shaft and housing changed to convert the transmission from 4-wheel drive to 2-wheel drive and to provide for attaching the driveline parking brake.

If anyone wants to convert from 2-wheel drive to 4-wheel drive, I have most of the components!

[BigRabbitMan]

Again, progress continues. I have just posted 26 more pictures of the progress of the project. They cover the removal of the engine from the donor vehicle and the changes to the transmission and the first pictures of the dash area of the motor coach and what will be happening there. This link will take you to the first of the new pictures.
http://travel.webshots.com/photo/2917414770012124553yllrEt
The next big thing will be the temporary positioning of the engine so that motor and transmission mount brackets can be designed and built.

To be continued!

[BigRabbitMan]

I have just learned that the site where I have the pictures posted (Webshots) is reinventing itself and so the current links to pictures will probably stop functioning some time in November. After they have done their reconfiguration I will go back and attemt to replace the links with new ones that will work.

Sorry for the complication.

[BigRabbitMan]

I have just learned that the site where I have the pictures posted (Webshots) is reinventing itself and so the current links to pictures will probably stop functioning some time in November. After they have done their reconfiguration I will go back and attemt to replace the links with new ones that will work.

Sorry for the complication.

Ok, I need to bring everyone up to date. The FMC Owners Club site now allows nonregistered visitors to view the photo albums and the postings in the forums. This allows me to link you to that album so that you can continue to follow my project.

A lot has been done and there are about 5 more pages of photos with commentary since my last posting on this site. The entire project did get slowed with nothing happening for several months this spring and summer due to my moving from Dixon, CA to Cottage Grove, OR. The coach remains in Gilroy, CA so, once my OR move is complete, I will be living part time in the coach until it is done.

Here is the link where the last dead link above left off.

http://www.fmcowners.com/mbbs22/photos/show-album.asp?albumid=77&photoid=2068

Your comments and suggestion are always welcome.:)

[More Power]

Thanks for keeping us up to date. Looks like quite a project! Jim

[BigRabbitMan]

I am back to working on this conversion project as my move to Oregon is complete. I am now splitting my time between being in Oregon and working on the coach in Gilroy, CA. In addition to doing some interior upgrades, I have progressed with the conversion project. You can select my handle on the FMC website to see other albums that detail other things I have been doing in parallel with the drive train conversion.

Here is a link to the last items I have worked on. You can go back to earlier pages if you have not been following this project.
http://tinyurl.com/jw6u55j

Take care,

[GordonMarks]

Cool Stephen!
I remember doing all of that tagging, fitting, refitting, figuring(figgerin down here) & refiguring over & over. I think that I could just about flip to the service manual page I needed in either the 99 or the 2001 book. Used about 15 pads of yellow stickies in the process. It takes A LOT of digging AND weeding out the Lawyer BS that makes up most of the manuals.

Stick with it & keep posting!
Gordon

[BigRabbitMan]

Work continues! Here is a link to the most recent page of pictures of the project. This is page 15.

http://www.fmcowners.com/mbbs22/photos/photo-thumbnails.asp?albumid=77&Page=15&sortdir=asc

[BigRabbitMan]

Some more steps completed. There is just so many step to complete!!

Here is a link to a photo of the engine essentially "in position". This is a test fitting to ensure everything fits and to position the engine so that the motor/transmission mounting brackets can be designed and located.
http://www.fmcowners.com/mbbs22/photos/show-album.asp?albumid=77&photoid=2871

The engine will then be removed and the mounting brackets welded into place, final things done to the engine and then the engine will go back in permanetly. The rear frame cross member will also need to revised.

To see how the dash cluster was installed go to the previous page of pictures.

While work continues, I will be gone for the next couple of weeks.

[esbstuff]

Can you post (or repost) the part numbers to the driveline brake conversion? Was it hard? Thanks!

[BigRabbitMan]

Can you post (or repost) the part numbers to the driveline brake conversion? Was it hard? Thanks!
Actually, I don't have the part numbers. The Allison 540 4sp tranny that I am replacing already had the brake on it and so I just had the Allison distributor move it over to the Allison 1000 when it was being converted from having a transfer case for 4 wheel drive to being a two wheel drive setup. The tail shaft housing must have the provision for the brake. Allison can give you the number for that tailshaft housing.

As a side note, the website that hosts my photos is having some problems as a result of foreign spammers and is no longer available without registering and no longer has the pictures from Dec 2013 to now. When that gets sorted out I will update the pictures and provide a fresh link.

Progress does continue as I am in the process of positioning the engine and tranny so that the motor mount brackets can be welded into place.

[BigRabbitMan]

When that gets sorted out I will update the pictures and provide a fresh link.

Progress does continue as I am in the process of positioning the engine and tranny so that the motor mount brackets can be welded into place.

The engine is now in place and the hosting website for the pictures is back up so that the links will now work again.

Here is the link to where the mounts are being put into place. One had to be done twice!
http://www.fmcowners.com/mbbs22/photos/show-album.asp?albumid=77&photoid=2882

The last picture as of today shows the engine with the serpentine belt installed with the dual 145 amp alternators. The belt will come back off temporarily while I double check torque on all of the bolts then it will go back on permanently.

Next up is designing the intercooler, radiator and tranny cooler mounts and plumbing. I will be using a water-to-air intercooler instead of an air-to-air intercooler due to the limited stack space and the fact that I do not have ram air and have to use a pusher fan.

[More Power]

Looks like it's coming together for you. Thanks for the update. Jim

[BigRabbitMan]

Looks like it's coming together for you. Thanks for the update. Jim

Yes, it is getting close. Here is a link to page 25 http://www.fmcowners.com/mbbs22/photos/photo-thumbnails.asp?albumid=77&Page=25&sortdir=asc of the 28 pages of pictures. Depending on where you left off in your picture viewing you may need to page back to follow the project and not miss a section. All fluids except engine coolant are in place.

The radiator will be installed tomorrow as the shroud was completed today. We will be pulling the front to back wires this Saturday so it is getting close to the time that we will be turning the key!:):)

[BigRabbitMan]

Yes, it finally fully came together!

The first test miles have been logged!

All I can say is SWEET!, SWEET!, SWEET!!!!! It has good acceleration, shifts as smooth as butter and is very quiet inside. I don't have a video from inside as of yet so I cannot give you a sound level test, BUT, I can give you an 8:43 min video from the chase car of a portion of the initial test drive. The chase driver (Eric) and I were on speaker phone to each other so if you listen carefully you can hear my side of the conversation.

When it starts we are comparing speedometer readings and it appears that mine is reading about 3 mph faster than actual (his). That will be compared to a GPS at some point in the future. I am turning about 1850-1900 rpm at 65 mph. At about 1:11 min remaining I advise Eric that I am going to see if it makes black smoke. I floored it and it just blew gray and dust off the road. That does show that the engine is running efficiently. My acceleration rate was very good for a motor home!

Here is the link to the video, enjoy: https://vimeo.com/142810917

The Vimeo site also has a startup video and another one. The photo album linked above is now up to 31 pages so go there for the detail of what was done.

Today we took it for a run over a 1300 ft pass and back that has 6% sections of grade going both ways. It performed very well. Going up the five or so mile grade I needed to keep the revs up as a pusher fan is not as efficient as a puller fan with ram air. Other than that all is good.

The day after tomorrow I will be headed home to Oregon with the coach pulling my '87 Subaru Brat tow vehicle. Look for me around the Northwest primarily but I will be in Carthage, MO next June.

[a5150nut]

Good to see you got her on the road.

[BigRabbitMan]

Good to see you got her on the road.

Yes, it feels and runs really well. I have subsequently checked the speedometer vs my GPS and they agree so my tranny to ground gearing matches what GM expected. That makes most of the driver info center readings reasonable within GM's error factor (which can be large?). It does significantly aid in speed monitoring. This thing keeps wanting to float up to 70 or so which is getting a little fast for a motor home.

For the first 222.2 miles, the DIC reports 12.9 mpg. That compares to 7.0+/- for the 440 that was removed.

[a5150nut]

You are in my old stopping grounds. I used to work for Operating Engineers Local 3 there in Morgan Hill. Used to lived off Monterey at Capitol in SJ. Recognized the roads on your test drive. Have you tried over Pacheco Pass yet?

That's not one of the FMG rigs that used to be at the repair shop on Monterey just north of Morgan Hill is it?

[BigRabbitMan]

You are in my old stopping grounds. I used to work for Operating Engineers Local 3 there in Morgan Hill. Used to lived off Monterey at Capitol in SJ. Recognized the roads on your test drive. Have you tried over Pacheco Pass yet?

That's not one of the FMG rigs that used to be at the repair shop on Monterey just north of Morgan Hill is it?

That's quite a coincidence! Yes, my rig has been at the shop (RVS) on Monterey Blvd from time to time. By the way, that shop closed down a couple of years ago. And Yes, I have been over Pacheco Pass (1300 ft) three times now. Pulls it very nicely. We went over and back on our second test run and then I went that way to show coach to others in Modesto, Ripon and Sacramento. Came back via the Altamont pass and the Sunol grade. Maintained my 60 mph all the up the Sunol grade (steep but short).

With all of that turning out well, I then had the confidence to hook up my Subaru Brat tow car and head to Oregon via my old home town of Dixon, CA (needed to stop at Pedrick Produce!). The trip north up I-5 was 583 miles and I got 13.1 mpg as measured by the DIC and verified by my carefully filling the tank once I got home to Oregon. So the real test was the Siskiyou Pass just north of the CA/OR border. It is 7 miles of 6% grade going up and 7 miles of 6% grade going down the other side with the pass at about 4,300 ft.! That followed two other passes at over and under 3,000 ft.

The run home proved two things: The first is that I now have a very responsive coach that is fun and rewarding to drive, and the second is that with the power available, I can generate heat faster than I can get rid of the heat. I knew that was a possibility when I compared the new pusher fan (and the fact that it is a pusher configuration) I installed to the one that came out of the 2006 GMC Sierra. While the coach is very drivable at present, at some point I will need to increase the heat rejection rate and that will start with a new fan with more blades, etc.. The coach has the power to climb a 6% grade at 60 mph, but needs mods to do it on long grades to control the heat issue. Coming home I just did what truckers do on grades and that is to just gear down, go slower and keep my revs up. That reduces the work on the engine which reduces heat generation and the high revs blows more air through the radiator which gets rid of more heat.

Sorry for the delay in responding, but it was because I was on the road north and doing things once I got home.

[a5150nut]

They closed that shop just before I retired end of November 2013. Left San Jose June 28 2014 just before 183 days into the year so we wouldn't owe taxes for the entire year. Registered in Nevada dr. license, vehicles, and to vote to be sure CA couldn't claim us. Stayed in Nevada a couple months then wandered across to Tennessee and bought a house. After years in a 36ft fifth wheel it sure feels good. And a lot better prices here than CA. Oh and we have water here too.

When I bought my fiver it was in Los Banos. Picked it up at the Automate factory after they tuned it up for us. I had a 94 K2500 with 5 speed then. It was a chore but pulled Pacheco in 3rd gear. Paced with two semis, got passed by two, and passed two going up the hill.

What a difference it is with my K3500 Duramax and Allison though. Duramax is much more of a work horse. Still have to watch boost and pyro gages and ease up when the temps go up. On the open interstate I can usually find a semi running about my pace and fall in behind and draft a little. Just watch boost gage drop and you know when you have caught the sweet spot.

From Nevada we stopped in southern Utah to visit Zion and North Rim. Then down to Flagstaff. There are some long steep grades that way. Longer than 395 out of Bishop. But again, watch the gages and remember I'm retired and don't have to be in a hurry.

Back to your rig. Can you add an auxiliary radiator and fan any where under it? Or an extra oil cooler some where? I'm sure its still a work in progress so time will heal every thing.

Good luck with it and keep us posted.

[BigRabbitMan]

Can you add an auxiliary radiator and fan any where under it? Or an extra oil cooler some where? I'm sure its still a work in progress so time will heal every thing.

Good luck with it and keep us posted.

The first change will be a different fan. Once I see what that does, then we will go from there.

[FamilyTimeRV]

Thanks for all your efforts and information. We're looking to add an affordable way to rv with 4 children. The FMC (possibly GMC) is our choice with an efficient power plant. We may follow your example.

How's your conversion working out -- no updates in the last few months.

Also, are there any 20-20 hindsights that would benefit a similar conversion?

Kevin H
still in planning & prep stages

[BigRabbitMan]

Thanks for all your efforts and information. We're looking to add an affordable way to rv with 4 children. The FMC (possibly GMC) is our choice with an efficient power plant. We may follow your example.

How's your conversion working out -- no updates in the last few months.

Also, are there any 20-20 hindsights that would benefit a similar conversion?

Kevin H
still in planning & prep stages

Hi Kevin, sorry for the delay in responding. Had things happening that kept me away. I am glad to assist you in your information gathering. The first thing to understand if you are looking at any older motor home, you need to be at a minimum a mechanic to some level as there will be things that need attention/repair/upgrading and it would be cost prohibitive to have that stuff done by a regular shop in most cases. Since you are on this site, I expect that you are covered in that respect.

As to things that I would have done differently, the only one of significance is that I need a larger fan. Another person is in the process of doing the same conversion to his FMC that I did and has secured a better fan. I expect that at some point I will be getting that same fan, but in the meantime I just have drive conservatively going up grades. You can visit both my complete photo album and his (still in progress) on the FMC Owners Club website. The link is: [URL="http://www.fmcowners.com"] . His coach number is 1027 and mine is 1046. He is up to 227 photos in his album and I have 371 in my album. There is also a discussion of both projects in the forum area in the Mechanics section. Feel free to register on that site so that you can post questions in the forum area. He is doing somethings differently than I did but no two people do something like this the same. Not better or worse, just different. He will be doing some suspension things as well as the engine change in his case.

Two major things that I like about the FMC is the low profile and the quietness with the engine in the rear. The GMC also has the low profile, but you do have the engine up front on that one with the attendant engine noise. If you want to convert one to diesel, I think it would be much more of a challenge with a GMC. I am not aware of a compatible engine/tranny for the GMC. There may be one, but I am not aware of one. When you say "efficient engine", I don't know how you define efficiency but if it is more than 8 or so mpg, diesel is the only way you will get there.

There are FMC's that have already been converted to diesel that come up for sale from time to time, but you need to ensure that the conversion process was done properly. That is particularly true of the heavier diesels like the Detroit 8.2 or the Cummins 5.9. Length with the Cummins also causes some issues that have to be addressed.

Traveling with four children raises some questions in my mind. The first is the ages of the children as that will be a factor in how much "space" each one needs. The "A" or dinette model with the optional bunk beds is set up to be able to sleep six people. As they get larger, some have had the teenage children sleep in a tent adjacent to the coach when camping for more than one night.

I haven't had any updates to my thread here as I haven't done anything additional to the coach. In Feb I did travel about 800 miles south to Buellton, CA for a coach rally and back - just had to take it easy going up six percent grades! On the way back I did get 13.6 mpg measured which is very good for a motor home. It is sweet to drive and very quiet with the rear engine and the sound proofing that I did to the firewall. I can hear that it is running, but that is about all.

I am in Oregon, in what state are you located?

[JeepSJ]

Very nice! Are you monitoring your intake air temps? I was wondering how that water/air intercooler was working.

[convert2diesel]

Thanks for all your efforts and information. We're looking to add an affordable way to rv with 4 children. The FMC (possibly GMC) is our choice with an efficient power plant. We may follow your example.

Kevin H
still in planning & prep stages

Kevin:

Just a few thoughts. I am going through the same thought process as you are. Mind you, I don't have to factor in 4 kids.

Currently I am leaning towards the GMC. The original design was not only brilliant but it has survived the test of time with a large and active owners community. Having said that, for your purposes, shoehorning yourself, significant other and four kids into a GMC would be tough with any of the available floorplans.

Additionally, the front drive system comes out of the Olds Toronado/Cadillac Eldorado of the same vintage. Without major surgery, that means you are stuck with the THM 425 transmission (basically a 400 with the torque convertor and front pump attached to the engine with a chaindrive to the rest of the tranny turned around and going forward. Still a great transmission, especially if you can find a "switch pitch" trans from a 67 or 68 car. Essentially gives you a 6 speed tranny.

The bell housing is a "BOP" bolt pattern so if you use any other engine you would have to get an adapter plate, modify the engine oil pan to accommodate the right hand drive axle and fabricate a front mounted engine mount. There are a number of 6.5 turbo conversions out there as well as a couple of Duramax conversions.

If you are still interested in the GMC, I would suggest you look into the GMC Co-op in Orlando Florida. Jim Bounds is the by far the most knowledgeable person in the community.

http://www.firefightmarine.com/gmccoop/

This thread has me looking at the FMC as an alternative. Love the concept of the independent rear suspension and pusher engine layout. This plus the added room for the family would make sense for your uses and open up your options for engine trans combinations. Unfortunately they are not only the same vintage as the GMC but there were far fewer manufactured. I would question the availability of parts, specific to this platform.

I have also started looking at the Airstream Motorhomes. Lots of them out there with a 40 year production run including some pusher versions later on. Even today, they are still manufacturing a motorhome based on the Mercedes Sprinter platform. Still trying to get some information on the various versions and separating the good from the bad.

From a cost point of view, I would seriously analyse how you are going to use this motorhome and specifically, how much you are going to use it. Upgrading any of the powerplants in these vehicles to a newer engine is far easier and cheaper with a gas conversion than the diesel. In other words, you are going to have to pack on lots of miles to justify a diesel conversion from a cost point of view.

The new "LS" series GM gas engines are plentiful, with an extensive aftermarket support system in place. Properly configured, they can be programmed for very acceptable fuel consumption and with reasonably inexpensive "go fast" parts can lay down some very respectable power. Based upon my research into the GMC, I could do an LS conversion for about $5,000 less than any decent diesel conversion, plus, it can be fixed on the road by any reasonably equipped garage. Even Bubba in lower Buttkiss is probably conversant with this engine family.

Myself, I am leaning towards a GMC with either an AMG 6.5 or LS engine and a switch pitch transmission, upgraded suspension and brakes and a total re-working of the body. I expect the cost to be in the 30 grand area, including the initial purchase. Not much more than a reasonable tow behind trailer.

Hope this helps.

Bill

[BigRabbitMan]

Very nice! Are you monitoring your intake air temps? I was wondering how that water/air intercooler was working.

That question raises one of the little glitches with my system. I installed the Banks system with their IQ monitor/controller with lots of readouts. The problem I have is that it doesn't work with the long extension cord that I have to use to reach the front (30') so that I can monitor things while on the road. It works fine while only using the short cord that comes with the unit but since my engine is in the rear, I can't use it while driving. I will be contacting Banks to see how this can be resolved. In the meantime, I know the water is warm/hot when stopping so it is taking heat out of the air stream but I don't know the actual air temp while under load.

I do have a second issue as the turbo vane position sensor is not functioning with the new sensor. The result is that I am always at full boost so have driven very conservatively. I will be starting a new thread about that issue at some point.

[BigRabbitMan]

I expect the cost to be in the 30 grand area, including the initial purchase. Not much more than a reasonable tow behind trailer. Hope this helps.

Bill

Bill has done an excellent evaluation. His cost estimate is very good for a conversion done properly. In my case, I spent more than needed in some areas and already owned the coach and I ended up with a total cost of about $27,000 for the Duramax conversion. The other person that is currently converting an FMC to a Duramax expects his cost to be the $30,000 number including the purchase price of his coach. I expect that number will be very close to what his actual turns out to be.

In the case of the FMC, a conversion/upgrade to modern gas engine/tranny setup would be much cheaper and that is what I would recommend for most people as most motor homes will not get the mileage on them to begin to justify the cost of the diesel conversion. With the FMC, a gas conversion is fairly straightforward with few complications. Mainly engine/tranny mounts and gauges. But again, it takes many miles to justify a conversion verses, in the FMC case, just doing a rework of the existing 440 with possibly upgrading to a fuel injection system. With the 440, I pulled 6% grades at 45 mph passing many other motor homes!

As to parts availability, with both the FMC and GMC there are support groups out there and sources of parts have been identified for most things. As an example, I have just ordered all of the steering linkage parts for my coach as with 160,000 miles it is time for work on that end. They are all off the self items still today as they were/are used on many other vehicles.

Rollin', rollin', rollin',

Stephen H. , FMC #1046

[convert2diesel]

That question raises one of the little glitches with my system. I installed the Banks system with their IQ monitor/controller with lots of readouts. The problem I have is that it doesn't work with the long extension cord that I have to use to reach the front (30') so that I can monitor things while on the road. It works fine while only using the short cord that comes with the unit but since my engine is in the rear, I can't use it while driving. I will be contacting Banks to see how this can be resolved. In the meantime, I know the water is warm/hot when stopping so it is taking heat out of the air stream but I don't know the actual air temp while under load.

I do have a second issue as the turbo vane position sensor is not functioning with the new sensor. The result is that I am always at full boost so have driven very conservatively. I will be starting a new thread about that issue at some point.

Stephen:

I concur with your decision to contact Banks. Your sensors are either resistance or hall effect, both would be adversely effected by length of harness. Same goes for the EGT. There might be a way to calibrate the unit to compensate for the length of wire but only Banks could tell you how. I do know that EGT leads can be purchased with different length/resistance specs.

Good luck

Bill

[Hal StClair]

Not to hyjack a thread but I have a 1977 GMC that I've installed a 2000 H1 6.5TD with 4l80e trans. I used a B/W transfer case from a Revcon MH and went forward to a 2012 9.25" AAM front diff out of a one ton Chevy. We've put about 3000 miles on it since September and have very few nit's to pick so far.
Not a swap for the faint of heart for sure, but a nice match.
Hal

[BigRabbitMan]

The following is a report that I just posted on the FMC Owners Club website. It should bring you up to date as it includes a mileage check on flat ground and one in the mountains.

**********
Since I now have just under 5,000 miles on my conversion, I thought that I would do an update.

The first thing to note is that I am very happy with what I call the "drivability" of the coach. I like the ease of merging with traffic at speed, not slowing down for most hills, engine starting in a revolution or two, butter smooth shifting, a 700 mile fueling range, an even quieter interior and other smaller factors. Many people are interested in what my fuel mileage is as that is a significant factor with any motor home. Historically, with the 440 I got about 7.0 mpg most of the time. That is probably about average for an FMC.

As expected, I have seen a significant increase. Since fuel mileage varies with driving style, weather, terrain etc. I decided to do some close measurements under specific conditions to help define what was occurring rather than just post a series of numbers. So on a recent trip to CA I decided to do a flat land test and a mountain test.

The flat land test was from Redding, CA to Bakersfield then back north to Santa Nella, CA. That was a run of 674 miles over three days time. The first half of the trip was with a storm coming in and a lot of cross wind. The second half was with relatively calm winds. I also made five diversionary trips into towns for various reasons so it was not all straight down the freeway driving. I spent most of the time in the truck lane at 60-63 mph as it was a comfortable driving speed and I didn't want to be in and out of the 70+ mph left lane. The net result was that I got 14.7 mpg for that segment of the trip. I was not towing the Subaru Brat.

For the mountain segment, I went from Redding, CA home to Cottage Grove, OR. The beginning and end of the trip were at a similar altitude with an initial gradual climb from Redding to Weed at 3,900 ft. It then dropped down to the Shasta river and back up to 3,000 ft then back down to the Klamath river. Those were 4 or 5 mile 5 & 6% grades after some flat stretches. It then went from the Klamath river down in the canyon up to the top of the Siskiyou pass in Oregon at a little over 4,100 ft which is the highest point on I-5. After dropping down the 7 mile 6% grade into Ashland it became a series of ridge crossing with the first several at the 2,000 ft level then into the valleys in between. As I continued north, the ups and downs became less significant until I reached home in Cottage Grove. Again, I was primarily in the truck lane except when passing trucks on grades. When descending 6% grades, I slipped the Allison 6 speed tranny into third gear (which is the same gearing as second gear in the 727 tranny) and came down the grades at 50-55 mph without needing to use the brakes.

The mountain portion of the trip was 301 miles and the coach got 13.3 mpg which is a respectable number for mountain driving in my opinion.

With those two numbers in mind and the conditions that created them, I expect my long term number to be somewhere in between them. Towing the Brat will probably reduce those numbers by a mile per gallon. Even with this kind of fuel mileage, it will take a lot of miles to recover most of the cost of the conversion excluding the unpaid labor cost for myself and the others who invested significant hours as well.

But, yes, I am glad that I did it and hope to see all of you on the road or at a future rally. Schedule yourself for the June Mega Rally in Carthage, MO and you may have the opportunity to take my coach for a test drive.

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There is now a second FMC owner converting his coach to a Duramax with 6 speed Allison. Here is the link to his thread on the FMC Owners Club website. He, also, has received good information from this site and its members. http://fmcowners.com/mbbs22/forums/thread-view.asp?tid=683&posts=54&start=1

[BigRabbitMan]

In the above post I mentioned that I was going to a rally in Carthage, MO from my home in Oregon. Well, I went to that rally and then continued on to the East coast including SC and Virginia, on up into Canada through Detroit, then back via MN and South Dakota. In all, from my door back to my door was 8,424.6 miles! It was a great trip and it gave me a chance to drive the coach extensively under different conditions and see how it performed.

It met all of my expectations and much more. At my Canada stop, we tweaked the adjustment of the front end elements and got the last of the play out of the system. It now tracks like it is on rails.

Up until the Canadian stop, I ran the Banks tuner on Normal or the stock tune. At that point I changed it to the Economy tune just to see what, if any, difference it would make. Up until that point, I had 11,289 miles on the conversion with an average of 14.02 mpg. From that point home via the northern route with a couple of diversions along the way, the coach averaged 15.08 mpg over that 2,907 miles.

Yes, I am very surprised and pleased to be getting mileage like that in a 15,000 lb. motor home. I will continue to monitor fuel mileage for the next year or so just for the record.

I thank the group for its support of this project,

[a5150nut]

Glad to hear of your success. That's a long ways from Morgan Hill where it all started.

[BigRabbitMan]

Time for an update. The coach was running a little warm when climbing hills so I converted the fan to a larger unit and changed the radiator back to the original FMC stock radiator which is a five row brass unit. I can now take 6% grades at 60 mph and not have the temp gauge move at all.

I have also gotten a lot more miles on it as I have now put 48,000 on the conversion in the three years since it was completed. My measured fuel mileage over that distance has settled in at 13.43 mpg. That includes all fuel after the initial fill up.

Driving my coach with the D-Max LBZ and 6sp Allison is a sweet experience.

I am a happy traveler!

[DieselDavy]

Those are some pretty good numbers for as much as that thing weighs!
Enjoy!

[arveetek]

In the above post I mentioned that I was going to a rally in Carthage, MO from my home in Oregon. Well, I went to that rally and then continued on to the East coast including SC and Virginia, on up into Canada through Detroit, then back via MN and South Dakota. In all, from my door back to my door was 8,424.6 miles!


If you should ever find yourself coming through Carthage, MO, again, please let me know. I work for an RV dealer here in Carthage, and would love to see your rig.

Casey