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Thread: Converting early gas MH to Duramax? Possible?

  1. #21
    Join Date
    Mar 2000
    Location
    Sylvan Lake, Michigan, USA
    Posts
    52

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    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

  2. #22
    Join Date
    May 2007
    Location
    Dixon, CA
    Posts
    84

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    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!!
    Stephen H.
    BigRabbitMan
    1976 FMC Motor Coach #1046
    Formerly 440, now LBZ
    Rear engined w/4 wheel independent suspension.
    Tow car: 1987 Subaru Brat 4x4
    http://www.fmcowners.com/mbbs22/phot...asp?albumid=77

  3. #23
    Join Date
    Jan 2005
    Location
    Kazan
    Posts
    27

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    Any updates?

    Are you still converting?

  4. #24
    Join Date
    May 2007
    Location
    Dixon, CA
    Posts
    84

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    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.
    Stephen H.
    BigRabbitMan
    1976 FMC Motor Coach #1046
    Formerly 440, now LBZ
    Rear engined w/4 wheel independent suspension.
    Tow car: 1987 Subaru Brat 4x4
    http://www.fmcowners.com/mbbs22/phot...asp?albumid=77

  5. #25
    Join Date
    May 2007
    Location
    Dixon, CA
    Posts
    84

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    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!
    Stephen H.
    BigRabbitMan
    1976 FMC Motor Coach #1046
    Formerly 440, now LBZ
    Rear engined w/4 wheel independent suspension.
    Tow car: 1987 Subaru Brat 4x4
    http://www.fmcowners.com/mbbs22/phot...asp?albumid=77

  6. #26
    Join Date
    May 2007
    Location
    Dixon, CA
    Posts
    84

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    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.
    Stephen H.
    BigRabbitMan
    1976 FMC Motor Coach #1046
    Formerly 440, now LBZ
    Rear engined w/4 wheel independent suspension.
    Tow car: 1987 Subaru Brat 4x4
    http://www.fmcowners.com/mbbs22/phot...asp?albumid=77

  7. #27
    Join Date
    May 2007
    Location
    Dixon, CA
    Posts
    84

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    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?
    Last edited by BigRabbitMan; 03-31-2009 at 20:14.
    Stephen H.
    BigRabbitMan
    1976 FMC Motor Coach #1046
    Formerly 440, now LBZ
    Rear engined w/4 wheel independent suspension.
    Tow car: 1987 Subaru Brat 4x4
    http://www.fmcowners.com/mbbs22/phot...asp?albumid=77

  8. #28
    Join Date
    May 2007
    Location
    Dixon, CA
    Posts
    84

    Default Conversion to 5spd or 6spd better for Duramax?

    Quote Originally Posted by BigRabbitMan View Post
    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.
    Stephen H.
    BigRabbitMan
    1976 FMC Motor Coach #1046
    Formerly 440, now LBZ
    Rear engined w/4 wheel independent suspension.
    Tow car: 1987 Subaru Brat 4x4
    http://www.fmcowners.com/mbbs22/phot...asp?albumid=77

  9. #29
    Join Date
    May 2007
    Location
    Dixon, CA
    Posts
    84

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    Based on the discussion in this thread http://www.thedieselpageforums.com/t...ad.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.
    Stephen H.
    BigRabbitMan
    1976 FMC Motor Coach #1046
    Formerly 440, now LBZ
    Rear engined w/4 wheel independent suspension.
    Tow car: 1987 Subaru Brat 4x4
    http://www.fmcowners.com/mbbs22/phot...asp?albumid=77

  10. #30
    Join Date
    May 2007
    Location
    Dixon, CA
    Posts
    84

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    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,
    Stephen H.
    BigRabbitMan
    1976 FMC Motor Coach #1046
    Formerly 440, now LBZ
    Rear engined w/4 wheel independent suspension.
    Tow car: 1987 Subaru Brat 4x4
    http://www.fmcowners.com/mbbs22/phot...asp?albumid=77

  11. #31
    Join Date
    May 2007
    Location
    Dixon, CA
    Posts
    84

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    Quote Originally Posted by BigRabbitMan View Post
    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,
    Stephen H.
    BigRabbitMan
    1976 FMC Motor Coach #1046
    Formerly 440, now LBZ
    Rear engined w/4 wheel independent suspension.
    Tow car: 1987 Subaru Brat 4x4
    http://www.fmcowners.com/mbbs22/phot...asp?albumid=77

  12. #32
    Join Date
    May 2007
    Location
    Dixon, CA
    Posts
    84

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    Quote Originally Posted by BigRabbitMan View Post
    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 ...
    Stephen H.
    BigRabbitMan
    1976 FMC Motor Coach #1046
    Formerly 440, now LBZ
    Rear engined w/4 wheel independent suspension.
    Tow car: 1987 Subaru Brat 4x4
    http://www.fmcowners.com/mbbs22/phot...asp?albumid=77

  13. #33
    Join Date
    May 2007
    Location
    Dixon, CA
    Posts
    84

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    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.
    Stephen H.
    BigRabbitMan
    1976 FMC Motor Coach #1046
    Formerly 440, now LBZ
    Rear engined w/4 wheel independent suspension.
    Tow car: 1987 Subaru Brat 4x4
    http://www.fmcowners.com/mbbs22/phot...asp?albumid=77

  14. #34
    Join Date
    May 2007
    Location
    Dixon, CA
    Posts
    84

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    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.
    Stephen H.
    BigRabbitMan
    1976 FMC Motor Coach #1046
    Formerly 440, now LBZ
    Rear engined w/4 wheel independent suspension.
    Tow car: 1987 Subaru Brat 4x4
    http://www.fmcowners.com/mbbs22/phot...asp?albumid=77

  15. #35
    Join Date
    May 2007
    Location
    Dixon, CA
    Posts
    84

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    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 .........

    Stephen H.
    BigRabbitMan
    1976 FMC Motor Coach #1046
    Formerly 440, now LBZ
    Rear engined w/4 wheel independent suspension.
    Tow car: 1987 Subaru Brat 4x4
    http://www.fmcowners.com/mbbs22/phot...asp?albumid=77

  16. #36
    Join Date
    May 2007
    Location
    Dixon, CA
    Posts
    84

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    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.
    Stephen H.
    BigRabbitMan
    1976 FMC Motor Coach #1046
    Formerly 440, now LBZ
    Rear engined w/4 wheel independent suspension.
    Tow car: 1987 Subaru Brat 4x4
    http://www.fmcowners.com/mbbs22/phot...asp?albumid=77

  17. #37
    Join Date
    Sep 2001
    Location
    Ft. Wayne, In.
    Posts
    537

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    Great story! Keep us updated!
    Dave, N9LOV
    Member #242
    Dave's Diesels:
    Sold June, 07 '82 1/2 ton 4X4;340k miles
    '97 2 Dr Tahoe, Intercooled,
    Kennedy ECM, 4" Exhaust
    '02 GMC

  18. #38
    Join Date
    May 2007
    Location
    Dixon, CA
    Posts
    84

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    Quote Originally Posted by DieselDavy View Post
    Great story! Keep us updated!
    The 440 is now out! Yeah!!
    http://travel.webshots.com/album/579...UJYCC?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.
    Stephen H.
    BigRabbitMan
    1976 FMC Motor Coach #1046
    Formerly 440, now LBZ
    Rear engined w/4 wheel independent suspension.
    Tow car: 1987 Subaru Brat 4x4
    http://www.fmcowners.com/mbbs22/phot...asp?albumid=77

  19. #39
    Join Date
    May 2007
    Location
    Dixon, CA
    Posts
    84

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    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.
    Stephen H.
    BigRabbitMan
    1976 FMC Motor Coach #1046
    Formerly 440, now LBZ
    Rear engined w/4 wheel independent suspension.
    Tow car: 1987 Subaru Brat 4x4
    http://www.fmcowners.com/mbbs22/phot...asp?albumid=77

  20. #40
    Join Date
    May 2007
    Location
    Dixon, CA
    Posts
    84

    Smile

    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.
    Stephen H.
    BigRabbitMan
    1976 FMC Motor Coach #1046
    Formerly 440, now LBZ
    Rear engined w/4 wheel independent suspension.
    Tow car: 1987 Subaru Brat 4x4
    http://www.fmcowners.com/mbbs22/phot...asp?albumid=77

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