Converting early gas MH to Duramax? Possible?

[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/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.

[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 ...