1991 M998 6.2 with 6L80E and Auto Transfer Case

[bzbartender]

I recently had a new motor and transmission put in my 2007 Yukon for my son to drive for his first car which he totaled 2 months later so know I'm trying to determine if I can take the complete drivetrain out and with some modifications make it work in my M998. Using the transfer case isn't necessary but if all I need to do is have the drive shafts lengthened or shortened seems logical. Maybe I'm wrong but I figured this would be the place to find out. Thanks in advance

 

[Mogman]

WELCOME to the SS forums!!
I have moved this to a more appropriate forum.
Just to be clear you are talking about a gasser 6.2 not a diesel 6.2L yes?
If so the drive shaft mods would be just a drop in the bucket, you will have to deal with hybrid 12-14V systems, exhaust, engine mounts including cross member, a stand alone wiring harness to include the engine, trans and transfer case computers (you cannot bolt the 6L80 to a HMMWV transfer case) the custom stand alone harness with the laptop program to adapt the ECM/TCM/TCCM will run $1500 or more)
Air intake, radiator plumbing, fan mods, shifter mods.
These are just a few, But I have not done a gasser conversion just a Dmax conversion so I may have missed a thing or two (but I did do a 6L80 conversion using the original Detroit engine)
I would assume by 2007 the gasser would be running a fly by wire accelerator pedal which would need to be adapted.
This would not be a project for the week at heart but would be totally doable although a daunting task.

 

[bzbartender]

My wife just picked me up off the floor after reading that..... Thanks for all the information!!! Extremely useful
Yes it's a gasser.

 

[Mogman]

Oh yes I forgot about instrumentation, the stock stuff sucks, the Dmax conversion I did was an LMM, I re-wired the entire truck and installed all stepper gauges, on the one I am starting now (LBZ) I am going to use the original inst. cluster out of the donor truck as it unlike the LMM does not require a the BCM (body control computer) to feed the inst. cluster, this should same me some work other that completely modifying the cluster and dash.

 

[Mogman]

Here is the build thread for the Dmax, as I stumbled through it, it was however a big time game changer and worth the 7 months I took to do it (I had a regular job then) I also have a fully equipped shop.

How not to install a Duramax in a M998

Well hopefully this will not be the epitaph for this project, I thought a thread with the progress and possible pitfalls that lay ahead might be interesting to someone, constructive criticism, hints and comments from actual experience will be of course welcome. Some of this has been told before...

www.steelsoldiers.com

 

[bzbartender]

Would I be better off since I'm just trying to get better highway speeds to switch out the diff from 3.90 to 3.07?

 

[Mogman]

If you have a M998 then you already have the lowest ratio diffs at 2.56, the A2 has 2.73 and the ECV has 2.73, there are no lower ratio gear available then the 2.56, since you have a 3 speed you could install a 4 speed OD trans (4L80E)

 

[Mogman]

It is too bad you do not have an A2 with a 4 speed to start with, it would be less work to just couple up the gasser to the HMMWV transmission, you could still do it with the 3 speed and that gasser would not mind running the higher RPMs.
You would still need a stand alone harness and the ability to program the ECM, intake, exhaust, water plumbing, fan mods, 12/24V hybrid, but it would be less work.