Transmission Upgrade on M998

[ogrove]

I have an M998. 6.2L engine almost done with rebuild. Planning to add a turbo charger (purchased from BMI, 6-5liter.com). Also planning to upgrade the transmission from the original 3-speed to a 4-speed (purchased from Monster Transmissions). I am aware that I will have to purchase a transmission relay/wiring harness. The new transmission is adaptable to the engine, but the transmission housing is about 3/4" longer than the original 3-speed. Will this cause a problem during re-installation? Will I have to reposition the TC bracket and adjust front and rear drive shafts? Does anyone have experience with this upgrade?

 

[86humv]

What model 4 spd ?

 

[ogrove]

What model 4 spd ?

It's a reman GM from their "black beast" lineup.

 

[MattNC]

Looking on their website it looks like its a 4L80E. If so, you will need more than a few changes correct? I'm thinking cross member change, drive shaft changes, electronic controller, etc. There are a list on the main HMMWV forum here on steel soldiers.

 

[ogrove]

Thank you. I had trouble finding a post initially, which is why a started a new one. There is a very detailed breakdown in the following link that I found through another Steel Soldiers thread (in case anyone else is looking).

4L80-E Conversion - G503 Military Vehicle Message Forums

 

[Mogman]

I assume you made sure they knew you were going to mate it with a HMMWV transfer case yes?
3/4" sounds a little low for the difference but I have not done this conversion.
I would also assume a factory 4 speed cross member would be helpful, but if is really only 3/4" difference the original shafts should not be a problem.
And of course you have to install a 4 speed shifter and linkage, and you will need a little more than a harness, you will need a TCM and it will require at the MINIMUM a TPS (throttle position) and engine RPM input, so you are going to have to install a TPS on your IP, it is somewhat of a PITA.
I always have to build/modify the cross members because nobody makes them for the conversions I have done (Duarmax/Allison 1000 and 6L80)
The 6L I did was 7/8" longer and the shafts fit just fine.