turbo 400 dies on its last day

[MattNC]

So today was the day to head to get the turbo 400 transmission swapped on the M998. I have purchased and received a level 3 700r4 from Bowtie with all the accessories and it was in the bed of the humvee and ready to head out.

Yesterday I had finished installing the tach from SECO and also added a 12V step down and fuse box for the 700r4 torque converter lockup to run off of. I verified everything was working as plan and all checks of the multimeter were correct with 24V were it should be and 12V coming out of the step down and fuse box.

After checking all fluids per the PMCS I go to pull out of the driveway and watching my new tach and I see it shift into second but then not into third. Third is acting like neutral. All revs, no forward motion. I pull over, check everything out, continue on my way and same thing but now I am starting to lose even second. I verified it wasn't a transfer case slipping out by turning the engine off and going into L then back to H with everything working correct. First gear is good and strong and reverse was strong as well with brisk acceleration backing up a hill. The shift to second is like shifting into neutral and now I never get to third. I checked the fluids again, and I was slightly high on the transmission fluid so I pulled a quart out to be in the lower portion of the hash marks. No leaks were seen anywhere and no noise.

I can't see how my electrical work did it with the turbo 400 not having a controller. Its drives me crazy but at least I have the new transmission in a crate in the bed. My wife claims I hurt the transmission's feelings and it mutinied on me, but I didn't see that in the TM's anywhere! As an engineer by training its driving me crazy especially given I've been driving it regularly with zero issues. In 1 mile it went from no issues to DOA. Fluid was barely warm as well coming out of the transmission. Well, it will be trailered to its swap destination tomorrow, and I'll keep you posted what we find out.

 

[MattNC]

Transporting it is delayed a day or two so I checked the fluid level again and took it down the street. It holds in first gear with no slipping but doesn’t want to shift under throttle to second. If I let up the accelerator it up shifts and second isn’t there. It just freewheels like it’s in neutral. Once it slows down it downshifts into first and moves again. The only thing I changed since the last successful 40 mile drive a week ago was adding the 24v to 12v step down converter off the batteries. I cant see how that would have done it.

 

[TOBASH]

Shifter alignment issue?

 

[Maxjeep1]

Whatever happened you need to make sure that they flush the cooler and lines when you get your new transmission. I had a new transmission installed by the dealership that didn’t make it a block before it failed because they didn’t flush it after my old torque converter failed. Glad it was still under warranty! Turbo 400 is pretty robust transmission and I would be curious what happened. Transmissions confuse me and they were obviously designed by people that are on drugs. That ball goes here and we will put a few more here here and here and we can make a maze of passages to connect them and we can separate the halves with a metal plate and if you want to change the firmness of the shifts drill here and here. Definitely the work of Gypsies!

 

[MattNC]

I took a look again. The shifter works correctly and shifts correctly between all gears including forcing it down into 1 only. Good call Maxjeep about the flushing of the lines, I'll ask for that. The overall package I bought from bowtie comes with a temporary magnetic inline filter as well to help with this over the first 500 miles in case the flushing missed anything.

 

[TOBASH]

It will be cheaper and faster and more effective to just hire a flatbed to bring the HMMWV to your mechanic. Stop worrying about that old POS three speed and start loving life with your new 4 speed. I would replace the tranny cooler at this time. Screw the flush and just change the cooler and the lines. Mine developed a leak at the time of the swap so I replaced the entire stack. Found my radiator had three pin holes and the steering cooler was leaking from corrosion. Just swap it all out brother and live life without needing to look back for the next 20 years.

IMHO

 

[MattNC]

Great advice TOBASH. Being an engineer by training I hate not knowing why something happened! I need to make peace with it. The gentleman doing the work is picking it up with his trailer, we got rained out last night so we delayed a day. He gave me essentially the same advice, things happen and its good I have the new transmission in the bed ready to go!

 

[TOBASH]

Make sure the tranny AND the transfer case are in NEUTRAL if he is dragging your rig behind a tow truck!!!!! Make sure he knows NEVER to place the vehicle transfer case into HL.

 

[TOBASH]

Great advice TOBASH. Being an engineer by training I hate not knowing why something happened! I need to make peace with it. The gentleman doing the work is picking it up with his trailer, we got rained out last night so we delayed a day. He gave me essentially the same advice, things happen and its good I have the new transmission in the bed ready to go!

Being the son of a PE and being an Orthopaedic Surgeon, sometimes I need to remind myself that sometimes fixing something is less productive than just replacing it and moving on.

Feel free afterwards to figure out the failure. Open up the unit and play with the innards AFTER your rig is operational.