M998, 6.2, 3 speed, lost power and fluid leak from air filter!!

[Lobovianna]

Hello everyone, cheers from Brazil!
I have a 1986 M998, with 6.2 and 3 speed for 4 months now (all fluids changed and hubs checked).

While daily driving yesterday, it started loosing power as if there was a "clutch" problem or something similar. Revs went up but it would move slower and slower every time until almost not moving at all! I stopped it and pop the hood, noticing red fluid coming from the air filter case. I waited for it to cool down a bit and drove home (1 mile ride from where I was) to park somewhere safe - it rode fine.
I will look at it closely this weekend and was wondering if you guys could give me some light on this problem!
I read here on SS about two possible problems to check: 1) Vampire t-case (broken cooler loop) or 2) front seal in the transfer may be bad allowing the fluid from the transmission to enter the transfer.

Any of these is more common in this specs' M998? Tips on where should I start? I have basic mechanical skills and ZERO people with good HMMWV knowledge here in Brazil
Many thanks in advance and kind regards, Felipe

P.S. Attached a pic of my HMMWV in action here!

 

[NDT]

Sounds like vampire. Empty transmission and overfull transfer will confirm.

 

[BLK HMMWV]

Agreed.
once you open the inspection plug on transfer case it will be very obvious.
if your getting red colored fluid out of your air filter housing it's even more obviously you have a broken cooler loop (Vampire Problem)

 

[Retiredwarhorses]

Sounds like vampire. Empty transmission and overfull transfer will confirm.

yep...don’t drive it till you open the fill plug on the Tcase and it drains down.
then fill the trans back up
tyen bypass the cooler loop...

 

[Lobovianna]

Thanks a lot folks!
I opened the t-case and it was overfilled. The oil coming from air filter was actually coming from a vent line right behind it and not from inside it.

 

[cajadao]

But, i believe, that's exactly what happens when you get the 'vampire t-case'.
The cooling loop cracks and dexron is pumped into the tcase. It gets full then there is no else to go, but into the t case air vent... then into the air cleaner .

 

[Lobovianna]

My T-case seems to be the NP218 (pics attached). Is it common to see the t-case vampire in this model? Thanks again!!

 

[Lobovianna]

yep...don’t drive it till you open the fill plug on the Tcase and it drains down.
then fill the trans back up
tyen bypass the cooler loop...

Bad news here :-/ T-case was overfilled (I drained the excess), Transmission was low on fluid, BUT the t-case was already bypassed (pics attached)! Any ideas on possible issue? Any other ways where transmission fluid goes to the t-case when already bypassed?
Thanks a lot and cheers from Brazil

 

[DREDnot]

Off the top of my head, I would think that a leaking trans output shaft seal could do the same thing sending ATF downstream

 

[Gear Report]

Had this exact thing happen in my m1038. Everyone screamed vampire, but that was not it at all.
The transmission filter pickup tube is sealed to the bottom of the transmission by an o-ring.

When that o-ring gets old the seal fails, the transmission sucks air and ATF. That causes foaming in the transmission... Which overflows via the vent line. The path of least resistance in the vent line is back to the transfer case. The ATF won't go uphill to the airbox until the t-case is completely full.

So, transmission is low, t-case is over-full, and airbox is leaking ATF. Everyone thinks "vampire", but I think that is usually far less likely than a bad o-ring.
In this case, I'd put $ on the o-ring.

 

[Gear Report]

Oh...and un-bypass the t-case cooler after you have changed the o-ring and driven a while to verify the fix.
I just published an article about this... https://gear-report.com/humvee-diy-maintenance-hmmwv-transmission-vampire-repair

 

[Lobovianna]

Thanks a lot for the inputs! Will try do all that this weekend!

 

[Lobovianna]

Oh...and un-bypass the t-case cooler after you have changed the o-ring and driven a while to verify the fix.
I just published an article about this... https://gear-report.com/humvee-diy-maintenance-hmmwv-transmission-vampire-repair

Thanks a lot for the inputs! Will try do all that this weekend!