Odd Hmmwv Transmission leak

[vitamink]

So i've essentially fixed the majority of the leaks i can find and my m1025 is running great. I have noticed that when i let the thing sit for a while i lose tranny fluid like crazy. As long as it's running consistently, it seems to hold it all in and it dipsticks right at the hash marks (warm). If i let it sit for a couple of days there will be significant leakage underneath, however the dipstick (cold) shows way high on the tranny fluid, about 3x what it should have. I can then start it up and run it until warm. A recheck with the dipstick once warm will now show that it's bone dry. Any ideas? Is there some sort of "one way" valve that is defective sending all the fluid in the cooler to the transmission, filling it to capacity, and then spilling out the overflow?

I'm using valvoline Dexron VI synthetic as i was told its the best, but it's getting kind of expensive. I'm not losing/burning oil, losing steering/brake fluid, this is the last issue to tackle...before something else pops up.

 

[dilvoy]

The fluid from the cooler is draining back. It can siphon back and almost entirley drain the trans oil cooler. You might have a leaky dipstick tube seal where it enters the trans at the right front corner just above the trans pan.

 

[vitamink]

Thanks dilvoy! Ill be calling kascar tomorow

 

[pigfoot63]

I would check the transfer case level and see if it was over filled. The front seal in the transfer may be bad allowing the fluid from the transmission to enter the transfer. Check your air filter box to see if you have transmission oil in it. Also your cooler in your case may be leaking.

 

[Retiredwarhorses]

first of all, where is it leaking from? hose the entire area down with brake cleaner...it has to be clean to find the source, it very well could be a tcase cooler loop broken, but the symptoms dont sound right. check to see if at the top of the Tcase the Vent tube is connected and if that is the source.if its not connected,thats where it can come from, if it was connected your Diffs, Geared hubs and Air box would have the fluid instead of it leaking on the ground. easiest way to see if your cooler loop is broken is to take the fill plug out of the T-Case, be prepared with large drop basin to catch quarts of tranny fluid if in fact its a broken cooler loop...the loop can be bypassed.
I had this same issue on a customer truck a few years back....it toasted his tranny in the Process.

the system work likes a big loop, it comes out of the tranny, to the Tcase, through the Tcase cooler, back out the other tube to the Tranny cooler, out the tranny coller and back into the Tranny....its a complete cooling loop...but in no way should you have any fluid on the ground. you have to isolate the source first, but like I said, take the fill plug off the tcase first.

 

[vitamink]

TheHummerguy, are you thinking it's this then?

http://www.flashoffroad.com/features/Tc ... ampire.htm

 

[Retiredwarhorses]

Yep....

 

[vitamink]

Crap.

I hope that isn't it...it seems complicated. I was able to take a quick peek and look up the part on the TM that it appears to be leaking from. It looks as thought it's coming from the where the "transmission modulator" meets the case. It's leaking down the side to the pan it then travels forward to where the pan contacts the black shroud and then down the outside of the shroud to the lowest point where it drips to the ground.

 

[Retiredwarhorses]

those leak too....there is an O-ring on the Modulator. just make it easy and check the tcase fluid level, there is no way to over fill a tcase...unless its sealed and getting fluid dumped into it from the tranny. its a 1min check. all you need is a large crecent wrenh or correct sise socket.

 

[Jeepsinker]

Did you guys ever get this issue resolved? It could also be that the torque converter is losing prime over time and draining back into the case/ pan, which would cause it to overflow from the vent. Consequently, when the vehicle is restarted the converter sucks all the fluid from the pan leaving it nearly bone dry. Seen 4L80 transmissions do this a few times.

 

[vitamink]

If that is the case, what would i need to replace?

I purchased a new trans fluid fill tube, an o-ring and a new modulator o-ring. I am no longer leaking from those 2 areas so yay me. I'm still leaking where the silver trans pan meets the black shroud thing. Essentially, 2/3rds of the the trans leaks are fixed.

 

[Jeepsinker]

Ok, so now the front seal is leaking it sounds like. The transmission will have to be removed, torque converter slid out, and the front seal ( pump bushing too) replaced. There is an o- ring on the pump shaft that can get knicked, or just fail from age and allow a slow leakdown. Really no way to check if that is the problem other than tearing it all down.

 

[xmiltm998]

I have the same problem with my trans and figured it was the front seal. I just keep adding fluid and offroading the **** out of it lol, I guess I need to tear into this soon before it leaves me stranded.

 

[hummer4x4guy]

A suggestion for anyone who drains the transmission on a 3 speed, there is a reusable gasket for the transmission. Off hand right now I dont have a part # but I did buy mine from www.laneautomotive.com

 

[Jeepsinker]

If it is a pump seal, and you let it leak very long, the pump bushing will weld itself to the torque converter and spin in the pump housing much like a rod bearing spins in an engine failure. If that happens you will need a new front pump half. I would suggest replacing the pump bushing with the seal regardless of whether it has spun or not because a worn bushing is the cause of the leaks more often than not.

 

[vitamink]

Does anyone have part numbers for the parts that need replaced? I'm about to do this thing and want all the parts on hand or ordered! Thanks for the help

 

[Jeepsinker]

Best way to get the parts is to go to a transmission shop and just ask for them. Trans shops keep these parts in stock because they rebuild these transmissions regularly.

 

[Jeepsinker]

And I would bring the whole transmission to the shop and let them change it and the bushing at the same time unless you have experience doing it. There is also a large o ring or gasket between the pump and transmission case that will have to be replaced because the pump will most likely have to come out of the transmission. Then there is the pump puller and the pump installation tool... Best option is just to pull the trans and bring it to a shop. Believe me I've been doing it for years and I've seen a lot of people screw up perfectly good transmissions trying to save a buck. You will save a lot of money doing the removal and reinstall yourself at any rate.