Mysterious Transmission Leak?

[RickTheEngineer]

Hey folks, my M1009 has always had a transmission leak. I run through about 500mL per 1000 miles or so. This is fast enough for me to warrant some concern. I replaced the filter and put a new pan gasket in. I see on the frame on the passenger side sometimes signs on tranny fluid, although It can be hard to tell with all the grime on the road that gets in the way also on the frame. No matter how hard I try, I just cant seem to find the leak. The front end where the cooler lines attach to the radiate are just about perfect with no signs of leaks... Granted, I have no checked the cooler lines all the way to the tranny itself so I do suppose it is possible it can be coming from there too. At the bottom of the bell housing I do see some wetness, and I am hoping the front seal isn't bad. But I would have to pull the tranny off to check right? the rear of the tranny is a bit wet too (kind of all over honestly). I don't wanna waste anyone's time here because I know I should degrease everything and then check to see where it is all coming from, but do any of you know the common places to check on the TH400? Or have a hint on what it could be? Tranny fluid doesn't smell burnt, and when I replaced the fluid it held up well honestly! Got 83,000 on her. Thanks so much everyone! Happy wrenching!

 

[porkysplace]

Change the o-ring on the dipstick tube .

 

[cucvrus]

Also check the breather tube on top of the transmission. If that is blowing a bit of fluid and everything else is fine and not leaking. Just slip a small rubber hose on the vent tube and extend the tube up higher to vent. I had an M1009 that did this and I did the tube extension and it ran like that for many miles/years. Still may be like that.

 

[RAT]

Modulator was always an issue for mystery loss of fluid. Bet the hose is full of fluid.

 

[cpf240]

My ATF 'mystery leak' turned out to be the fiber washer on the transmission drain plug.

 

[Rvitko]

I would check the cover on the governor, rear passenger side toward the top. I had a leak there. Also verify it is not overfilled. I overfilled mine because my driveway has an incline and it would blow out the breather, it wasn't grossly overfilled either, a pint too much.

 

[Matt65]

My leak was the cooler line.

 

[RickTheEngineer]

Hmm interesting replies yall! I looked at the cooler lines, and I didnt see a whole lot, although I feel as though I am gonna need closer inspection... However, the leak seems to me on the passenger side on the leaf spring mostly (which initially I thought was a fuel pump leak, and after replacing it I noticed the fluid was red so it wasn't the fuel pump). Pan is mostly dry, and clean on the transfer case. I am not too sure what I was looking at but there was something round and cylindrical shaped, about 18 inches long by the fuel pump area where the tranny is very close to or connects to. Lots of oil over there! Ill try to upload pics, but I dont have a camera at the moment!

 

[richingalveston]

I believe the only cylindrical thing there is the starter. the fuel pump Is in front of starter and tranny behind. If it is leaking red at the connection between the tranny and engine then it is probably torque converter seals. The coolant lines connect on that side also so it may be a leak in the coolant line and it is spraying on the tranny.

 

[RickTheEngineer]

Hey all, old thread I know, but I wanted to post here instead of cluttering up the forum! I am still trying to tackle this mystery (I have been working on other projects so it's been on the back burner!) I have some pics I wanted to share about the leak that might help us figure out what's going on! Any thoughts? Also as for the starter and leaf spring having some wetness, there could be a small chance it is diesel from the filter assembly, but as for the front driveshaft, bottom of the bellhousing and more I don't have an answer for it. Only other details I can provide is the fact that the spot that the oil cooler line attaches to is dry as a bone, and the diptstick filler tube is dry too. I haven't followed the cooler line, and I could not tell if there was leaks from the upper part, but I would suspect that if it was leaking from up there it would travel to where the fitting are on the tranny? Anyways, thanks for the help guys! View attachment 632476View attachment 632475View attachment 632474View attachment 632478View attachment 632477View attachment 632472View attachment 632473

 

[cucvrus]

Hey no pictures there dude. I am a bit confused. What was or is leaking? Or don't you know yet?

 

[RickTheEngineer]

 

[RickTheEngineer]

I hope they posted this time! And Im still losing a bunch of tranny fluid, just cant determine where it comes from haha, sorry about the mess up on the post!

 

[german m1008]

If it were my truck....I would take a few cans brake cleaner...and clean it and look were it starts again.
Everything else is a mystery advise......

 

[cucvrus]

I can see where it is leaking from. It needs to be removed from the truck and sent out for rebuilding and resealing. It is leaking at every external seal it has. the transfer case is leaking at the shift lever also. So do yourself a favor. Fix it now while the parts inside are still good. The seals are like fresh potato chips (crispy) in that 30 year old transmission. I will not even put a used TH400 in a CUCV anymore without having it gone thru at the transmission shop. It cost a bit now but is a bit less expensive then burning it up and buying transmission fluid. Same as a used CUCV engine. If you are going to put a used engine in at least change the head gaskets and all the other gaskets. It is not worth the effort at this point. The bottom ends are good most times but to freshen up the top end is well worth the effort and cost.

 

[rustystud]

I see the modulator is leaking also. Pull the hose off it and see if any fluid comes out. I also agree with cucvrus. I think it is past time for a rebuild on that transmission.

 

[RickTheEngineer]

Alright yall, I know it's been a while but I took some brake clean to the tranny, and that didn't last long. Here is what happened today. I started the truck for not more than 45 seconds in park just to idle. Turned it off and lost about 500ml of fluid all over my drive way and it was legit pouring out from under the truck. Now I think it was spewing out of the dipstick tube, but I am not sure because I cant imagine it running that violently down the tube without make even a small mess in the engine bay anywhere. Here are some pics, and I am curious on what you guys think? Clogged breather tube maybe? I am trying to investigate, but it's pretty hard to diagnose at this point. Also, how much is a reasonable price for an tranny reseal/rebuild? Everything on it works fine, just leaks excessively, which might be from what just happened today? Anyways, here are some pics for y'all to share a laugh at!

 

[cpf240]

Hole worn into the metal cooling line?

 

[RickTheEngineer]

I actually was thinking that, but the think is that I think the cooler lines go towards the driver side? I might be wrong! But the fittings where the lines mate to the tranny are dry as a bone, so it definitely didnt travel down there! Its leaking right above the starter, and pouring onto the front driveshaft. If it helps, it did not gush out until the engine stopped about 30-45 seconds of idling! Plus since some fluid was coming out of the tiny hole at the bottom of the tranny bellhousing is that the front main seal??

 

[rustystud]

Looks like the input seal is bad. Also check the torque convertor to see if it has a drain plug that came loose.