The Stovebolt Site Forums The Shop Area Engine Shop Leaky TH350

the tranny in my jimmy just wont quit leaking. I have pulled the pan and replaced the gasket a couple of times and the last time i did it, i used enuff blue goo to re float the titanic. Sure enuff, the was a big puddle of red oil the next day or so underneath. I have previously replaced the tailshaft seal and it is ok, and i pulled the tranny out which was a real pain with my equipment and i replaced the seal behind the torque converter. I feel that this is where the oil might be leaking as the dust cover always has a drop hanging from it. Am i missing something? the lines are all new and show no signs of leaks. I just dont really know much about how an auto trann works, or if there is something up front i have missed.

There is a seal where the cast iron pump sits in the case, this generally does not start leaking, it would be from the start if it leaks. Also there is seals or metal washers with a sort of teflon coating on them on each bolt the holds the pump in. One could be loose? The other problem could be a cracked case. The center support for the internals on a 350 have cogs or notches that match the case. If there is alot of load in that area it can crack the case.

A cracked case is most common in a 4X4 when the slam them in forward and reverse alot.

I would not suggest using silicon on any tranny, if the any little chunk gets in the valve body, which controls shifting your done.

What I do is make sure the pan surface is flat, use gorilla snot ( wheather strip adheasive) clean both surfaces. Use the gorilla snot on the pan and adhere the gasket to the pan. This way the cork gasket will not push out and create leaks. Don't overtighten the bolts.

Good luck,

Brent

I'll bet your "selector" shaft seal is leaking.
You know, where the lever attatches. There is a special seal puller/installer tool for this application.

Jim Sgrig

Check-out Piewagon's sugestion on your shifter shaft seal and if you have a plug-in on top of the flange where the locking torque converter plugs in, there is a seal on that connection (I need to replace mine now. Replaced every seal in tranny when I rebuilt it, but that one and guess where it is leaking?). You wouldn't think that seal would ever leak, but it will.

Truck Tinker

Also check out the o-ring on your dipstick tube. I see these leak all the time.

And finally, one thing I've found to cause major leaks is the housing for the speedometer cable driven gear. I know it's a long way from the dust cover, but the inner housing (known as the "bullet") has an o-ring on the outside but can wear an egg-shaped opening inside. This can cause all sorts of leakage.

If I understand things correctly, the "early" parts (I have no idea what year range) were made of pot metal, but later replacement parts were made from steel, which had less of a tendency to wear internally.

Good luck with it...if you replace everything that's been mentioned in this thread, all you'd need is some new clutch packs and you'd have a brand new tranny.

Ray

Check the "O" ring on the fill/dipstick tube. It's notorious for seep leaks, especially if the bracket where it bolts to the bellhousing is broken off the tube, or it's just not bolted on. Later models have a rubber sleeve in that position rather than an O ring, and switching to the later model tube and seal is the best fix. Ditto on the shift shaft seal, it gets forgotten pretty often. Stay away from the Blue Glue!
Jerry

Check the pan itself. I've had problems with leakers on two TH-700's. The pans are made of mild carbon steel and if water ever made it into the trans, it quickly eats out the bottom and creates pinhole leaks that are difficult to repair. The leaks usually occur on the bottom of those stiffening ridges/grooves at the bottom of the pan.

Every sealing point of a TH350 has it's problems. There's an accumulater cover on the right side of the trans that is sealed with an O-ring that tends to leak. I've seen housing cracks around the brass fittings for the cooler lines also. As many others have stated, dipstick tubes are notorious for cracks at the o-ring landing and the spot welded upper bracket.
Scott