TH350 Leaking
 

My TH350 has always leaked a just tiny bit, but this weekend I noticed the leak became noticeably bigger. After a thorough inspection, I'm relatively sure it's the pan gasket (Again). I removed the torque converter cover and it's dry as a bone in there and there are no signs of leaking from the filler tube or anything higher than the pan. This has been reoccurring problem for a few years now so I think I'm, going to go a different route. I'm thinking of replacing the stock pan with an aluminum one and also install a Moroso rubber with steel core gasket. The pan I'm looking at is made by Mota Performance. It's very similar to a Mr Gasket pan . I'm not familiar with Mota and would like some input on the quality. Any other advice as to seal or not to seal would be appreciated too.

Re: TH350 Leaking
 

I had a leak like that. Thought it was the pan too. Changed it twice.
It was the shifter arm seal.

Re: TH350 Leaking
 

I know what you mean. Usually when you think you have it nailed, it turns out to be something else (Especially in the case of leaks). In this case I inspected around the shift linkage, modulator, fill tube, speedometer cable, and both front/rear seals and don't see any leaking. The only way I will be certain I to replace the pan gasket and keep an eye on it.

Re: TH350 Leaking
 

Mine kept coming back. Finally found it by tieing a narrow piece of cloth around the shifter arm right close to the case.

Re: TH350 Leaking
 

I took mine in last week to have a trans-go kit put in it. It was leaving a mess in my shop, so I told him to seal the leaks too while he had it. $500 later he had to replace the pan seal, shift arm seal, and the seal where the speedo cable goes in. He saved the old seals and showed me why they were leaking. They were all hard. All the pliability of the rubber was gone.

If I were you I would buy these seals and put them in yourself. I doubt they are that difficult, and it would save you a few dollars.

Re: TH350 Leaking
 

While you can install the shifter seal yourself, you need a tool (100 bucks) to remove it without scratching the bore that the seal sits in. Someone tried that on mine. Shifter shaft had to be re-machined so a new seal would work.
250 bucks later no more leak.
The pan gasket and speedo gasket are easier.

Re: TH350 Leaking
 

I would normally do that but I had the transmission completely rebuild less than two years ago.

Re: TH350 Leaking
 

I got the shift shaft seal removal tool from Napa for $7. Worked like a charm removing it except I bought the wrong replacement seal. Model #BK 7769250

Re: TH350 Leaking
 

If your TH350 has an aluminum "bullet" for the speedometer driven gear, they are bad to leak. The replacement is steel and lasts much longer.

Re: TH350 Leaking
 

sKnNyPpY,

Got a part number for that tool? My TH350 leaks a lot too. I've just replaced the gasket and haven't put new fluid in it yet. Seems like a good time to replace this seal as well.

Re: TH350 Leaking
 

The bk# is the Napa part number for the tool. I don't have the number for the seal, the one from Napa I got was wrong so I got it from Transtar locally. Seal was $2. Took me 15 minutes to replace.

Re: TH350 Leaking
 

Transtar also had the steel speedo bullet for $7

Re: TH350 Leaking
 

could be a warped pan