Thread: TH350 transmission question.

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Hope someone on here works on these and can shed some light on a problem we have.

Aside from the engine problems we had on my Son Dan's rpu (which should now be fixed with the new motor) he also had a persistent fluid leak from the TH350 transmission. If the car sat for a few days a puddle would form under it, about in the area of the front of the pan. Since fluid will travel it was hard to see where it was coming from, so we kept wiping it clean and trying to find the source.

We replaced the shift shaft seal, the pan gasket (now using a cork one with a good, thick aluminum oil pan) and still it leaks. There is nothing dripping down from the seal on the front pump, it is dry, however, last night when we were looking at it we see some seepage directly under the large round plate that you remove to get the front pump out. I think this is called the front pump cover.

We had this trans built and then we found we had broken off the tangs on the front pump so we had a local shop replace the pump for us. Is is possible when they put it back they pinched a gasket or seal that goes in there? I have also heard there are flat seals on all the bolts that go around the perimeter of that cover.

I stopped at the transmission shop that did the work the other day and he says this is common for th350s and is called "convertor drainback" and recommended a check valve they sell to go in the cooler line. But the th 350 in my 23 never leaked a drop so I tend to wonder about that.

Any help will be appreciated.

Don

it does sound like the front seal was damaged.

It does to us too, Barb. What makes me wonder is that we had the car running in the shop for long periods of time before we noticed it wouldn't go in any gear, so we had the front pump replaced. During those long periods (months) we never had a drop on the floor, but after the pump was done and he started driving the car the leak started. Coincidence maybe but not sure.

There in no fluid showing dripping down from the seal that goes around the snout on the convertor where it goes into the pump, that is dry. But we see some fluid around the bottom of the large cover that holds that seal and the pump.

Don

it really sounds like whoever replaced the pump pinched the seal.

Don, the front pump on a th350 has a rubber o-ring on the outside of the housing and a gasket where it meets the case. Another source may be,when it was rebuilt the pump-to case bolts washers/gaskets may have been left out.
Brian

Brian:

1) If we remove those bolts all around the perimeter of the front pump housing and remove it, do parts fly out? We wanted to pull the front pump last night to see what the gasket or o ring looks like, but Dan remembered when he tore down a junk th350 we had to use as a mock up tranny that springs and stuff came flying out.

2) When you say the "pump to case washers/gaskets may have been left out" where are these exactly?

Thanks for the info so far.

Don

Don I don't remember any gaskets or seals around the bolts that hold the front cover on...There is a gasket or "O" ring there . You could see if any of the bolts are loose. Taking it apart you could wind up with springs from the clutches depending on how it lifts off. I would bring it back to the guy that did the repair. Sometimes the converter , when at rest will drain back into the trans but shouldn't leak out.

Charlie, last night when we discovered that wetness underneath the cover I got a socket wrench and tried to tighten the bolts. They are REALLY tight, I couldn't even get them to turn a bit.

I probably will end up throwing it in the trunk and taking it back to the trans shop. The guy there has been super helpful and they treated us right the first time around.

Don

Don, The bolts ,that go through the pump and into the trans housing should have gaskets,similar to washers on each.
The front cover you are refering to, is part of the pump housing. When the pump is removed you can see that the pump is 2-piece,as it is bolted together. You can remove the pump,without losing or moving any parts inside,as long as the trans input shaft is pointing upward. These pumps have two threaded holes,opposite each other,and will take a 3/8" bolt to attach your puller to.
Before I'd remove the pump though, I'd wipe off where you think it is leaking ,tip it up slightly on the rear and watch to see if you can find where it's seeping from,Brian

I should say, that the 3/8" holes are "inside" of two of the smaller pump bolt holes

Brian, are those seals that are supposed to be on each bolt visible from the outside when you look at the bolt heads? Reason I ask is I don't remember anything like gaskets on each one when I tried to turn them with the socket.

Don

Don that sounds like the caught the seal when replacing the pump, I really can't believe they didn't fit a new seal when they did the job as that a common place for leakage.

The bolt gaskets are thin black washers.
Some GM trannies have pump bolts with a groove just under the bolt head that accepts an o-ring.
I've taken some apart that have had both installed. Only the proper one should be used on the proper bolt.
Take a bolt out and check it.

Its almost impossible to pinch or knick the large perimeter rubber pump seal when installing. The gasket behind the pump will not cause external leaks.

Check the seal at the dipstick. Oil leaks can seep a long way and appear they are coming from another spot.

Steve, I felt they might have done something in that area or maybe the housing itself had a burr or distortion there that won't seal correctly.

Pugsy, I will pull out the bolt and see if there is a washer/seal like you describe. As for the dipstick, we considered that but he is using one of the new Lokar short stick dipsticks that actually bolts on with a big nut underneath and a rubber seal. If it is leaking it would have to be out of the top part but it also goes down into an o ring seal. The kickdown linkage was glued in so hard he had to pry it off (also a Lokar)

I have two other th 350s in the shop, one B and M and one Jackson Racing and offered one of them to Dan but he reminded me his has the BOP bolt pattern and mine are Chevy. I know they sell an adapter plate but his car is all setup for the BOP so he wants to use it. I guess it will just be a matter of taking it back to the shop.

Don

Don i was referring to the seal where the convertor runs.

Originally Posted by Itoldyouso

Steve, I felt they might have done something in that area or maybe the housing itself had a burr or distortion there that won't seal correctly.

Pugsy, I will pull out the bolt and see if there is a washer/seal like you describe. As for the dipstick, we considered that but he is using one of the new Lokar short stick dipsticks that actually bolts on with a big nut underneath and a rubber seal. If it is leaking it would have to be out of the top part but it also goes down into an o ring seal. The kickdown linkage was glued in so hard he had to pry it off (also a Lokar)

I have two other th 350s in the shop, one B and M and one Jackson Racing and offered one of them to Dan but he reminded me his has the BOP bolt pattern and mine are Chevy. I know they sell an adapter plate but his car is all setup for the BOP so he wants to use it. I guess it will just be a matter of taking it back to the shop.

Don