Th350c rebuild or just re seal?

[Taylorb27]

So the front seal on my 84 c10’s th350 completely let go and is leaking trans fluid like mad. It started a block away from home when I gunned it and it’s been parked ever since. Now that I’ve got all my ls swap parts together I’ve decided it’s time to tackle the trans, question is should I completely rebuild it or just put new seals and o rings in it, put a shift kit in and send it? This is all assuming the fluid looks good and there’s not much for clutch material in the pan. A gutless 305 was in front of it so it’s had an easy life and only 74,000 miles (confirmed). Always shifted good just not firm like I like.
The 5.3l I’m putting in will be just a stock motor with plans of a cam swap and tune probably next spring.

What would you do? I’d like to just reseal and do a few valve body mods to keep cost down but maybe I should just shoot for a full rebuild?

 

[Matt69olds]

Remove the pan, that will tell you everything you need to know. If the pan is full of crud, it would be kinda pointless to not go thru it before installing it.

Make sure the converter and pump bushing are in good shape. Don’t just drive a new seal in without making sure it didn’t leak due to other damage.

 

[Taylorb27]

Remove the pan, that will tell you everything you need to know. If the pan is full of crud, it would be kinda pointless to not go thru it before installing it.

Make sure the converter and pump bushing are in good shape. Don’t just drive a new seal in without making sure it didn’t leak due to other damage.

yes the condition of the bottom of the pan is a big factor in what I’ll be doing.

what kind of damage would I be looking for? I guess I should mention that this happened just days after adding seafoam trans tune to it.

 

[Matt69olds]

Look for damage on the converter hub, make sure the bushing isn’t walking out of the pump.

I’m not familiar with sea foam additives. I do know for a fact those seal conditioners (sometimes advertised as stop leak) can cause problems if you leave it in the fluid for too long. While the conditioner will soften hard seals, eventually the seals will soften and swell to the point they kinda dissolve the rubber.

If you use the seal conditioner or stop leak, it’s best to run it just long enough for the seals to soften a bit, then change the fluid.

 

[Taylorb27]

Look for damage on the converter hub, make sure the bushing isn’t walking out of the pump.

I’m not familiar with sea foam additives. I do know for a fact those seal conditioners (sometimes advertised as stop leak) can cause problems if you leave it in the fluid for too long. While the conditioner will soften hard seals, eventually the seals will soften and swell to the point they kinda dissolve the rubber.

If you use the seal conditioner or stop leak, it’s best to run it just long enough for the seals to soften a bit, then change the fluid.

Not sure if the trans tune has stop leak in it but it definitely did not sit long enough to swell any seals before it started leaking bad.
I’m hoping it’s not as hot today so I can pressure wash the bottom of the pickup off and get started on taking the trans out so I can see what’s going on

 

[scenic760]

If you have the time and about $150, you can rebuild with some simple mods to double the strength of your transmission. I just rebuilt my th350c and I have to say it was actually a good experience. Just complicated enough to feel a sense of accomplishment without throwing things across the garage. It was also a great learning experience on how transmissions work.

Now I have yet to put it back in the truck and see it actually work, but I'm optimistic (coming from a pessimist)...good luck whichever road you choose!