Replacing transmission seals and gasket.....again.

[Ewr101]

I replaced the speedo bullet o-ring and seal, shifter shaft seal along with a new pan and gasket today on the th350. Did this a couple months ago but still had some leaks that started to get worse so I thought I'd start from scratch again.

Found the new aluminum pan had cracked in the front drivers side corner. Decided to go with a steel pan and be EXTRA careful not to over tighten the bolts. The gasket is the extra thick, silicone or rubber with a steel core one from Moroso so I hope this will be the last time I have to take the pan off for a long while. (Filter is new too) Verified the pan was straight with a steel carpenters square, cleaned all mating surfaces with brake clean on a rag and even washed and rinsed the gasket in dawn to make sure it was free of oil and dirt. Fingers crossed on the pan being done now!!

The shift shaft seal and speedo were pretty easy the second time around. The right tools sure make things easier. Filled it up and went for a ride and all was well performance wise, we'll see if there's any fluid on the ground in the morning. Wish me luck!

Quick FYI- An office chair roller mat makes a great garage floor protector. I got one under each vehicle. Easily clean up and removable to hose off outside the garage.

Have a good Easter weekend everyone!

[Ewr101]

Well I still have a leak. Nothing near as bad so I think the pan is sealed up. I believe the shifter shaft seal is my issue. Thank gawd the pan doesn't need to be dropped or even drained to replace it.

I've see people say they've installed 2 seals in a row and that has helped them. Anyone done this or have any tips to make a good leak free seal on the shifter shaft?

[cleszkie]

Check your breather. If your breather is partially or totally clogged with years of oily dirt build up, the tranny can develop high internal pressure which can cause otherwise good seals to leak. This is internal pressure that can not be relieved through the dipstick tube.

[YoungPup1977]

I always pull the pan off and take the linkage apart when I replace the shaft seal, but again that is the way I do it.....making sure the shaft itself does not have wear or a burr on it creating the leak....most likely when you beat the seal back in you are folding the outer part of the seal into the case....

How are you removing the shaft seal with the shaft in place ?

[Ewr101]

There's a specialized tool that is sold at NAPA to remove the seal. It threads into the rubber portion of the seal and then you screw in a bolt that presses on the shift shaft to pull the seal out. There's also a tool to help install the new seal included but it's nothing special, a properly sized socket would do the same thing. Works like a champ though! I did apply a bit of Vaseline to help the seal slide onto the shaft so hopefully it didn't roll.

Where is this breather located at?

[YoungPup1977]

Originally Posted by Ewr101

Where is this breather located at?

On a Th350 there is a vent, not sure what is being schooled on a breather....if the vent is clogged in some way, ATF will come out of the fill tube....not buying in on the leak being caused by pressure not being released from inside the trans....but maybe I am misunderstanding the concept.....

[cleszkie]

Originally Posted by YoungPup1977

On a Th350 there is a vent, not sure what is being schooled on a breather....if the vent is clogged in some way, ATF will come out of the fill tube....not buying in on the leak being caused by pressure not being released from inside the trans....but maybe I am misunderstanding the concept.....

Whatever your thoughts are about that vent/breather, just make sure its clear. Its good, easy insurance. GM put it there for a reason. I attached a pic of my old 4x4 TH350 with the vent/breather circled.

[Ewr101]

Breather tube seems clear. Ran some twisted wire down it an inch or two till it bottomed out a few times and there was no debris on the end of the wire. Did this a few times and never got the impression it was clogged so that's good.

Shift shaft seal looks to be the only leak on the transmission and it's not too bad at all. Wondering if the shaft itself is worn out and even a new seal is still just a hair too little. The shafts aren't that expensive but I might live with it like this for a while. I'm a little tired draining and refilling the dang thing! Plus I've never dealt with the innards of a transmission besides changing the filter. They're a mystery, wrapped in a riddle, inside Pandora's box.

[simicrintz]

Shift shaft seal-say that five times fast!

[YoungPup1977]

I did say it 5 times, but the shift shaft seal apparently is still leaking....

[simicrintz]

Originally Posted by youngpup1977

i did say it 5 times, but the shift shaft seal apparently is still leaking....

lol!