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One area in which I lack experience is automatic transmisisons. The HM4L60/THM700R4 was used from 82 to 93 on C3 and C4. I have a question for the early THM700 experts out there.

I am preparing an 82 CE for sale and it's got an intermittant trans leak at the manual valve shift shaft seal in the side of the case.

Is it possible to replace that seal with the trans in the car simply by pulling the pan, filter and valve body then removing the manual shift shaft and changing the seal?

If so, anyone ever done it like that?

 

I did a refresh on my tranny with it still in the car, so yes, its possible :thumbs:

 

I don't know how different the shift shaft setup on a 700-r4 is from a TH350 and TH400, but on either of those transmissions it isn't really necessary to pull the valve body or even drop the pan. The seal itself can't be pushed out from the inside as there is a lip that the seal is pushed up against. If you pull the shaft it is easier to get the old seal out by using a sharp pointed pick or awl. You can get the seal out without removing the shaft, using the same sort of pointed awl or pick. To install the new seal just push it in with a 1/4" drive deep socket of appropriate size.
A real problem that sometimes ends up being a problem is the condition of the shaft itself. If it is rusted or grooved then replacing the seal won't fix the leak. Then you have to replace the shaft, or polish the shaft with emory cloth to get the rust off. It is usually easier just to replace the shaft, they aren't expensive.
Something else you can try is not remove the old seal, just slip another seal over the shaft and seat it on top of the old seal, there is plenty of space for two or more seals. Since the extra seal is further down the shaft the chance of a wear groove causing the seal to leak again are less likely.
I really hate transmission leaks and have spent a great deal of time trying to fix them anyway I can.
Good Luck!

 

Smokehouse---thank you for the good information.