Rear main seal replacement on 71 M-20 four speed.

[Rick Church]

I have a messy seap from the rear main seal on my 71 four speed. I have removed a main drive shaft before so I think I can do that again. Is there a previous thread or link to this procedure? My 71 GM shop manuals do not go into any detail. I've been told that the old seal pries out and the new seal is pressed in place. I'd appreciate any hints or guidance on this job before I get started.

Thanks in advance,
Rick in Tennessee

[George Romano]

Re: Rear main seal replacement on 71 M-20 four spe

Remember to mark the driveshaft at the diff end as well as the trans end (if you remove the joint) so it goes back the same way. There is (was) a yellow paint dot on each piece at the U-joints.

The rear seal just pries out, and the new one can be installed with a few light taps with your favorite hammer. Lightly grease the seal before putting the shaft back in.

George Romano

[John H.]

Re: Rear main seal replacement on 71 M-20 four spe

Also, use some sealer on the O.D. of the new seal where it seats in the recess in the extension housing.

[Rick Church]

Re: Rear main seal replacement on 71 M-20 four spe

I have the chassis and overhaul manuals for the 71 but there isn't anything on pulling the rear shaft out. There is one paragraph about the seal replacement. Am I to understand that the rear shaft just pulls out and after the seal replacement that it just slides back into position? What about gear alignment and marking of the shaft before removal? Am I making this harder than it seems? I also understand that the drive shaft doesn't need to be removed to do this job. True of false?

Rick

[Craig S.]

Re: Rear main seal replacement on 71 M-20 four spe

Rick - I am guessing Bill and Steve provided the answer you seek, but due to the server problems earlier are unreadable. Yes, the yoke slids off the splined shaft once the driveshaft is removed. Then pry out the seal, and clean the seal seating area well with brake cleaner. Use a light coating of sealant on the seal cavity and carefully and evenly drive in the seal, after first wiping a light coating of oil or white lithium grease on the seal lips. I usually lightly lube the yoke od as well, and install....Craig