I have a 71 RS, 350, 4sp and a leaky rear main. The bearings were replaced, the end play is proper and my mechanic has put 3 rear seals (2 piece) in over the last 6 months. Is there a replacement 1 piece? or is there a "trick" to get it to not leak.

You sure that's where the leak is coming from?

Silicone??

Yes, had the engine out of the car for bearing replacement and to correct end play of the crank, put the new seal in and it started leaking immediately.
I needed to use the car (my daily driver) so the next chance I had, the engine was lifted and the seal replaced with a different brand of seal, same result. 30 days or so... and we did it again, different brand, scrupulous installation, and leaking again.

What did the surface of the crank look like? Wrong seal?? Maybe crank still walking too much. I dunno but someone here will have some more suggestions.


Did you use silicone on the ends of the seal and a light film where cap bolts to the block?

Scored sealing surface on the crank chewing up the seal?
I can't explain why else 3 seals would fail so quickly if they were installed properly.

What is the seal's part number?

Did he put the seal in Backwards?? The inner edge lip of the seal " The part that touches the crank" should face forward...if you know what I mean.

Also, are you sure your 4-speed isn't leaking out of the front main drive gear retainer and dripping down inside the bellhousing? Pretty common with overfilled 4 speeds.

Check the back of the flywheel...if it's dry then it's not your main.

Thanks for the replys, I'm going to check all suggestions this weekend.
Thanks again.

There is a special "crank saver" rear seal that puts the lip in a different area from the factory seal so it rides on virgin area. In addition to a small amount of silicone on the end of the seal halves and cap (especially at the corner chamfers) as previously suggested, I also like to offset the ends of the seal halves slightly so seal parting line isn't in line with the block parting line.

And don't over torque the oil pump bolt.