It seems Mike above is suggesting the neoprene seal is better and if that's what he's saying I agree with him 100%. I found some very old rear main seals in the attic last year, but I'm not sure they'd still be ok to use. They've been there over 35 years. I think they're the old asbestos fiber seals, but I'm not 100% positive. They would have been bought in 1977. I used the neoprene seal in mine...when I got the engine there was no evidence it had ever been disassembled and it had a neoprene seal when I took it all apart. It also showed evidence of leaking, so I compared the seal I removed from it with a brand new one. You can see what I found in the attached image. The edge on the new one sticks out 1.1mm further than the old worn one, so it shows this seal wears out over time. Was that enough to let it leak? I'm certain it was. Here is what I did and it has worked for me: 1. I cleaned up the crank area which rides on the seal with 600 followed by 1000 grit sandpaper until it was nice and smooth. 2. I cut strips of self-adhesive foil tape until I could tell the thickness was going to push the seal out of the groove by .006~.008. This as I recall was two strips laminated on each other. I wanted to be sure the new seal made decent contact with the crank surface. Using a 1/2" piece of common copy paper (.004" thick) I could tell the new neoprene seal didn't fit quite closely enough without shimming it a bit. In other words, that piece of paper didn't have much resistance. 3. I cleaned the back side of the new neoprene seal and applied those strips carefully to just the bottom part...not the part on the sides of the seal. Then I checked to be sure the metal rod inside that neoprene seal wasn't going to be sticking out too far now. Turned out I needed to grind a tiny bit off both ends of one seal piece using a Dremel tool and a very small bit. 4. Then I assembled applying some aviation gasket sealer to the part of the seal that fits in the groove. No leaks now.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
