Hello everyone - I hope someone can help.
Last year I replaced the pinion seal on my 1968 Road Runner 8 3/4 "742" case. After receiving a new seal and then comparing it to an NOS seal, I went with NOS since it was obviously more beefy and the newer one appeared cheap and thin (both the rubber and the metal).
Here I am a year or so later, and the seal is leaking again. Not sure if it was faulty or whether I didn't tork the pinion nut tight enough.
I used a tork wrench and it did not leak until now....
Anyone have any good tips? I plan on installing another NOS seal this weekend. Oh, I do not have a lift. I jacked up the car and used jack stands - which also makes tightening/loosening with a breaker bar a biotch - not much leverage.

How old are the NOS seals? Rubber does have a shelf life.

Not sure on the actual age of the seal, but the rubber portion is plyable and doesn't appear brittle.
The new seal I purchased last year (and returned) just seemed like junk.

When you had the yoke off did you check it fir a noticable groove warn into it from the old seal?

No, I didn't check, but to give some history, I purchased this 742 chunk from Mancini's back in 1997. It was rebuilt with new gears, etc. I put MAYBE 1500 miles on this care since I replaced the center section.

C'mon people, please help me out.

I would check that yoke to see if it has a groove.
Did you get the front of the housing clean and use silicone?

Who is Dr Diff and how do I reach him? Website?

Doctor Diff is the 8 3/4 guru here on the board

Quality Body Shop Drivetrain
110 Division Street, Polson,MT 59860
406-883-4772

doctordiff@gmail.com

good guy to talk with,good service also

Thanks, but the phone number you listed is a fax number.

my bad..sorry,I know I called him ,I will try and track the # down and post it for you

No, problem. I just called Randy's ring and pinion and talked to a guy there about ordering a seal (I have yet another NOS one). He told me they sell the National Oil Seal brand, and when I asked, he informed me that they are "made overseas" UGH! Anyone here recommend a brand of seal to use?

the ones that are made of leather allways leak

dont know why the 742 seal cast 2x as much as the other seals

neoprine seal from napa will work,light duty IIRC but seals better than the leather type

good luck with the leak

I cleaned the front of the housing and mating surface. I didn't think I needed to use silicone. I followed the '68 factory service manual.

That is the correct phone number. If I'm not in the shop, the FAX machine kicks in.

UPDATE...Well a friend with a lift and a compressor helped me out today. I purchased the correct pinion seal from Dr. Diff. last month. Once we pulled the yoke we discovered a deep wear ring around it! This unit was "rebuilt" by Wade at Mancini's back in the mid 90's. It has only 1,200 miles MAX on it. I find it very difficult to believe they used a new yoke when it was rebuilt. Anyhow, We were able to remove the yoke from the 742 case 3:23's I had in my garage, and the yoke which had approx. 90,000 miles on it looked really nice. So...it was really the yoke which was causing the leak rather than the seal - we did replace the seal anyway.

You may want to check the "crapy" overseas seal and see if it places the sealling surface at a diffrent depth than the "NOS" ones. That may alow you to use the "bad" yoke on your other gears. Also one thing to allways check is to make sure the axle vent is clear as it will develop presure as it gets warm and force the lube out .