[tjs72lemans]

During my restoration, and rear end out of car, I saw no oil build up leading me to think the seal was bad. I drained old oil, pulled cover off and inspected, cleaned the internals. Sealed up, added new oil and posi (I know) oil. Now over the winter I noticed a small puddle on the floor from a leak. Could this just be from the viscous oil additive and seal up once run and mixed with regular rear oil? Or is it going to need a new pinion seal?

[Stan Weiss]

Originally Posted by tjs72lemans

During my restoration, and rear end out of car, I saw no oil build up leading me to think the seal was bad. I drained old oil, pulled cover off and inspected, cleaned the internals. Sealed up, added new oil and posi (I know) oil. Now over the winter I noticed a small puddle on the floor from a leak. Could this just be from the viscous oil additive and seal up once run and mixed with regular rear oil? Or is it going to need a new pinion seal?

If in fact the rear end is out of the car how do you have it seating? In other word is it seating so that the seal is getting more oil to it than if it was in the car?

Stan

[tjs72lemans]

The rear end is actually back in car with driveshaft hooked up and all wheels on ground.

[Cardo]

It sounds like you will indeed need a pinion seal, or possibly overfilled the rear end. If you do replace the seal, make sure you place a bead of RTV under the nut for the yoke, as the lube will follow the splines and leak from the nut. I always place a very small bead all the way around the flange of the seal where it goes into the housing also as cheap insurance. And above all, DO NOT OVERTIGHTEN THE PINION NUT. Mark it with a paint pen or scratch awl and put it back EXACTLY where it was.

[tjs72lemans]

I never thought of the splines and threads leaking. Maybe that's why my 55 Chevy still leaks after replacing the pinion seal. Thanks.

[rohrt]

I'm going through the same deal. For me its is not coming through the splines and the whole rear was rebuilt about 5 years ago so it should be all new. In my case it depends on how the car is parked. Sometime it leaks bad and others not at all. I have not attempted to fix it. My best guess is maybe there is a grove in the pinion flange from riding on the seal for so many years.

[er455]

Guys the problem is all the seal that are available now are not correct , what is happening is the seal when installed all the way in . the lip of the seal is not in the right place , the fix is to install with a 1/16” spacer or shim so the seal does not go all the way in...

[steve25]

Yes to the above and sometimes in prying out the old seal it’s bore gets scratched in minor way that’s enough to leak, so a thin bead of form-a- gasket can get that potential out of your hair!

[78w72]

i had my 8.5 rear rebuilt by a very good local shop & when i took it home i set it on jack stands while i finished up prepping the underside area to install it... after a day or so sitting at a slightly forward angle i noticed a few drops on the ground from the pinion seal, not the nut. i figured it was just from the fluid sitting against the seal & that it would be ok once installed...

well my dad said if it leaks like that it will leak in the car anytime its parked at a slight angle or even in normal use so i called the shop & asked what they suggested & they said it should not leak at all & they had me bring it back & replaced the seal for free & its been bone dry for 6+ years now. they said it should be dry doing the "tip test" where the seal is pointed down more than it would ever be in the car, just like an engine rear main seal & oil pan should be dry with a tip test.

[steve25]

If it leaks when it just sitting tipped fowards with room temp Gear lube in it, then it will be mess after the fluid gets anywhere close to normal temp!

[Richie Hoffman]

a lot of the seals available are junk sometimes one leaks you put another one in and it’s good just how the quality of parts are now

[er455]

If you make a thin spacer 1/16 to 1/8 and not hammer the seal all the way in it will not leak , you can bend a Welding rod into a circle and use that as a spacer ...

[Formulajones]

Originally Posted by er455

If you make a thin spacer 1/16 to 1/8 and not hammer the seal all the way in it will not leak , you can bend a Welding rod into a circle and use that as a spacer ...

Yes I found this to be true on the 12 bolt rearend.

Basically what has happened with the aftermarket is they are only making the seals for the truck 12 bolts, not the passenger car 12 bolts.

The truck 12 bolt housings have a pinion snout casting that is about 3/16" longer than a passenger car. So it requires a slightly different seal with an extended reach. 20 years ago these seals had different part numbers and were specific to passenger car and truck. Today these seals are combined as one seal with one part number, and that seal is the truck version.

In order to make that work now on a passenger car rearend the trick is a welding rod just as described above is bent around the parameter of the seal flange to space it out slightly, positioning the seal to ride correctly on the yoke. Without doing this every single new seal installed will leak.

However I've only found this to be true with the 12 bolt rearends. I have not found this trick necessary on any of the corporate 10 bolt housings.

[400 Lemans]

https://www.summitracing.com/parts/rat-6109 This is the correct one for 12 bolt car. Read reviews.