I have been struggling with a leaky pinion seal on my 489 diff for years. I have had the seal swapped twice and it still leaks....drips even while sitting.

I am pretty sure it's the pinon seal as I can see the stream of skunk oil coming down from the pinion. I don't think it's the carrier seal. Since I have had the deal swapped twice by a shop that has a good reputation (even with classics), I am thinking there is something else afoot here.

I am thinking maybe the yolk itself could be grooved in such a way that it isn't sealing? Or is it more likely the mechanics really don't know how to swap this seal correctly? If you were in my shoes, would you just plan on ordering a new yolk and doing the work yourself? I have a buddy who has the correct angular torque wrench and knows old cars very well...

If I did want to order a new pinion seal and yolk, any suggestions on WTB and what all I'd need?

Here are the relevant specs:
- 1973 Charger - original 8.75" 489
- was open diff, now has Auburn sure grip
- ring/pinion set was changed to 3.55 years ago - OEM yolk (not sure which spline)
- not sure of the u-joint size but I am thinking the bigger 7290 (what would have a factory 400-4bbl 727 car had?)

I am new to doing work on the rear diff and I am frankly a bit gun shy with mechanics. Any insight would be greatly appreciated!

Have to pull the Yoke and get a Speedy Sleave. Also get a new seal. Problem solved.

Anybody have the part number for the one to fit my application? I am trying not to have to pull it apart and then order parts.

This car does have a pretty stout motor so I was wondering if this would be a good time to just swap the yoke with a stronger one. I am not sure if these tend to be the weak link in the drivetrain..

It's possible that it may not be the yoke if the yoke is not grooved or scratched., but the way the pinion seal was sealed on installation.
When putting in the pinion seal it's good to smear some rtv in the area that the pinion seal butts up against. This prevents a lot of leaks. I would ask the shop if they did this.

If you have been struggling with it for years then why not fix it correctly and be done with it? Drop the pig out of the rear end and get it up on a bench where it can be cleaned and examined. If there are damaged parts then replace them. Otherwise, just put it back together with good parts and eliminate the oil leak. The whole job only takes a few hours if you have the correct tools. If you don't have the right tools then find a local shop that does this kind of work and have them take care of it for you.

So we thinking a speedi-sleeve and a new seal will fix it? At this point, I am hesitant to take this to a mechanic since I have had this done twice already...

I can get the right tools to get the pinion nut torqued down properly. I really don't want to pull the whole carrier out if I don't have to. I don't have any other issues/noises/vibrations - just the leak.

It’s a 489 and nobody has mentioned the god-forsaken crush sleeve. If the sleeve was eliminated with a solid spacer during the last rebuild great, but if it still uses one the correct fix involves removing the carrier, the diff, and the pinion for a new sleeve or spacer.

Sorry, but that’s the nature of the beast. You can attempt to just replace the seal and return the pinion nut to its exact location, but if you don’t get it right you are on borrowed time.

Good point. I ordered the crush sleeve eliminator kit along with a new seal and speedi-sleeve. Anything else I should need?

I was in the process of writing almost the exact same thing but stopped to do something more pressing. The yoke has been off twice for seal replacement and who knows wether the crush sleave was even replaced when the r&p was changed. I agree 150% that the whole thing should come apart. Sorry

What else will I need to buy aside from the aforementioned parts?

when installing the yoke on the pinion, apply a little rtv on the splines to prevent any wicking that may appear to be a seal leak.
also, if the seal has a garter spring facing the pinion, pack that area with wheel bearing grease to prevent the spring from popping off the seal when it's being installed.

If I really have to pull the entire carrier, this is getting a bit beyond my expertise. Is there a good book on the 8.75 rear I can reference? Now I'm looking at inner/outer axle seals and a carrier seal and???

This diff only has maybe 3000 miles on it and I know for a fact all the bearings were replaced. I am really trying not to get into almost a full rebuild here.

Factory Service Manual is what you need.

Where the rebuild and the two subsequent pinion seals all done by the same "mechanic"? Don't go back to him.

I got the factory manual in PDF and started looking it over. The diff was rebuilt around 15 years ago by a shop that specialized in drivetrains. The seal started leaking years later at which time I had another shop (closer to home) re-do the seal twice.

I'd like to learn how to do this but I am worried this will spiral out of control if I have to tear down the whole rear nd, pull axles, etc.

Listen To what the man is telling you

I've even been known to add a bit of sealer behind the washer

Has the vent been checked to make sure it is not plugged solid?

Good idea! I've got a Ram cab&chassis that took a couple of years to start leaking, discovered the vent nipple wasn't drilled!

How bad does it leak? 6" spot in 1 day? 1 week? 1 month? 1 year? How often do you need to add fluid? Maybe a drip pan is a reasonable option.

You’ll have to measure the circumference of the Yoke. Parts store should be able to fix you up. Also, dab a small film of grease on the rubber seal so it’s not dry when you start down the road. A dry seat will most certainly be the cause of future leaks. Of course as was mentioned pulling the pig and getting it on the bench is the way to go.