CME's01S8

Gents,

Getting ready to change out the infamous output shaft seal on my 01 S8. Left cat is covered in gear oil. :-( 1st question.... How long can these things be driven with that leak?

2nd question.... Can I use a synthetic 75w-90 GL-4 gear oil when I do my refill? I know GL-5 can't be used due to it destroying synchros.

Was planning on using a valvoline or Mobil 1 synthetic.

Can u fine gentleman provide me some insight?

Thanks!

Chris

silverd2

They can go long periods with a leaking seal...I know one case where the owner never changed it, years ago and still no diff issue.
The lower edge of the leaking seal is well above the bottom of the sump, so the diff continues to drench itself in oil even when it's low.

Any quality 75/90 full synthetic gear oil is good...the diffs are pretty bulletproof already, compared to transmissions. I've got Amsoil SevereGear in my center diff (the absolute best gear oil available) and Mobil 1 the rear diff.

PS...If it was me, I'd choose Mobil 1 over Valvoline.

CME's01S8

Silver,

Good to know as I am not sure exactly when I can get to it.

That's what I thought. Figured as long as it was GL-4, should be good. Lot of these synthetic fluids say they are both GL4 and GL5 compatible now. That concerns me a little. Need to find one that's GL4 only.

Thanks so much for your thoughts Silver.

Chris

Prospeeder

Its because it was the sulfur in GL5 that ruined syncros. Now they did away with the sulfur and they are GL4 and GL5. Using any newer synthetic gear lube will be fine.

JoePGT5S

Why would the center diff have syncros? Isn't that just a manual transmission thing?

CME's01S8

Thanks so much for the explanation. Makes it easier to buy now. Any of u guys use the liqui-moly brand gear oil? They sell it in the European section at NAPA. Seemed like decent stuff. Only came in GL-5 though.

omarcarbomb

I finally got myself an S8 yesterday(still have the old A8 just not looking so sexy next to its big brother)

Of course it needs some work and the based on how black and smokey the drivers cat is looks like the dreaded S8 output flange seal issue.

I login and find this is the top thread - Coincidence?

I appreciate all of the good discussion on the gear lube.

I have read a few posts that Audi re-designed the output flange and the seal so that you need to get the old seal or replace the flange because they match.

Is this true and if so how do you know if you are buying newer or older seal if they didn't change the part number?

Or better yet if you decide to pay the extra to get the new flange and seal how do you know you are not just putting in the same old flange and wasting money?

JAA 4.2

Don't know about the new seal/old seal story. I bought the seal and changed it on my A6 4.2 (nearly identical trans) and all was good. It wasn't that big of a job...took maybe 3 hours. It never leaked in the 50k after I changed it out.

silverd2

I put in the new type flange and seal to match.

The new type seal has an extra lip that rides inside a groove cut into a otherwise-pretty-much-the-same flange (labyrinth seal). The flange is also designed to close the gap a bit between the flange and the diff housing. The whole idea is to prevent outside grit/dirt from entering the seal from the outside...the seal surface itself is exactly the same as the old type flange/seal.

http://forums.quattroworld.com/a8/msgs/56848.phtml

12K miles after I installed it, it was leaking again...it's more than the seal design that makes these tend to leak...the design of the rear bearing seems to allow a little too much movement (built in movement for heat expansion) and/or wear to allowing even more slop with age >>

http://forums.quattroworld.com/a8/msgs/83473.phtml

omarcarbomb

That is a lot to digest.

I wish a best way to proceed seemed obvious but it doesn't.

You finally got the new re-designer shaft and seal and it failed sooner.

I can see you don't need a new cover but it is possible that getting the cover with the seal in it from factory might matter. This is the re-design kit the dealership was originally promoting. Maybe there is a reason they did this other just more money as they have been accused of.

I read some posts about seating the depth of the seal properly mattering.

I know you have repaired this 3 Times now.

If you had to do it all over what would you do?