blitz928

I'm going to be replacing my differential seal on my S4 auto in the next week or so. I've read the archives and the consensus seems to be that Redline 75w90 synthetic is the way to go for replacing the differential fluid when I'm finished.

Is their any other recommended alternatives that would perhaps more readily available at Wal-mart?

I've called the few auto parts stores and they don't have redline and the one speed shop that carries it wants $18 a quart which seems steep. Since the differential requires .9 gallons so I'll need 4 quarts for the job.

I've found Amsoil 75w90 synthetic severe gear for $9 a quart, I assume this would do just fine. Any other options? Tips?

dr bob

Either will be fine for the diff. If you have a limited slip diff, the oil for that is spec'd slightly different. Lots of recommendations over the years on what to mix. I 'tuned' the mixture for 30lbs/ft cold breakaway on my then 40k-old diff using a blend of Redline NS and non-NS fluids. Started tight and worked my way backwards. Using the wrong oil can leave you with minor diff chattering on turns. The way mine is now, it will not steer on my epoxy garage floor if I touch the brakes at all. Just goes straight. LSD must be working!

checkmate1996

pap-parts.com - $10.95 a quart for redline 75w90 or ns

IcemanG17

I use amsoil severe gear in my race 928's....but I've also heard good things about redline too

The race shop I go to rebuilds literally 5 transmissions a week for local racers..& they swear by valvoline synthetic....cheap and easy to find! But I still use amsoil

blitz928

Thanks for the tips, I ended up ordering Brad Penn 75w90 Hypoid synthetic, Amazon had it with free shipping at 10.49/quart. I've heard good things about Brad Penn so I'll give them a try.

http://www.amazon.com/Brad-Penn-Oil-...ecc_rvi_cart_1

Ducman82

i just did the redline in mine, seams to work well.

slate blue

I believe the diff uses straight SAE 90

Greg

jpitman2

I did some research here, and all I got was must meet GL5 spec SAE 90, independent of LSD or not (which I have). Have had no trouble in 8 years after chaqnging it.
jp 83 Euro S AT 52k

blitz928

It does call for that, but the modern equivalent is 75w 90 Hypoid gear lube.

jpitman2

Like I said, just find a GL5 rated 75W90 or 90 straight. I was told that rating is more important.
jp

SharkSkin

I started out with Redline when I first bought my car, and on the rebuilt transmission. On the rebuild, the input shaft seal started leaking. Talked to Doc Brown about it since he's the one that put it together, and he says that he sees more leaks with Redline, his theory is it is TOO slippery and doesn't allow the seals to run in properly. Switched to the Mobil 1 75-90 and the drip stopped. YMMV.

dr bob

Dave, interesting you mention the leaks. Mine was dripping once in a while, and I finally narrowed it down to the bottom drain plug threads. The Redline was working its way through them with the bolt torqued correctly. Pulled it apart, cleaned the drain and the plug threads and used some teflon sealing paste on them instead of Never-Seeze and all seems well again. I did put a Redline cocktail back in. Generally I'll take 'too slippery' as a good thing in a gear case.

SharkSkin

Bob, I agree that slippery is a good thing. It's probably a non-issue once the seal has been run for a while. All seals leak a bit, ideally just enough to keep the seal/shaft interface lubricated. Upon installation of a new seal, there is some initial seepage until the seal and the shaft are broken in. If the lubricant between the seal and shaft is so slippery that the seal cannot exhibit this initial wear that conforms it to the shaft, it will continue to leak.

It may well be the case that putting Redline back in after some period of time will not be a problem. Certainly the fact that you had no such problem with your well-broken-in seals indicates that it is not a problem in every case. I think it is a relevant discussion here since Matt is installing a new seal, but I could be wrong if what Matt is really referring to is a gasket rather than a seal.

Doc B's repeated experiences of having Redline leak like a sieve on new seals, and seeing the problem go away with different lubricant, certainly has SOME cause, some fact-based explanation must account for this. The above sounds plausible, but whatever the explanation I had the same experience with brand-new seals.

Rob Edwards

Greg poured a quart of Mobil 1 into my newly resealed tranny and told me to fill 'er up when I got it home. I have Redline in the GT and haven't noticed any leaks but I haven't been under that car in a while.

SharkSkin

Rob, I don't think it's as much of a problem with old, broken-in seals. Ask Greg about Redline next time you see him though.