Getting ready to change the oil and was considering a Diff service. Is it necessary at this time on an 01 Z28 A4 2.73 with 34k miles. Car is not raced or abused, no noises coming from the rear. If I do the service what oil to use and do I need the GM additive.

 

It is recommended that you service your differential every 30k miles,I think... That said, I'm way overdue (bought at 80k - has 117k now, previous owners probably never changed it either from the looks of it) but nothing has exploded yet... Just have to get off my *** and get under the car. If you see the RPO code G80, then you have a limited slip rear differential and you should include the additive. It is to help reduce rear end noise from the limited slip...

 

i think all LS1s have the torsen, not the auburn limited slip. and either way gm recommends using the additive.

i service my diff every 15k. thats the interval for all chrysler vehicles i work on too.

 

I'm pretty sure that '98 and '99 had the auburn limited slip and require the additive.

 

Go to this link, it will tell you how to do the change, what to use, and has detailed instructions and pics.
http://www.bfranker.badz28.com/fbody/lubeoil.htm

 

Easy, slightly more difficult than a oil change.

 

you can get a differential cover gasket for $3 from any of the auto stores, might have to ask for a 1998 or 1999 model. They didn't have it when i asked for my 2002, all the model years are the same.
just undo all the cover bolts minus 1 on each side halfway up, then pry the cover easy on a corner with a flatblade to get the oil to drain cleanly, as opposed to one big splash.
buy a gear oil pump, they're worth it. you will not be able to squeeze the bottle to fill the differential, and will leave more oil in the bottle worth more than the gear oil pump.
1998 had auburn standard which required limited slip additive, and the torsen was optional. From 1999 on the torsen was standard and the auburn was optional.

For fluid, any gear oil that is API-GL-5 rated. Viscosity is basically irrelevent, anything like 75w-90, 80w-90, 75w-140, 85w140 will work. The auburn has "recommended" mineral 80w90 gear oil... they say the mineral oil at that weight provides the best all round performance, and it also requires the limited-slip additive (or friction modifier) because it has clutches.

Helped change the differential fluid on a 1999 ford econoline 3/4 ton van that had 110,000 miles on the factory fill. The fluid came out clean , no stain at all on the inside of the cover. The only problem was the differential would groan sometimes on corners because the limited-slip additive in the fluid had worn out (it was a limited-slip unit). The fluid change with new additive fixed it almost immediately. If you have the torsen then you don't need to use the limited-slip additive, although it won't hurt but using too much of the additive is not good either, for the torsen i would recommend using half the recommended amount of additive all that it does is help keep the diff quiet on slow speed tight corners. but based on my limited experience there's no need to service your differential, the synthetic gear oils they use as initial fill do last their intended 100,000 miles. biggest thing i would check is if you have the auburn or torsen, if torsen then no need, if auburn then a fluid change with additive is probably a good thing.

 

How do you tell if you have the torsen or the auburn? Did I miss this in a previous post?

 

Thanks everyone for all the info. Either way I'll probably do it, seems easy enough. So having an 01 Z28 with a 2.73 which diff is it Torsen or Auburn? sounds like I have the Torsen. Why are they different?

Any recommendations on which oil...I was going to go with Mobil1 and the GM additive.

 

[QUOTE=Adam2001WS6;10353652]How do you tell if you have the torsen or the auburn? Did I miss this in a previous post?[/QUOTE

G80=limited slip=additive.

I buy the additive and gasket from GM for about $15 total. I use M1 75-90 synth and have never had a problem (80K).

 

nope starting 99 they used the torson

 

you may have the auborn or torson but i used the royal purple 75-90 oil and that stuff is great and is full synthetic and already has the additive in it

 

Service interval is less than 30K, I got into mine about 15K and
it was full of shavings from the Torsen.

 

^^^ true mine had some shavings, also the auborn i read in the owners manual says to be changed 7k miles with the additive

 

What's the name of the Additive? I saw some on the shelf at an auto parts place next to the gear oils and it said it was for GM and Chrysler rear ends part nums. #####... I don't remember the part numbers, but it did say Limited Slip Additive something or another. Is there one and only one?

 

Use GM OEM additive only.

 

Yes, you can use that. Everyone will tell you to go to the dealer and get the GM stuff, but its all essentially the same. Ive used the GM additive and trans-x additive found in auto zone and haven't noticed a difference.

 

I would think 30,000 miles is a bit early. Usually 100,000 is recomended. I did mine on my 1995 LT1 M6 @ 85,000 miles and used Royal Purple 75W-90 MAX gear and did not use an additive because Royal Purple is syntheic and already has the limited slip additive. It is about $15.99 a bottle and my 95's rear end needed just under 2 quarts. You will also need a gasket for the diff and black RTV to make sure it seals up correctly. I actually used the website that was recomened above. I did not feel or hear any difference after I did this, I guess the rear end has been good. If I were you I would wait till at least 50,000 miles to do this because it will cost about $50 which isn't bad but it took me about 3 hours with a buddy.

 

this is like saying why change your oil every 3,000 miles when you could change it every 6,000 and be fine. you may not notice a difference but its preventative maintenance, and piece of mind. Id rather spend the ~50 bucks and change it every 10,000 miles just to say i did.

 

Well it is up to the person and their budget. It seems like a lot of LS1 guys are willing to throw a lot more money into their cars for some reason. I guess because they probably have the extra money. But you really have to do a lot of beating on your car to have the rear end oil break down to cause something to break. The bolts fastening the ring gear will break from torque before your oil will break down from driving 50,000 miles and not racing.