mikenews

iTrader: (9)

I have a 98 z28 A4 that I wanna change the fluid in the rear diif. I believe I'm gonna use 75w-90w. My question is what brand of oil and do I have to add additive. I will most defiantly be putting in some sort of synthetic. I have had good experiences with Amsoil products before. What do u guys suggest??? Thanks

3rdgentug

iTrader: (23)

if you have an auburn ( clutch style ) diff. use an additive
if you have the zexel ( metal ) diff. dont use the additive

dailydriver

If you still have the Auburn (the stock unit, if you, or no one else changed it out) in there, DO NOT use synthetic!!!!(despite what ever the manual says) Use a good mineral based gear oil (Torco RGO, Lucas non-synthetic, Shaeffers, etc.) and start with 4 ounces of the friction modifier. Add more if there is still chatter after it is thoroughly mixed.

chicane

Dont use a synthetic... period. Honestly... what do you actually gain from running it ??

Nothing... comes to mind.

Seriously though, you woud gain more from stepping up to an 85/140 or a straight weight 140 than you would from changing over to a full syn. Personally, I am a fan of the parrifin based oil from Schaffer... and dyno based from the like of TORCO... and then add friciton modifier to taste.

mikenews

iTrader: (9)

Where do I get the friction modifier? GM dealer or can I buy some from parts store?

alamantia

iTrader: (10)

either

8a8mfh

iTrader: (3)

GM or ford ONLY.
I had two tubes , 32 oz, of the parts store crap in my first new Auburn and it made all kinds of noises. Called Auburn, they said thats the one question they get 20 times a week, all related to cheap friction modifier.
I ended up getting GM gear oil and ford friction modifier because GM was out.
4oz of the good stuff stopped all the noises.

chicane

I really like the FoMoCo Friction modifier... available thru the deela'