Final Transmission/Differential Fluid question

[Dave Hord]

I have decided decided on the brand of oil I'm going to use in both my
transmission and rear differential. However, after buying the rear diff fluid I
thought "hmm..let's check the manual".  The audifans archives said 75w90
synthetic gear oil for the rear diff...but my owners manual says SAE 90.

So which is correct?  Car is a 1989 Audi 90 quattro.

-Dave


For the archives:

Possible brands of oils you could use for your Audi's tranny and diff:

Redline Oil -> http://www.redlineoil.com -> Seems to be the list favorite.
Check for your particular car, but it appears that MT-90 is the preferred oil
for the transmission, and just a 75w90 synthetic for the rear differential.
Many listers are happy with this product.

AMSOIL -> http://www.amsoil.com  ->  A few listers are using this product with
no problems.  Amsoil has two lines, the regular synthetics and the 'Series
2000' synthetics.  Series 2000 is their 'race' synthetic.  Amsoil suggests
their 75w90 is appropriate for both Audi manual transmissions, and Audi rear
differentials. The only listers who contacted me about Amsoil were happy about
the product...I believe all who did are using the standard synthetics.

Royal Purple -> http://www.royalpurple.com -> Not much in the archives about
this stuff...a little bit on their motor oils.  In gear oil the Royal Purple
75w90 is appropriate for audi trannies and diffs.  It exceeds the GL-5 rating.
No listers that I know of are using Royal Purple in their trannies or diffs.


All usual disclaimers apply...I'm not responsible if any of the above melt your
transmission.

-Dave

------------------------------------------------
89 90q  purrs like kitten...okay, a LOUD kitten.
http://home.the-wire.com/~spokes