98 Z28 A4 with 51,000 miles. I change my oil/filter every 3000 miles with Mobil 1 5w30 without fail and no doubt in MY mind this is beneficial to me.

flushed/refill transmision with a NEW FILTER at 40,000 miles.

WHAT ABOUT THE DIFFERNTIAL FLUID? never did anything with this and I really don't understand how this works.

How often should the differential fluid be changed and is there an issue like the transmission with replacing a filter. Sorry for be so stupid but I am concerned the differential fluid is been abused.

AND Anybody know the best way to go about geting a tranny cooler installed?

 

rear diff fluid...

usually goes something like 75K-100K miles before any change needed..

I went with 75-90 amsoil when I did a fluid change and test.. You shouldnt need to do it but in case you want to, get the following:
1 rear diff gasket
2 qts rear diff fluid

Its really simple.. just remove the rear diff bolts, remove cover and let fluid drain..
clean surface of cover and rear diff... use new gasket.. then tighten the bolts.... (there is a specific order in that you keep going across when you tighten them..)

at the top of the rear diff is a bolt that you can remove to add fluid..

takes 1.5- 1.75 qts...

The synthetic stuff I used had the limited slip additive already in it so i didnt need to add any..


as for tranny coolers.... I used the B&M Supercooler Transmission Cooler, 24000 GVW, 11" x 6" x 1-1/2" (got it from thunder racing) when I had a 4L60E.. I spent some time under the car looking for the best possible place to mount the cooler.. essentially the cooler will "splice" into the existing tranny lines.. its not hard.. I had a harder time finding a perfect spot to mount the cooler itself.. I ended up making my own brackets near the front but still protected from any debris that may be kicked up...

good luck..

 

for your differential just pull your cover and replace the gasket and refill.i had mine filled with synthetic last time.if you race it occasionally id recommend changing it once a year.these things are delicate.

 

The owners manual says to initially change the diff. fluid at 6000 miles and at certain intervals after that...check your owners manual.

 

The manual for the 02, says to check it. It doesn't need to be changed. I have been driving for 53 years and have never changed rear axle fluid. Never had a problem with any rears either. How is going to get bad?

 

so bear with me, I'm not the most technical guy when it comes to these things:

the rear differentila fluid as posted here is actually the rear axle fluid as per the last post, right?

Well at 31,000 miles when i bought my Z28 I barely got it home and found out the rear axle was bent. Had the dealer replace the axle then so HE WOULD have to put new Diferntial Fluid in there THEN????

another stupid question, so the differntial fluid lubricates the axle, correct?

Thanks in advance and I appreciate the toleration of my ignorance. I am just **** about fluids and changing everything that is beneficial, like Synthetic Oil, I am a huge fan of oil chnages and Mobil 1 Syn less then every 3000 miles