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Advice needed on Trans and diff oil change


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Jan 23, 2003
San Jose, CA

When should I change the transmission and front/rear differential fluid? I'm at 60K and it seems like it might be time to change the fluids. I'm confused on which fluid to use in the rear as it says that it is special synthetic for the limited slip.

Also, what about the transfer case- when does that need to be flushed?

Real-world advice please.

I used Mobil 1 75W-90 in the rear and front (GM calls for 80w-90 regular dyno in front). I would not say GMs version is special and most likely made by Mobil anyway. Choice is yours. I used GM Autotrac II fluid for the transfer case..It needs 2 quarts. I did them a while ago, maybe at 30 or 40K. The owners manual, I think, has loooong intervals. I think it only says to check every 15K and add for the diffs and change transfer case at 100K. I currently plan to keep my AV for 200K so did them much sooner in hopes of longevity. Many say its un -necessary.
if you're at 60K I'd just drop the pan, change the filter and refill, quite a few people have had problems doing a flush at the mileage 
I made a point to do it at 50k, but I did everything...all fluids, plugs, wires, etc...just to know evrything was done at 50k...easier for me to keep up with it.
I run Royal Purple in both trans and diff. Its supposed to help them run smoother and cooler, and so far they done just that (y).

60k is long enough,lots will say not needed etc(no service interval on diffs as per manual) but if you can do it yourself its cheap and easy, also use synth. in the front diff.  the poor ol t-case has a service interval of 50,000 kilometers but never gets done and it really needs to be done....
Thanks for the tips. I gotta find a place to do the transmission. Since unsure of the diff changes. I noticed my rear is leaking... Better check that.

if you have a G80 rear you will need to add bottle of addjitive to the mix or it will make noice
moosc said:
if you have a G80 rear you will need to add bottle of addjitive to the mix or it will make noice

I never added that before. Its not a limited slip and does not need it. Its supposed to make a noise when it engages.
I have done all of mine twice already. I do them every 50k to be on the safe side. I am currently at 110k with no issues at all. Be sure to use Synthetic it just seems to work better.