I am hesitating on changing the differential fluid. I have the G-80 locker and the owners manual, says not to use" friction modifiers".I also would like to use Valvoline Synthetic 80-90 GL. I have
40,000 miles on the truck, and have no troubles with the differential. I have never changed diff. fluid before, so this is a new job for me. Thanks, Andy
It's a simple job. You can use the synthetic fluid if you want. I believe that on your diff, it uses an actual gasket, which is good. The synthetic diff fluids will eat RTV, so any of the GM diffs that used RTV as a gasket had to be changed up to regular gasket when using synthetic fluid.
Remove the diff cover bolts, pry off the cover with the tip of a screwdriver, clean the surface of the diff and the cover properly and re-install the cover with a new gasket. Install enough fluid until it comes out the fill hole.....done.
Ian
Does the 2003 not use a drain plug? Maybe it's the 7-5/8" diff that doesn't have one. My 2000 ZR2 had a drain plug on the bottom of the diff, but it was the 8.5"...
Thanks for the comeback guys, but I get different thoughts, about adding the Posi-Trac additive...is it really needed?. Owners manual sez no, dealer sez yes!
Go with what your owners manual tells you to use unless the dealer can show you in writing where GM as said other wise.
Whitelightning
Thanks guys!
The reason the manual says not to use the additive is because it's not a "posi" aka "limited slip". It's a locking diff. It's open until it senses slip and then it locks solid.
The dealer should know better! It's been common knowledge for a number of years now that you do not need the Posi-trac additive for the G-80 rear ends. GM even has a bulletin out about it....tell the dealership to do a search for it.
Ian
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