# REar differential chatter and knock after ring and pinion replacement



## Rainmaker1$ (Apr 30, 2018)

What brand and diff fluid to use 80-90 or 80-140


----------



## PontiacJim (Dec 29, 2012)

Rainmaker1$ said:


> What brand and diff fluid to use 80-90 or 80-140


Don't think the brand of fluid is going to help the problem, sounds like I would pull the back cover off and find out what is making the noise.


----------



## Stephen Blakeney (Dec 26, 2018)

These differentials call for a 75W-140 GL-5 synthetic gear oil. GM part number 89021809. They also call for 1 oz. of GM Limited slip friction modifier. The part number is 89021958. Not sure that the friction modifier with that part number is stll available. 88900330 seems to be the replacement. The friction modifier is actually what helps with the chatter.


----------

