I hope that no one thinks that this question is too out of place - I could see it going either in this forum or in the tranny/drivetrain forum, and since I rarely ever even look at that one...

Real quickly, I added a TA Performance diff cover this year (to try & strengthen my 9-bolt a bit) & refilled with Red Line synthetic. I figured that would be enough, but no, I'm getting "chunking"-type noises, & I'm fairly sure that they're coming from the rear.

So I stopped driving the car, & this week I bought the little 4 oz bottle of GM's Limited-slip friction additive, but my question is this - will it hurt the diff if I just add that to the existing fluid (theoretically overfilling the diff by 4 oz.), or should I drain a bit of the Red Line gear lube out, add the GM additive, & then re-fill w/ the Red Line to the "full-level hole" in the diff cover?

Obviously, it'd be easier to just add the GM additive, but I don't want to FUBAR my 9-bolt just because I was too lazy to do a few extra steps...

Thanks guys.

 

A little extra isn't going to hurt it but you should drain a little out.

 

Thanks Stephen, that's kinda what my gut was telling me, but it's good to get it confirmed.