[jayceenj]

Hi guys!
2005 CTS-V, Black on Black
66k miles... Just serviced the rear differential (factory, I believe) for the first time, and since then, I'm getting a slow speed, grinding/rubbing sound, on tight turns. Not ALL of the time, but fairly regularly. No whine at highway speed, either before or after the service. I followed the CTS-V FAQ, bought two bottles of AC DELCO 10-4016 75W-90 (the "grape" stuff) and the proper limited slip additive. Any idea what could be going on? I haven't modified anything else since the service. FAQ said fill it till it ran out, it took all of the LSD additive and one and three quarters of gear oil. I've probably put 100 miles on since the service, and it doesn't seem to be going away.

 

[darkman]

You probably need more of the additive. I would drain some of the existing fluid and add some more of the additive (GM#88900330).

The fluid you listed cross references to GM part number 88900401, which appears to have no additive. GM part number 88862624 on the other hand already contains some of the additive. In any event, it is not uncommon for a particular differential to require more of the additive. The noise caused by insufficient additive comes from "stiction" from the limited slip clutch plates as they resist the slippage needed for cornering. The noise is annoying but causes no damage to the differential.