NEED HELP Isolation of Driveline Noises

[therealsethallen]

So, my rear end is acting up. In the morning when I leave my house, I get to the end of the street, and take the same left turn that I do every day. But recently I've heard a little groan from the rear end. It's not obvious but you can certainly feel it. I replaced it with new 75-90 Synthetic on Labor Day. It didn't do this prior. This is a limited slip diff and I did not add any Limited Slip additive, which I think I should have. Secondly, I've got a harsh vibration going on and a little rattle, usually happens when I'm costing or slowing down. It's coming from the left rear. Everything looks decent, the endlinks feel fine and I had the truck up in the air the other day to change out the front brakes, and I lifted the back to check out the noise. When I shook the wheel there was the usual amount of play.

Lastly I should add that for the last week I have been heavily trailering, which I usually only do two or three times a year come camping season. I've been hauling an open car trailer with a Cavalier Race car. on it and I'm doing it again this weekend.

Any ideas welcome. Thanks.

 

[Sparky]

Which gear oil did you have? Some have the additive (friction modifier) already in it. I don't really recall what style of limited slip that is though, whether it actually needs it or not. Clutch-based yes, gear-based (like the one in my Camaro) generally does not.

 

[Mooseman]

It needs that additive if it's not already included or you will have the shuddering.

 

[therealsethallen]

I used my local NAPA's house brand 75-90 Synthetic. Don't recall ever seeing that it did contain a friction modifier. I totally just forgot it was limited slip.

 

[mrrsm]

Here's the Dope on this Stuff:


...and for the other Members and Readers interested about WHY this Goo is needed...

 

[therealsethallen]

Update. One U-Joint, Synthetic 75-90 the ACDelco Friction Modifier from my local Chevy parts desk noise has subsided.

The knocking I heard while coasting, parking brake shoe fell off in the rotor. Removed for now pending installation of a new set when I can get myself into my buddy's warm shop.