I'm doing my rear differentials tomorrow. Bought RP 75w140 synthetic. Do I need to add the LSD additive to RP?

 

The Royal Purple website says no. Chrysler additive is mainly zinc and phosphorus. Adding a few extra ounces of additive won't hurt it if your worried.

 

Thanks LongBed.

 

No....no additive is necesary with RP.
Don't even add any extra.
Al.

 

I didnt add any extra. Put 2 quarts in and called it good. It was about 1/2 inche below the hole.

 

Let the diff tell you if it wants extra.

I use RP in my Grand Cherokee with Vari-Lok lockers front and rear that require additive. With just the RP in them, they will chirp-chirp a little on tight turns and when turning in reverse, so I add about half a bottle in each instead of a full bottle of additive and they shut up.

Go with straight RP first, since it has additive in it. If the diff makes any noise or binds at all when turning, then add a little bit of friction modifier at a time until it stops.

Since I have an Auburn LSD in my Ram, I use conventional lube in the rear which does not have friction modifier in it, so I add a full bottle...

 

Changed the diff fluid. Running smooth, no chattering.
Also did complete tranny fluid exchange using the return line trick.
I've done just a pan drop the last couple years. Felt good changing
everything this time around. Thanks to the info I've gleamed here.