Rearend oil & limited slip additive?

Posted By: T/A CARe

Rearend oil & limited slip additive? - 03/20/11 06:50 AM

I'm putting a 4.56 limited slip chunk in my 8 3/4. Primary use will be street. What oil wt. should I use (and why)?

Also, what's a good limited slip additive? Is the additive Auto Zone sells any good?

Posted By: ireland383

Re: Rearend oil & limited slip additive? - 03/20/11 11:03 AM

Quote:

I'm putting a 4.56 limited slip chunk in my 8 3/4. Primary use will be street. What oil wt. should I use (and why)?

Also, what's a good limited slip additive? Is the additive Auto Zone sells any good?

As far as additive I used Amsoil's Slip lock from Napa and for oil a GL-5 rated 80/90 will do.

Posted By: Kern Dog

Re: Rearend oil & limited slip additive? - 03/20/11 11:07 AM

Make sure you use the HYPOID rated oil too. It includes friction modifiers.

Posted By: torkrules

Re: Rearend oil & limited slip additive? - 03/20/11 03:03 PM

I've found the Royal Purple Max Gear works really well and it has the additive already there. I tried Lucas without the additive and at times the rear end sounded like there was something rolling around in the trunk everytime I turned a corner.

As for the viscosity....whatever the gear manufacturer says or the FSM says. Failing that I would go 75/140 to be safe.

Posted By: Pacnorthcuda

Re: Rearend oil & limited slip additive? - 03/20/11 03:57 PM

Quote:

Make sure you use the HYPOID rated oil too. It includes friction modifiers.

Not true. "Hypoid" refers to the cut of the gears. A "hypoid" lube (like GL-5) has specific extreme pressure additives, meant for ring & pinions--nothing to do with limited slips.
A friction modifier is required for the limited slips, and some lubes have them in it, some do not.

Posted By: ahy

Re: Rearend oil & limited slip additive? - 03/20/11 04:14 PM

In terms of viscosity, OE called for 90 weight, now normally 80W-90. 75 or 85W-140 provides more high temp protection and more "cushion" at lower temps and likley causes a bit more friction and HP loss. Some racers have experimented with lighter lubes for slight ET improvments... I don't have a spare to throw in if mine breaks in an "experiment" so I'm running 85W-140 for the better protection as recommended by the builder of the rear. I've also used Autozone limited slip additive with good results (8.75 clutch type sure grip).

Posted By: RapidRobert

Re: Rearend oil & limited slip additive? - 03/20/11 06:51 PM

Quote:

In terms of viscosity, OE called for 90 weight, now normally 80W-90. 75 or 85W-140 provides more high temp protection and more "cushion" at lower temps and likley causes a bit more friction and HP loss.

, Many choices & I'd think synthetic would b better (for all apps?) but I will defer to the rear end guy on that & some have the additive already in it & yes it's needed

Posted By: NITROUSN

Re: Rearend oil & limited slip additive? - 03/20/11 07:53 PM

Quote:

Quote:

Make sure you use the HYPOID rated oil too. It includes friction modifiers.

Not true. "Hypoid" refers to the cut of the gears. A "hypoid" lube (like GL-5) has specific extreme pressure additives, meant for ring & pinions--nothing to do with limited slips.
A friction modifier is required for the limited slips, and some lubes have them in it, some do not.

Thats exactly right. A lot of companies say compatible with limited slip differentials. That does not mean the additive is in it. I buy all mine direct from the ford dealer parts department. Very good prices.