Changing Rear Diff Fluid - Do I Use The Limited Slip Gear Oil Additive?

[RochesterMJ]

Changing the rear diff fluid, bought gear oil (75W-90) at the store, guy at the counter says I need the limited slip additive.  I buy it and am now wondering:

 

A)  Do I have a limited slip diff?  How do I know?

 

B)  If not would it hurt if i added the stuff?

 

 

Here's my basics:  91 MJ, LWB, Base model, Auto 4x4 D35.  Street driving, no towing, hope to off-road at some point.

 

Any help would be appreciated

[Blue88Comanche]

safley secure the jeep so it won't roll. jack up the rear of the jeep make sure both tires are in the air, put in neutral, then spin the the tires by hand.. if they go the same direction then its Limited, auto locked, or spooled. if they spin in opposite directions then its open

[Minuit]

I can't imagine the LSD lube would hurt an open diff, it just wouldn't really do anything.

[onlyinajeep726]

I bought some synthetic 75W-90 with the LSD additive already mixed in but I have an open diff.  Says right on the side of the bottle "for use on LSD and safe for non-locking (open diff.) applications."  So to answer your last question, I'd say that's a negative ghost rider... Carry on. :thumbsup:

[RochesterMJ]

I'll have to give that a try Blue.  Thanks for the knowledge guys.