Diff Fluid

[Mr Red]

Crusin through a parts rag and saw an ad for Differential oil... There was one type for regular and one for limited slip. When I bought my rig, the guy said it had posi's front and rear. Well, the front is definitely posi (both wheels spin when off ground and you spin one side) and I think the rear is actually Limited slip cause I've had both rear wheels spin in the mud and snow.

Question: How can I find out for sure about the rear diff.? And, is there a difference in oils between the limited slip and others? I was planning on changing the fluids in both diffs since it's been ~5 years since they were changed.

Thanks for the help,
<font color=red>David, '86 K5</font color=red>

 

[bigjbear]

First a note: posi is short for Positraction, Chevy's brand name for a limited slip diff (ie.Shure-Grip, Track-Loc, ect). There is an additive that is needed to keep a limited-slip working properly. If you buy regular gear oil, a good quality 80w-90, you can go to your local Chevy dealer and buy the additive. It comes in a tube. You must use either the additive or the special gear oil or your L/S diff will quickly return to one leg status. BTW I use the GM additive in my Auburn Gear L/S in my Monte Carlo with no problems. Jim.

BigJBear '80 GMC

 

[Mr Red]

OK, thanks. I'm still not sure if the rear is limited slip or not. I read somewhere that you'd have to spin one of the rear wheels (while off the ground) really hard to make the posi "kick in" and have the opposite tire spin, to be sure it's a limited slip/posi. So, until I get better info., another question: If I were to use the gear oil for a limited slip in my rear diff, and it's not a limited slip, will that hurt anything? Seems to me that'd be a safe move.

Thanks for the help,
<font color=red>David, '86 K5</font color=red>

 

[Toad]

Most 80-90w oil has special additives in it anyway for limited slip. It will say on the bottle. It won't hurt to use it if your axle is non limited slip.

 

[AZK5]

Lift the axle your checking and get the transfercase in nuetral. Rotate one of the tires by hand. If the other tire turns in the opposite direction it is an open differential. If both tires spin in the same direction then it is some kind of traction device: locker, limited slip or spool. Even a worn out limited slip will turn both tires in the same direction when there is no load on the opposite tire. Otherwise have someone that can identify it look inside the cover.
CB