rear end oil?

[1986GN]

ok after reading some posts here iam not sure i used the right oil,i used synthetic and the gm additive on my stock posi unit question is should i change over to non synthetic? i have not noticed any problems but would like to avoid any damage to my baby

[Keller]

Eaton really recommends natural lubricant and the additive.

Technically, when using the synthetic you should not use the additive.

How many miles are on the car? Is is ever raced? Has the rear ever been rebuilt? (i.e. New clutches) How often do you change the fluid?

[1986GN]

104k on the car i just did the spring cleaning recently i have owned the car a short time also i dont go to the track but i do get into it on the street but iam not a hard core racer

[PaCemkr86]

i use any 80/90 brand as long as it has the GL5 additive in it

[monzaz]

I have opened 100's of 30 40 and 50 year old rear diffs with fluid that looked like it had NEVER been changed. Almost every gear set that was in the rears that were circulated...Meaning driven with in the last 1-2 years were absolutely fine as far as where goes. Synthetic is superior to Mineral base as far as friction goes...BUT the Posi units we use are FRICTION type unit exception is the Lock right , Power trax, Detroit locker and True Trac type units (gear to gears type units ) These you can use synthetic no problem. The others rely on clutches and cones that grip with friction and pressure. So too much slippery oil will prevent normal locking or eratic behavior of the unit.

Use any weight oil but the GM limited slip additive will ake the unit run the way it should. Yours having 104K could be getting loose all depends on the type of driving. Alot of grandma tight turns and the units will be warn pretty good. If it is freeway and alot of striaght miles. You could be ok for a while yet. It is not hard to change the clutches on the factory GN posi units and I can get you Brand new sets if you all need them. Jim