Posi Differential???

[961kyle]

How can i find out if my differentials are posi or not? 1994 GMC Suburban K1500 4X4. Reason i am asking is i was told to add the gm additive if they were posi when i change fluid, but i dont know if they are and dont know how to find out. Also is synthetic gear oil the way to go or not? Book says 80w 90 but nothing about synthetic. Parts store has a gear lube called Posi-Lube. Would this work instead of using the actual GM lube figuring its alot cheaper?

[Molson02536]

Originally Posted by 961kyle

How can i find out if my differentials are posi or not? 1994 GMC Suburban K1500 4X4. Reason i am asking is i was told to add the gm additive if they were posi when i change fluid, but i dont know if they are and dont know how to find out. Also is synthetic gear oil the way to go or not? Book says 80w 90 but nothing about synthetic. Parts store has a gear lube called Posi-Lube. Would this work instead of using the actual GM lube figuring its alot cheaper?

Look at your PRO code in your glove box. If you see a G80, then you have a Positraction rear end.

1988-99 models
Do not use synthetic lubricant in axles using RTV sealant.
Synthetic lubricant will chemically attack RTV sealant.
American Axle has only approved the use of Synthetic
Lubricant 75W-90 GM part no. 12378261, as follows:
a. All 8.6 inch rear axles are compatible.
b. All 9.5 inch rear axles built before mid-February 1998
(RTV sealant used to seal cover pan) are not compatible
c. All 9.5 inch rear axles built after mid-February 1998
(equipped with cover pan & gasket) are compatible.
d. All 10.5 inch rear axles built prior to March 3, 1999 are
compatible if axle shafthub RTV sealer is replaced with GM
gasket part no. 327739.

Capacity:
Differential, Front..........1.7 liters
Differential, With 10.5 RingGear Dana Rear..........2.6 liters
Differential, With 10.5 RingGear EX D Rear..........3.4 liters
Differential, With 11 RingGear Dana Rear..........4 liters
Differential, With 8.5, 8-5/8 R Rear..........2 liters
Differential, With 9.5 RingGear Rear..........2.6 liters
Differential, With 9.75 RingGear Rear..........2.6 liters

Good luck and this should help you and others. The best you can do is to do 50/50 mix with 80W90 and Lucas oil additive. We have been using Lucas on the Motor Coach i drive and the rear end in my jimmy has over 350,000 miles.