K10 Suburban - What Differential Oil

[AdrianR]

O All-Knowing Oracles

Methinks it is time to change the oil in both diffs on my Burb (see sig).
What's the best weight/type oil to use and how much does each diff take?

thanx

[iluvmy72]

10W30 *wink*

[rcbildr]

If your burb has the gov-loc option for the rear end, there is an additive you will need. Last time I bought it, I paid around $10 for it at the dealership. Every diesel burb and truck I've had came with the gov-loc. I used 85W90 gear oil and that additive when I change the fluid in the rear end of my Burb.

[68Timber]

Originally Posted by rcbildr

If your burb has the gov-loc option for the rear end, there is an additive you will need. Last time I bought it, I paid around $10 for it at the dealership. Every diesel burb and truck I've had came with the gov-loc. I used 85W90 gear oil and that additive when I change the fluid in the rear end of my Burb.

No additive for the gov-loc:

LOCKING DIFFERENTIAL LUBRICANT (SERVICE INFORMATION) #91-4-109
SUBJECT: LOCKING DIFFERENTIAL (G80) LUBRICANT - (SERVICE INFORMATION)
VEHICLES AFFECTED: ALL LIGHT TRUCKS EQUIPPED WITH G80 REAR AXLE ALL YEARS
Some light duty trucks equipped with locking rear axles (G80) may exhibit rear axle chatter, especially when turning a corner from a stop.
This condition of alternate engagement and disengagement of clutches in differential assembly is usually caused by contaminated axle lubricant.
To correct this condition, drain and refill the rear axle with SAE 80W-90 GL5 (P/N 10950849).

The use of any additive in locking rear axles (G80) is not recommended. Rear axle additives are designed for use in limited slip differentials which are normally installed in cars. All light duty trucks equipped with RPO G80 make use of a locking differential and the use of additives will delay the engagement of the locking mechanism and may decrease axle life.

VEHICLES/COMPONENTS INVOLVED: ------------------------- ---- Some light duty trucks equipped with locking rear axles, RPO G80.
SERVICE PARTS INFORMATION:
Part Number Description ----------- ------------------ 10950849 Lubricant, Rear Axle (1 litre)
Parts are currently available through CANSPO.
WARRANTY INFORMATION:
As specified in Light Duty Truck Maintenance Schedules, locking rear axle fluid drain and refill is required owner maintenance at the first engine oil change. Failure to drain and refill the rear axle as specified may contribute to a later axle chatter condition. Refer to the appropriate Light Duty Truck Maintenance Schedule or service manual, section OB, for further details on change intervals.
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.
© Copyright General Motors Corporation. All Rights Reserved.

[AdrianR]

Thanks Bruiser - I had suspected that a straight 90W oil would be OK but I wasn't sure about the additives.

I guess a PTFE based additive - something like Slick 50 - wouldn't hurt, right?

[68Timber]

No, I'd keep it simple. You have to keep in mind how many of these trucks are resurrected often and easily. Use a name-brand 90W or if you don't mind the extra bucks, fill it with synthetic 90W and forget it.