What type of rear in oil should I use?

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Eric1998

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Hey,
What kind of rear end fluid do you guys recommend?
I have a 98 1500 extended cab with 150k miles on it. I had this truck for about three years (and I put about 10k miles on the truck during this time) and I don’t know if the previous owner has ever changed the oil. So I figured I should change it.
 

1994_GMC

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i don't know if yours is just a plain open or posi.. in all my stuff open diff vehicles i've ran 75w90, and in my posi diff i use the same with the posi additive from napa.
 

df2x4

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The factory service manual calls for GL-5 80W-90. With NO friction modifiers under any circumstances with any factory carriers. DO NOT use any friction modifiers or "posi additives" with a factory G80 locker. There's a GM service bulletin floating around about this. It will cause unpredictable locking and chatter. ACDelco part number 10-4051 is what I use, it's free of any additives.

https://www.amazon.com/ACDelco-10-4051-GL-5-80W-90-Axle/dp/B007Q10F3S
 

Oldblue98

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Hey,
What kind of rear end fluid do you guys recommend?
I have a 98 1500 extended cab with 150k miles on it. I had this truck for about three years (and I put about 10k miles on the truck during this time) and I don’t know if the previous owner has ever changed the oil. So I figured I should change it.

  • GM Said:
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.
 

someotherguy

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i don't know if yours is just a plain open or posi.. in all my stuff open diff vehicles i've ran 75w90, and in my posi diff i use the same with the posi additive from napa.
No posi ever came in these trucks. It's a locker (Eaton Gov-Loc.) Fortunately other members have posted the info direct from GM about NOT using any additive in these differentials.

So for a GMT400, the answer is the same either way: open or locker, no additive.

Richard
 

Tachyon

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It seems like the best way to consistently get the right stuff is just to go to a GM dealer parts counter and ask for the right stuff for your vehicle. A lot of other places seem confused about friction modifiers with GM rear ends.
Anyway, get the GM synthetic fluid that the parts counter recommends and you'll be fine for any weather and any driving conditions.
 

someotherguy

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It seems like the best way to consistently get the right stuff is just to go to a GM dealer parts counter and ask for the right stuff for your vehicle. A lot of other places seem confused about friction modifiers with GM rear ends.
Anyway, get the GM synthetic fluid that the parts counter recommends and you'll be fine for any weather and any driving conditions.
Or just don't depend on what any "place" suggests and go with what the factory says, which is gear lube with no friction modifier...this is already well-established.

Now if you want to go synthetic that's your choice; synthetic was not factory fill on GMT400* rear ends. Plain old 80W90 GL-5 specification to be exact. The asterisk is in the case of a 3500HD which is Dana 80 equipped, that takes synthetic 75W140.

Richard
 

Tachyon

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Or just don't depend on what any "place" suggests and go with what the factory says, which is gear lube with no friction modifier...this is already well-established.

Now if you want to go synthetic that's your choice; synthetic was not factory fill on GMT400* rear ends. Plain old 80W90 GL-5 specification to be exact. The asterisk is in the case of a 3500HD which is Dana 80 equipped, that takes synthetic 75W140.

Richard

WTF do you think a GM dealer parts counter is going to do? They're going to look up your vehicle, by VIN, and give you the GM recommended gear oil for the specific rear end installed in your vehicle.

As for synthetic, what are you, one of those "all oil is the same" Luddites? Or did you just not know that synthetics weren't in wide use other than in the Corvette two decades ago when that truck was produced? Just because it wasn't factory then doesn't mean you shouldn't or can't use it. They didn't sell the trucks with premium tires either, do you tell people that putting better tires on their truck is stupid? Or should they only use all season Uniroyals made in 1999?

The fact is that synthetic gear oil is proven better in hot, cold, towing, and performance conditions. Period. And considering how seldom you actually have to change it, it's stupid not to upgrade to it.
 
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