Can someone ID my rear end?

[86square]

Just wanting to knw if it's stock on my 86c10 2wd 5.0 700r....


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[hatzie]

From the 1985-1991 parts book Searched on AZ3...   

1985 C1 AZ3 3.08 8.50 11.15 X 2.75 W/G80

1985, C1 (1/2 ton 2wd), AZ3 (axle code), 3.08 (3.08:1 ratio), 8.50 (10 bolt truck),  11.15" X 2.75" Drum Brakes, WG80 (With G80 Gov Loc).

[86square]

so that means it has been replace since my truck is a 86?

Also I found the codes in my glove box and it had GU4 for rear end wich is a 3.08 same as u listed but different code
Thanks!


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[zieg85]

so that means it has been replace since my truck is a 86?

Also I found the codes in my glove box and it had GU4 for rear end wich is a 3.08 same as u listed but different code
Thanks!


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Early model 1986 would have been built in 1985 so it is probably original to the truck

[1967KaiserM715]

Does the glovebox have G80 as an option? Differential lock. If it doesn't then no the axle is most likely a replacement. If the glove box does list a differential locker then the axle is most likely original. It's common to see parts of one year continued into the next, especially if the parts would be identical.


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[86square]

It does have g80 option
I'm just wondering why isn't the GU4 code stamped on it and the AZ3 is and that one is not on the glove box


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[zieg85]

It does have g80 option
I'm just wondering why isn't the GU4 code stamped on it and the AZ3 is and that one is not on the glove box


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That's easy.  GU4 is the ratio alone, AZ3 gets specific as hatzie shared

[86square]

Oh ok thanks a lot for the explanation now I knw what I have!!
I'm also getting ready to change the oil in it any u guys recommend?


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[hatzie]

GU4 & G80 are RPO (Regular Production Option) codes for the actual chassis.  AZ3 is the axle build code stamped at the axle assembly plant identifying the axle not an RPO.

Model years and calendar years are two different animals.  Production for next model year begins somewhere between May and September of the current year.  2018 models will be available for sale as early as July of this year.  You could easily have a 1986 C10 built in September of 1985.

The original oil was 85W90 but you can use 75W90 gear oil. 10 bolts take around 2-1/2 quarts.  Don't get oil with limited slip additive and don't use synthetic gear oil with the Eaton G80 locker.

I would put a GM Allison 29535617 magnet out of the way of the gears on the cover or in the bottom of the diff to catch any iron in the oil.

[86square]

Great info thanks a lot
I happen to have a gallon of 80w-90 it says for limited slip top off only I'm guessing I should fine right?

I'll be ordering a magnet that's a good idea never taught of that
Thanks hatzie


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[hatzie]

GM started putting magnets in the bottom of the axle sometime in the late 1980's or early 1990's.  You don't even need to glue them down because the cover and housing are made of Iron.

If it says "for limited slip top off only" it has limited slip additive in it.  Don't use that stuff with the Eaton G80 Locker unless you want to find out why they call them gov bombs.  Limited Slip Additive will make the Eaton Lockers chatter and blow up.

Straight SAE 75W-90 GL5 Gear oil or SAE 80W-90 GL5 Gear oil is pretty cheap and it's just what the Dr. ordered.  The GM lube in the below TSB just has a pretty GM label for which they charge a premium price. WalMart Supertech Gear oil in the right SAE grade will work just fine.

Please note I took the liberty of underlining and using BOLD typeface for the important sentences of the TSB text body below.
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.  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.
 

[Rattler12]

Before opening your post, I had a good chuckle at it's title