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Rear end locking up.

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Hey guys! New to the group, let me first introduce myself. I finally purchased a 2003 victory red AWD Silverado SS, 115,XXX.


So when I first purchased my truck, I picked it up in Pittsburgh PA, I live in Virginia, total trip after buying the truck was around a 5 hour drive. Probably like an hour after we left the dealership, I stopped for a bite to eat, I take somewhat of a sharp turn and my rear end starts to lock up.

Being 4 hours from home, I let the truck cool down, and I begin my way back home. Again, my truck start locking up, making sharp turns. I checked the differential fluid, it was low, it was very thinned and it smelled burned. Next morning, I drained the fluid, and put in Mobil 1 with the lsd additive. I drive an hour out of town for my birthday dinner, and again it started locking up. I let the truck sit for a couple days (not my daily driver, I have a built civic). I drove the truck a few couple thousand miles and never happened again on long drives. Yesterday, drove 1 and a half hours and started locking up again. Any ideas of what it could be or if it has happened to anyone else?

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Welcome to the site. :cheers: Congrats on finding your truck.


Do you recognize any bearing whine coming from the rear? By "locking up" do you mean that the axles stop rotating, or that the diff locks, like a locking diff will?


The condition of your fluid is sending up red flags. Have you drained the Mobil -1 that you put in it? Or at least sucked some out to check it?


What did the dealer have to say about your troubles?


Best luck brother.

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Well these 10 bolts are junk imo. If it were me, I would get it over and install a tru trac, differential girdle and new bearings. That would be a stout enough diff for any future mods you plan to do. The low level, thin, burnt fluid is definitely not a good sign. Also you don't need any lsd additive since your truck should be gov lock and not limited slip.

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None of the truck lockers use additive. If the truck has RPO G80 (which I think all SS's do, yeah?) then it wants straight gear oil.

The axle may be damaged anyhow, but regardless, the additive is not helping matters. Check out this TSB - funny I was just posting it a little earlier this morning for someone else on a different truck.


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.
Part Number Description ----------- ------------------ 10950849 Lubricant, Rear Axle (1 litre)
Parts are currently available through CANSPO.
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.



Edited by someotherguy (see edit history)
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FYI, GL5 Gear oil already contains friction modifier for use with limited slip.




you are correct, the rear should have G80 limited slip differential.


To the original poster. Are you referring to the front or the rear differential locking up?


It could also be the AWD Transfer case as they are filled separate from the transmission and not typically maintenanced properly. If they are not cared for, They will start Humping as it's been termed which is like its looking and unlocking.


Not sure if you purchased as is or if it had some type of warranty but you may want to take it back and have it inspected if it does have any type of warranty.

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Are you 100% sure on GL5 having friction modifiers, meaning, any and all gear oil in the GL5 spec? And while we're discussing the terminology, does "friction modifiers" mean the same thing as "limited slip additive"?


My only real experience with choosing a GL4 vs. GL5 gear lube is back when I had a Unimog. Mercedes is adamant about not using GL5 in the transmission as it will eat any "yellow metal" parts (syncros typically), but it's fine (and recommended) to use GL5 in the differentials.


I think the GL5 specification and additives meant for limited slip aren't necessarily intertwined, and you can get GL5 gear oil without any limited slip additives. I know some are made with it but I don't believe that is part of the GL5 spec. Many brands say they're limited-slip "compatible" but one that stands out in my mind is Amsoil's mention that if you experience chatter with their gear oil in a limited slip differential, to add their "Slip Lock" friction modifier additive.


Not an expert and absolutely welcoming any elaboration on the subject. If what you say is true then the GM TSB is suspect since they suggest a GL5 gear oil.



Edited by someotherguy (see edit history)
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Most 75/80W 90 Gear oils I personally have come across are Synthetic or synthetic blend. It's hard to find something that is not.


Every thing I saw with a GL-5 rating at the parts store stated it's additive package was sufficient for use with limited slip differentials.


I bought Valvoline the last time I did a gear oil change. I have used synthetic and regular from valvoline. I have also used the mobil 1 gear oil as well as Sta-lube gear oil products. I also know the Royal purple states the same thing with the GL5 product.



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