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Rear Differential Problems


New Member
Sep 13, 2002
North Branch, Minnesota
I have had my AV in to 2 different dealers,5 times. Relating to a problem with the rear differential.
It seems as if the posi is locking up, and it "pulls" around corners, and also locks up and stops the truck on gravel( I accused the wife of power braking in the driveway, OOPS) ???
I have been told that I needed a Diff. service at 12000 miles, Well that didnt fix anything!,and it cost me $90.00 to boot
I was also told that it was a problem with the ABS controller?
Anybody out there with similar problems and hopefully an answer.
The differentail should never lock up and stop your truck. I would return to the dealer that screw you out of the $90.00 to get it back and make sure they repair the rear end. Thats a warrantee problem for sure.

It sounds like the differential was so low on lube that the thing is locking up. They likely thought that if the gave you the service story and added lube that it would break loose.

Go to the Eaton site and print out the information on the G80 and take it with you. The G80 differential needs no service under normal use. The lube level should have been checked at 7,000 miles.

Good Luck (y)
mnbigpower my old k-5 did this and it would bind up because diff "posi" was bad finally tore completely up and in 1993 cost 650 bucks,... make them go for ride. and get the whole posi unit replaced to correct!!
Problem- On 2 separate occasions during wet weather, the limited slip engaged, but would not release. This happened when I entered a parking garage which has a counter-clockwise direction with some straights. As I turned each corner, the right wheel screeched and hopped until I straightened out. It would only unlock after I changed direction and started down in a clockwise direction.

The dealer performed service on the axle, said fluid was at right level, no excessive metal shavings, and checked and cleaned clutchplates. They mentioned that once in a whle I should go to a parking lot to do a few figure eights to lube them up and keep the parts moving.

I will re-post if it happenes again.
GM sells a small bottle of "posi lube" that will more than likely take care of your problem. It is a friction modifier for lubricating the clutch plates. Every once in a while I would come across a vehicle like that and the "lube" would take care of it. Put it in and drive for a couple hundred miles, it should be gone. If it persists the only thing to blame would be a mechanical failure of some sort.
The differentials in the AV don't use Posi or clutch plates
It is a mechanical locking type [unless it has been changed] AKA detroit locker

that said, it DOES help to add the Posi additive because it is a enhancer even though there are no plates

The way the Eaton system works is by centrifical force which sends a cam into a lock
designed to work under 20MPH only

So you have a trip to the dealer to make
Good luck
The Av uses an Eaton G80. It is a mechanical locker, but it is not a Detroit locker. The Detroit normally is locked, unless there is a difference in load between the wheels, such as turning. When loads are different, two dog clutches on either side of the spider assembly spread apart and the unit unlocks.
Thanks for the update
I haven't seen the diagram on the G80, and assumed because it was a locker, it was the same

My father use to tell me, never assume anything in life--
I guess I assumed, I would never forget that

Boy, I love this place (y)
big power, had the same crap happen with my 2500...just got the thing out of the shop. Replaced front differential. 12,000 miles on the clock as well.

Actually, you guys are a "little" wrong... There ARE in fact clutches in the G80 ... They are not like the older "limited slip" types like in the older F-Bodies or Trac-Lok JEEPS ...

There are 3 (I think) on the outboard side of the carrier that compress when a difference in speed between axles is noticed... When the Delta P reaches 200 rpm, then the clutches lock together, simultaneously, a fly weight so to speak swings out under centrifugal force, and this activates FULL lock...

Actually, here's what EATON Says happens with the parts:

The differential is set up with a flyweight governor that responds to differences in wheel speeds, and disc packs that are mounted between the side gear and the case.

Whenever one wheel is spinning substantially faster than the other, the governor spins rapidly, causing the flyweight to open. That flyweight then catches on a latching bracket and the lockup process begins.

During lockup, a self-energized clutch system causes a cam plate to ramp against a side gear. This ramping action compresses those disc packs mentioned earlier. The ramping continues until both axles - and therefore both wheels - are spinning at the same speed. This is full lock, and it prevents any further wheel slip. (Note: Axle lockup can only occur at speeds below 20 mph.)

The entire lockup process takes about a split second, and is virtually unnoticeable by the average driver. When both wheels regain traction, unlocking occurs and things go back to normal.

The clutches have a limited effect on traction, and basically just get/keep the other side of the carrier in rotation to keep the diff from slamming together when the 200 rpm Delta P is reached...

I will say, these clutches are pretty durable, and don't wear like the old type do...

One thing I don't like about this design, is that the system needs to see one side spin 200 rpm faster than the other to acheive full lock... In off road situations one might need to ease into the power to negotiate an obstacle rather than goose it a little to allow full lock ... Plus, while the diff is waiting to find full lock, the loose wheel is digging you deeper ... The system works great if you are carrying tires, but if you are just on all fours in loose stuff, it has it's disadvantages ... :)

I stand corrected!!
As I said to Steel. I hadn't seen a diag of the G8O
as was trying to reference to the Posi type plates

I went to the www.Eatonautomotive.com site which does show a working breakdown

I've monitor my diffs frequently [now over 15K] and have had no problem with leaks or lockup by full filling