2000 Bravada question about changing locking rear axle oil

I have a 2000 Bravada that has the "hopping" problem during slow speed turns such as parking lots, etc. The transfer case fluid has been changed twice in 2.5 years, the last time being a year ago using the
recommended GM fluid. The hopping has gotten worse and a GM dealer told me since I have a locking differential that I should probably change the rear differential oil as well. The owners manual says to only use GM axle lubricant, PN.1052271. There is no description of what that lubricant is. They also give the same part number for the front axle lubricant which is a standard differential and call it "SAE 80W90 ". When I called the dealer they tell me that my book is wrong and that I need this special SAE 75W90 oil at about 29.00 a quart. Now if someone could please answer six questions for me /i would be extremely grateful: 1. What is the correct oil for this axle? 2. How much do I need for a complete drain and refill? 3. Is there a drain plug on these axles or is there a plate on the rear of the carrier that has to come off? 4. How likely is it that a rear differential oil change may cure my problem ? 5. If this is my problem what is actually happening in the differential to cause this? 6. How much damage typically occurs from driving a car with this type of symptom for any length of time and what will we notice? Thanks very much for any advice. Lenny Stein.
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Given that the fluid has been changed a couple of times already, I doubt one more change is going to fix the problem. My guess is that you have an internal mechanical problem.
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snipped-for-privacy@yahoo.com wrote in

some 'hop' on solid surface is considered normal with no repairs needed or possible. i dont find it pleasant but i do find it on all models with locking diff's (GM being the most bothersome).............you may end up throwing money at it till sold w/no results......i know i really didnt answer any of your ??? but if the owners manual aint right, how would you possibly trust any stranger here for better info?........kjun
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What 4x4 do you have, 1 speed or 2 speed. What position are you running the 4x4 in. Rear diff is a locker type, if you're not spinning, should be no limited slip action. Oil is 75w90, no friction modifier. In the auto position, there should be little to no binding. I suspect an internal problem in your transfer case.

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snipped-for-privacy@yahoo.com wrote:

Is your rear axle a true locker or a limited slip? If the latter it does require a special lubricant.
nate
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snipped-for-privacy@yahoo.com wrote:

Tell them to look up this bulletin
Shudder, Rocking Motion, Binding, Feels Like Vehicle is Stuck in 4WD (Crow Hop) When Turning at Low Speeds (Replace Transfer Case Encoder Sensor and Reprogram TCCM) #02-04-21-008A - (02/13/2003
This is what you need done to fix your problem. Of course, perhaps this bulletin has already been performed...so you need to check on that first. Even if it has, the encoder sensors are troublesome anyway. It may need another one, and I've even seen some that need the whole encoder motor replaced.
Ian
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snipped-for-privacy@yahoo.com wrote:

I would use Royal Purple 75W-90 Synthetic which includes limited slip additive already in the fluid. It goes for around $10/quart at our local NAPA Auto Parts.
John
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It doesn't require a limited slip additive, it's a locking type.
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