I did the Amsoil fluid and additive change last fall. It didn't help, but it wasn't any worse. Now after spending the winter in the garage, my '05 is ten times worse than it was.

 

That's interesting because my 06 sat in the garage all winter and was totally quite when I took it out. The Amsoil works well in some cases while not in others? Wonder what the difference might be? I was concerned about not driving it for 5 months but it was the same as when I put it away for the winter. How many tubes of the modifier did you add when you did your change out? I used 2 tubes of the stuff because someone had recommended it. My posi unit still worked just fine because I.. errrr. checked it out several times.

 

Here is a copy if anybody would like to print out and take with them. We have done a ton of the procedures lately and it has taken care of all the issues related to it.



07-04-20-002A: Rear Axle Clunk and/or Chatter Type Noise on Turns (Drain/Refill Rear Differential Fluid) - (Jan 9, 2008)


Subject: Rear Axle Clunk and/or Chatter Type Noise on Turns (Drain/Refill Rear Differential Fluid)


Models: 2004-2008 Cadillac XLR (Including V-Series and Export)

2005-2008 Chevrolet Corvette (Including Z06 and Export)




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This bulletin is being revised to change the fluid recommendation and to remove the requirement of adding friction modifier. Please discard Corporate Bulletin Number 07-04-20-002 (Section 04 -- Driveline/Axle).


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Condition
Some customers may comment on a clunk and/or chatter type noise from the rear of the vehicle while making turns.

Cause
This condition may be caused by slip/stick of the posi-traction clutch plates due to insufficient limited-slip axle additive. As plates slip and stick, a jumping or jerking feel occurs accompanied by a clunk noise.

Correction
Important: DO NOT remove the differential cover from the rear or the two sides. It is not necessary to flush the old fluid from the differential.

Drain and refill the rear differential fluid using the procedure listed below.

Draining Procedure

Raise and support the vehicle.
Clean any dirt from around the differential drain plug.
If not equipped with a differential cooler, remove the drain plug (1) and washer (2) from the differential.



If equipped with a differential cooler:
4.1. Using a bent tip screwdriver, remove the quick connect fitting retaining ring (3) from the quick connect fitting (4) and discard the retaining ring.

4.2. Remove the differential cooler inlet pipe from the differential nut.

Drain the fluid.
Filling Procedure




If not equipped with a differential cooler, install the drain plug (1) and washer (2) to the differential.
Tighten
Tighten the differential drain plug to 35 N·m (26 lb ft).





If equipped with a differential cooler:
2.1. Install a new retaining ring.

2.2. Connect the differential cooler pump inlet pipe (2) to the differential. A distinct snap should be heard or felt when assembling the cooler pipe to the fitting.

2.3. To ensure the cooler line is properly installed, give the cooler pipe a gentle pull.

Clean any dirt from around the differential fill plug.
Remove the fill plug and washer from the differential.
Important: DO NOT add any limited-slip additive (friction modifier). With this new fluid (Dexron LS Gear Oil 75W-90) it is no longer required to add friction modifier. If friction modifier is added, it will cause the fluid to lose some of it's friction reducing properties as well as reducing seal life.

Fill the differential with the new DEXRON® LS gear oil, P/N 88862624 (Canadian P/N 88862625). Refer to the table listed below for lubrication specifications.
Check the fluid level to ensure it is even with the bottom of the fill plug hole to no lower than 6 mm (0.25 in) below the opening.
Install the fill plug and washer to the differential.
Tighten
Tighten the differential fill plug to 35 N·m (26 lb ft).

Important: Steps 8-13 are for vehicles equipped with the differential cooling system. For vehicles not equipped with the cooling system, proceed to step 14.

Raise the vehicle so the wheels are about a foot off the floor. Make sure the wheels can spin freely without obstruction from the hoist or any nearby items.
Start the vehicle and put the transmission in second gear. Slowly accelerate to 10 mph and hold this speed for one minute.
Turn the vehicle off .
Raise the vehicle.
Check the fluid level in the differential. Add fluid until the recommended level is reached.
Lower the vehicle.
Once the differential fluid has been changed, the vehicle must be driven in 8-10 tight figure eight maneuvers to heat the fluid and allow the fluid to be worked into the clutch plates.
Lubrication Specifications Application
Quantity

Metric
English

2004-2005 XLR (Including Export) and 2005 Corvette (Non Export)
1.72 liters
1.85 quarts

2006-2008 XLR (Including V-Series and Export) and 2006-2008 Corvette (Non Z06)(Non Export)
2.0 liters
2.11 quarts

2005 Corvette Export
1.88 liters
1.99 quarts

2006-2008 Corvette Export (Non Z06)
2.16 liters
2.28 quarts

2006-2008 Corvette Z06
2.75 liters
2.91 quarts

 

I did the double dose of modifier the second time around and that has held up for thousands of miles so far.

Glad to see at least GM has something newer to try at least if the double dose solution gives up the ghost.