Differential Clunking

by Dave Barnestable
(Tidewater VA)

I have a 2007 auto C6. I'm getting a clunk from the differential when I decelerate then accelerate at low speed (15 to 30 mph or so). It is particularly evident around turns. The differential fluid was just replaced at the dealership. Is this a possible u-joint or bushing issue? I also get a clunk shifting into reverse or drive when the car is cold.

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Mar 21, 2011
Gear Lube Additive GM TSB #07-04-20-002
by: Corvette web central

Rear Axle Clunk and/or Chatter Type Noise on Turns (Drain/Refill Rear Differential Fluid and Add Specified Limited-Slip Axle Additive) Number: #07-04-20-002 Date:(04/16/2007)Models: 2004-2007 Cadillac XLR (Including V-Series and Export) 2005-2007 Chevrolet Corvette (Including Z06 and Export)ConditionSome 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. Add the increased amount of limited-slip axle additive specified below. 89021677 (89021678 In Canada)
Synthetic Axle Lubricant
Quantity: 2
(3 for Z06 and Export)

1052358 (992694 In Canada)
Limited-Slip Axle Additive
Quantity: 2

Mar 18, 2011
by: Corvette-web-central

Corvettes don't have any U joints on the C6's. The problem sounds like the rear end. I would take it back to whoever changed the fluid and have them double check the service and fluid type. Its important that the fluid be approved for limited slip differentials. Most synthetic fluids are approved for this type of differential. Some older versions of the fluid did not have this rating. They required an additional additive called friction modifier. I would check these two items out first.

If after that you see no change a good inspection would be recommend of the drivetrain. Special attention to the differential, CV joints and Rear Wheel Bearings.
Please let US know what you find out!

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