Rear axle thump

[VTwinMan]

I have noticed that every once in awhile when I start to take off after being stopped at a light it feels like I have about a 1 second delay between when the engine starts revving and when the back tires start to turn. It feels like a small thump (like it's taking up slack in the drivetrain) and then it starts to go. It has done this in AWD and 2WD and I don't hear or feel any other noises or vibrations.

Has anybody else experienced a similar feeling?
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VTwinMan

[GMJosh]

I have the same issue but haven't asked the dealer about it. I also have a locking rear diff...

[VTwinMan]

Originally Posted by cmjdisanto

I have the same noise. I don't take much stock in what my dealership service department has said, so with that in mind they say it is because I have a locking differential. So I will go with that answer.

Did they say (or do you know) why that would make any difference?
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VTwinMan

[GMJosh]

Here's some info on how the locking diff works. I suppose the thump could occur when the flyweight catches on a latching bracket but it seems like a stretch since it shouldn't be locking in the cases we're discussing. The description is interesting so I figured I'd post it. You can get more info at http://www.traction.eaton.com/prod2.htm

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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.

[VTwinMan]

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.

Hmmm, this only seems to occur when I accelerate fairly rapidly. It has never occured when I accelerate very slowly. Could that create the torque needed to engage the other half of the axle?

[GMJosh]

I guess it's possible but it still seems like a long shot to me. Here's a link to another thread on a similar symptom. These guys describe more of a metal "clank" but it may help you to narrow the scope a little. My noise is more of a "thud" - as if the spare tire was swinging into the tailgate (but that doesn't seem to be the case).

http://www.automotiveforums.com/vbul...ht=drive+shaft