Mechanics

Z71 4X4 'CLUNK' NOISE

1999 GMC Sierra

Transmission problem
1999 GMC Sierra V8 Four Wheel Drive Automatic 100000 miles

Having trouble to identify a clunk in this truck. Truck when stopped and starting up again on pavement feels like slight feeling of tire spin on gravel and then a clunk. Does not do it every time. Also notice the clunk on 2 nd to 3 rd shifts. Many times the shift is smooth and quiet. Even when the truck makes the 'clunk', the shfit is smoot, not jerky. Have new u-joints and cleaned the yoke to ensure it was not sticking. Does not seem to matter if the truck is loaded down (pull trailer) or empty. Can not see anything underneath that shows sign of movement or slippage.
Any thoughts on what I should inspect?
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Toronado85
June 1, 2008.




A couple of questions first.
When was the last time the tranny was serviced?
Has the transfer case fluid been changed recently?
Does this make the same clunking noise when you're in four wheel drive?
If memory serves, this model's transfer case is a chain drive type. If the chain has stretched (or is damaged), it could cause the clunk/gravel spin.
Check the slip joint on the rear drive-shaft (might be starting to strip).
Check the tranny mounts (cross-member and tranny to cross-member bolts).
My only other guess is the tranny is starting to have " issues".
Good Luck

Tiny
Danimalgmc
Jun 23, 2008.
Tranny serviced, oil and filter by GM dealer recently (20k). Transfer case oil changed at same time.

Noise is not nioticeable in 4x4 operation.

New u-joints last year (and regreased this spring)

Tranny mount checked and solid.

I did change rear diff oil and add GM addative, and 50% of niose is gone. Rear end was good, took back off, no metal filings, clean and new gasket added. Changed front diff oil at same time.

Added GM replacement kit rubbers to the leaf springs (kit) and noise is gone. GM said these sometimes when worn permit 'slip' in the springs and that is the noise. Been only two days now driving, noise is 99% gone, just normal from what I can tell.

Anyone else every have a similar experience?
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Tiny
Toronado85
Jun 24, 2008.

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