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Gary
Gary, ASE Certified Technician
Category: GMC
Satisfied Customers: 15704
Experience:  GCM master tech over 25 years
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I purchased a 2008 yukon xl denali awd with 105,000. I have

Customer Question

I purchased a 2008 yukon xl denali awd with 105,000. I have noticed that when I accelerate hard from coasting there is a thump or lurch. This occasionally happens on deceleration as well. I plan on getting a transmission flush at the dealership. Any thoughts?
Submitted: 1 year ago.
Category: GMC
Customer: replied 1 year ago.
Any thing I can check for slop in the driveline?
Expert:  Gary replied 1 year ago.

I am sorry for the long wait

4X4 ?

did this problem start out of the blue one day ?

how long have you owned this truck ?

Customer: replied 1 year ago.
AWD, just purchased about a week ago. Didn't notice during test drives bc I was being gentle with the wife in the car. With smooth acceleration it seems to shift smooth. It happens primarily when you get on the gas hard after coasting a little.
Expert:  Gary replied 1 year ago.

ok

these AWD and 4WD trucks all have a somewhat of a drive line clunk when letting off and coasting then getting back into the gas as these drive line systems by design when you add up the back lash so to say between the transmission and transfer case and rear axle this can be a normal noise heard

but it is best to be sure that there is nothing wrong with the drive line system

we did have some with too much rear axle backlash causing excessive clunking like this and a few rare ones with excessive transfer case back lash also

it is best to have the drive line inspected for the correct back lash first and correct anything that the bask lash is over spec...usually like the rear axle is @ .010 of back lash which any shop can inspect and check with a dial indicator and also the u-joints checked for any play in them

if the specs are normal tolerance or within specs then there is not much you can do to correct this issue

but again the drive line must be checked to be sure

if everything checks out good including the u-joints then this bulletin apply s for this type of issue

# *****: Information on Driveline Clunk Noise - (Nov 18, 2014)

Subject: Information on Driveline Clunk Noise Models: 2015 and Prior GM Passenger Cars and Light Duty Trucks

This Bulletin has been revised to add the 2015 Model Year and remove the Important statement. Please discard Corporate Bulletin Number 99-04-20-002H.

Some customers of vehicles equipped with automatic transmissions may comment that the vehicle exhibits a clunk noise when shifting between Park and Drive, Park and Reverse, or Drive and Reverse. Similarly, customers of vehicles equipped with automatic or manual transmissions may comment that the vehicle exhibits a clunk noise while driving when the accelerator is quickly depressed and then released. Tipping into the throttle after deceleration can also result in some level of clunk as the driveline is loaded in one direction (coast) then with throttle reapply the driveline gets loaded in the opposite direction (drive). On manual transmission vehicles depressing the clutch while in a deceleration immediately releases load on the driveline and may produce a clunk noise as the driveline unloads.

Note : Compare this complaint vehicle to a like vehicle. If the results are the same, this is a normal condition. For additional diagnostic information, refer to the appropriate Service information.

Whenever there are two or more gears interacting with one another, there must be a certain amount of clearance between those gears in order for the gears to operate properly. This clearance or freeplay (also known as lash) can translate into a clunk noise whenever the gear is loaded and unloaded quickly, or whenever the direction of rotation is reversed. The more gears you have in a system, the more freeplay the total system will have.

The clunk noise that owners sometimes hear may be the result of a buildup of freeplay (lash) between the components in the driveline. For example, the potential for a driveline clunk would be greater in a 4-wheel drive or all-wheel drive vehicle than a 2-wheel drive vehicle. This is because in addition to the freeplay from the rear axle gears, the u-joints , and the transmission (common to both vehicles), the 4-wheel drive transfer case gears (and their associated clearances) add additional freeplay to the driveline.

In service, dealers are discouraged from attempting to repair driveline clunk conditions for the following reasons:

^Comments of driveline clunk are almost never the result of one individual component with excessive lash, but rather the result of the added affect of freeplay (or lash) present in all of the driveline components.

Because all of the components in the driveline have a certain amount of lash by design, changing driveline components may not result in a satisfactory lash reduction.

^While some owners may find the clunk noise objectionable, this will not adversely affect durability or performance.

^For additional diagnostic information, refer to the appropriate Service Information.

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