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Information On Driveline Clunk Noise (99-04-20-002O)
Reference number: 99-04-20-002O
Supersedes refnos: 56-44-01, 56-44-01A, 99-04-20-002, 99-04-20-002A, 99-04-20-002B, 99-04-20-002C, 99-04-20-002D, 99-04-20-002E, 99-04-20-002F, 99-04-20-002G, 99-04-20-002H, 99-04-20-002I, 99-04-20-002J, 99-04-20-002K, 99-04-20-002L, 99-04-20-002M, 99-04-20-002N
INFORMATION ON DRIVELINE CLUNK NOISE
TECHNICAL SERVICE BULLETIN
| Affected Model(s): | 2025 and Prior GM Passenger Cars and Light/Medium Trucks |
| Attention: | This bulletin also applies to any of the above models that may be from North America, Argentina, Brazil, Bolivia, Chile, Colombia, Ecuador, Paraguay, Peru, Uruguay, Venezuela, Europe, Kazakhstan, Uzbekistan, Middle East, Israel, Other Central America, Japan, Cadillac Korea (South Korea), GM Korea Company, China, Taiwan, Thailand, Singapore, Philippines, Australia/New Zealand, Caribbean, Egypt, Other Africa, South Africa |
| Supercedes: | This bulletin has been revised to add the 2024-2025 Model Years and additional Regions/Countries. Please discard Corporate Bulletin Number 99-04-20-002N. |
SERVICE INFORMATION
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.
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 universal 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 effect 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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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.