Owners of some 1996-2007 light duty trucks and utilities equipped with four wheel drive (4WD) may comment about a groan, growl, or moan coming from the vehicle when operating the vehicle in 4WD.
The vibration that is heard or felt is a result of the front axle being excited to resonance at its natural frequency. This is a combination of the transfer case chain link frequency, engine firing frequency, tire circumference variation, and various other tolerances built into the 4WD system.
A groan, growl or moan noise on deceleration while in 4WD is also the result of loading the transfer case chain, which is a normal operating characteristic. This is an example of a transfer case link frequency noted above.
On certain models, such as 3/4 and 1 ton vehicle, tire pressures can vary from front to rear, based on the manufacturer's specifications.
Example:Â the manufacturer's specifications for tire pressures on a 2003 K2500 Suburban are front: 50 PSI, rear: 80 PSI.
The difference in tire pressures affects the rolling tire circumference from front to rear, which can increase driveline noise while in 4WD. This is a normal operating characteristic.
For test purposes, drop the tire pressure in the rear to match the front. If the noise is reduced or eliminated, this confirms the difference in tire pressures from front to rear can affect the noise when operated in 4WD. Set the rear tire pressure back to the manufacturer's specification.
For vehicles with same tire pressures front to rear, swap tires from an identically built vehicle that does not seem to exhibit the concern and re-evaluate both vehicles.
No repairs are recommended for this condition.
For more information regarding driveline noises while in 4WD, refer to the latest version of bulletin 01-04-18-001D.
- Thanks to Rusty Sampsel
The vibration that is heard or felt is a result of the front axle being excited to resonance at its natural frequency. This is a combination of the transfer case chain link frequency, engine firing frequency, tire circumference variation, and various other tolerances built into the 4WD system.
A groan, growl or moan noise on deceleration while in 4WD is also the result of loading the transfer case chain, which is a normal operating characteristic. This is an example of a transfer case link frequency noted above.
On certain models, such as 3/4 and 1 ton vehicle, tire pressures can vary from front to rear, based on the manufacturer's specifications.
Example:Â the manufacturer's specifications for tire pressures on a 2003 K2500 Suburban are front: 50 PSI, rear: 80 PSI.
The difference in tire pressures affects the rolling tire circumference from front to rear, which can increase driveline noise while in 4WD. This is a normal operating characteristic.
For test purposes, drop the tire pressure in the rear to match the front. If the noise is reduced or eliminated, this confirms the difference in tire pressures from front to rear can affect the noise when operated in 4WD. Set the rear tire pressure back to the manufacturer's specification.
For vehicles with same tire pressures front to rear, swap tires from an identically built vehicle that does not seem to exhibit the concern and re-evaluate both vehicles.
No repairs are recommended for this condition.
For more information regarding driveline noises while in 4WD, refer to the latest version of bulletin 01-04-18-001D.
- Thanks to Rusty Sampsel
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