K 2500 Truck 4WD V8-379 6.2L DSL VIN C FI (1989)
Vibration Damper: All Technical Service Bulletins
Brakes, Rear - Moan, Howl Noise Upon Light Acceleration
GMC NUMBER:
90-5-121
GROUP:
5 Brakes
DATE:
March, 1991
CORPORATE
NUMBER:
065023
SUBJECT:
REAR BRAKE NOISE/HOWL/MOAN
MODELS:
1988-90 C3 AND K3 LIGHT DUTY TRUCKS WITH SINGLE REAR WHEELS
Some owners of 1988-90 C3 and K3 light duty trucks may experience a moan or howl noise upon brake applications. The noise may be more noticeable
at low speeds nearing the end of the stop. The noise is caused by normal brake drum vibrations causing the rear brake backing plates to oscillate at their
resonant frequency. The noise will not damage any of the vehicle components. To correct this condition the rear axle assemblies on C3 and K3 trucks
have been modified to change the resonant frequency.
VEHICLES INVOLVED
Vehicles built after the following breakpoints have the new axles installed in assembly:
VIN
Plant
GMC Truck
1GTGK34N8LE548173
Pontiac East
Chevrolet
1GCGK34N6LE244095
Assembly
GMC Truck
2GTGK39N6L1561496
Oshawa Truck
Chevrolet
2GCGC39N6L1252916
Assembly
Vehicles from Fort Wayne Assembly are not affected by this change as Fort Wayne does not build the C3 or K3 series vehicles.
SERVICE PROCEDURE:
To correct this condition in service a tuned dampener assembly has been developed. When installed at the rear leaf spring "U" - Bolts the dampener will
oscillate 180 degrees out of phase with the resonant frequency effectively eliminating the generation of the noise.
