The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Beam shake vibration is usually felt in the seat and occurring at speeds between 40-50 mph (64 - 80 km/h). Hertz readings using an EVA tool are normally between 8-24 Hz. This condition is most common on extended cab and crew cab models but has also been noted in other models.
The severity of beam shake may vary from vehicle to vehicle. To determine if the concern is beam shake, please perform the following:
Test drive vehicle to confirm the condition. A beam shake condition will usually respond to concrete type pavements more than asphalt, so the vehicle should be driven over both surfaces if possible.
Place 200-500 pounds in the pickup bed between the closed tailgate and the wheel wells. A beaming condition should dissipate.
Note: Tires with excessive Radial Force Variation (RFV) or out-of-roundness can intensify the frame beaming concern. The following radial force variation numbers should be used as a guide:
P-Metric tires (2WD 1500)
12 lbs or less
P-Metric tires (all others)
24 lbs or less
30 lbs or less
If the concern is determined to be beam shake, this is a characteristic of the vehicle and currently no repair attempts should be made. With your help in the use of the Field Product Reporting process GM Engineering is currently developing an enhancement to the body mounts to reduce this concern on the 1500 Models. On going testing has pushed the timing of these mounts to the first half of 2007. There will be no enhancement made to the 2500 and 3500 models. At this point no more Field Product Reports are needed and thanks for your help.
Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.