Suspension Vibration Or Frame Beaming At 40-60 MPH (64-80KM/H) - keywords front rear shake shock spring tire

This PI was superseded to add additional info about an oily film on the new mounts. Please discard PIT3009H.

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:

1. 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.
2. 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

LT-tires 30 lbs or less

If the concern is determined to be beam shake, this is a characteristic of the vehicle. GM Engineering has released updated body mounts to reduce this concern for the Crew and Extended Cab Models. There will be no changes made to the Regular Cab Models.

FOR CREW AND EXTENDED CAB MODELS, REPLACE THE REAR CAB MOUNTS WITH UPDATED PARTS LISTED BELOW. THESE PARTS SHOULD NOT BE USED ON REGULAR CAB MODELS.

New upper and lower mounts should be installed at the left and right rear cab position. The new LOWER mount is a two piece design, meaning there is a rubber mount with a metal washer. Some models may use a one piece lower mount, meaning the rubber mount has a metal washer molded into it. If the vehicle has the one piece lower mount design, washers (PN 15854745, Qty 2) will be needed to be used with the new lower mount.

Note: Some new body mounts may have an oily film covering them. This oily film may be left on the mounts during the assembly process and does not indicate a faulty mount. Do not replace the mount for this issue.

Upper Mount 25791031 Qty 2

Lower Mount 25791032 Qty 2

Washer 15854745 Qty 2 (if needed)

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.