A vibration may be felt or a noise heard during hard acceleration on some 2015-2018 Colorado and Canyon models equipped with the 3.6L V6 engine (RPO LGZ) and 8L45 automatic transmission (RPO M5T).
When under acceleration at speeds of 48–52 mph (77–83 km/h), the driveline angles may become extreme during axle wind-up, resulting in a 2nd-order vibration. To adjust the angle, install a tapered shim between the axle and leaf spring.
Before installing the shim, check that the vehicle trim heights are within specification, there are no aftermarket modifications on the vehicle that may affect driveline working angles, and there are no signs of accident damage that may affect the position of the drive axle, axles, propeller shaft support bearing (if equipped) or the transmission or transfer case (if equipped).
In addition, inspect the condition of the leaf springs, mount bushings, mounting hardware, suspension structure, propeller shaft u-joints, and transmission mounts for any damage or excessive wear.
To install the shim, raise the vehicle and, using a hydraulic jack stand, support the rear axle. Apply tension to each end of the leaf spring using a C-clamp. (Fig. 12)
Fig. 12
Next, remove the lower shock absorber nut and remove the rear spring anchor plate. Lower the hydraulic jack stand slightly in order to slide the 2° shim under the spring and the bolt up through the hole in the spring. (Fig. 13)
Fig. 13
Remove the center bolt from the leaf spring pack. Install the tapered shim and the supplied bolt up through the spring. Torque the nut to 100 Nm (74 lb.-ft.) + 130°. Install the rear spring anchor plate.
TIP: The thicker side of the shim goes toward the front of the vehicle to bring the pinion nose down.
If the vibration is improved, test for any brake-induced shudder by applying moderate braking at 45 mph (72 km/h) and noting any vibration at approximately 28–30 mph (45–48 km/h). If there is objectionable brake-induced shudder, remove the 2° shim and install the 1° shim.
Refer to Bulletin #18-NA-356 for additional information and part numbers.
– Thanks to Charles Hensley
