This article supersedes TSB 21-2253 to update the vehicle lines affected. Some 2021 F-150 (non-Raptor/non-Tremor) vehicles with rear gross axle weight rating (GAWR) of 1542 kg (3,400 lb) or 1724 kg (3,800 lb) shown on the vehicle certification (VC) label may experience a pop/clunk/snap noise from the rear of vehicle when driving up/down an incline at an angle (frame twist). This approach angle would be similar to entering or leaving a driveway. This may be due to movement between the rear spring and the rear spring mounting plate on the rear axle. To correct the condition, follow the Service Procedure to apply lubrication between the rear spring and the rear spring mounting plate mating surfaces on the rear axle.
