Axle Noise: Knock

WARNING: This page is about a different car, the 2006 Mercury Grand Marquis and 2006 Ford Crown Victoria. However, it is still accessible from the selected car via links, so may be relevant.

Knock, which can occur on all driving phases, has several causes including damaged teeth or gearset.

Fig 1: Identifying Damaged Teeth

Courtesy of FORD MOTOR CO.

In most cases, one of the following conditions will occur:

A gear tooth damaged on the drive side is a common cause of the knock. This can usually be corrected by grinding the damaged area.

Fig 2: Identifying Ring Gear And Pinion Damaged Teeth
Courtesy of FORD MOTOR CO.

NOTE: Measure the end play with a Dial Indicator Gauge with Holding Fixture, not by feel.

Knock is also caused by excessive end play in the axle shafts. Up to 0.762 mm (0.030 inch) is allowed in semi-float axles. The frequency of the knock will be less because the axle shaft speed is slower than the driveshaft.