Axle Noise: Knock

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

Fig 1: Identifying Knock

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: Locating Gear Tooth Damaged
Courtesy of FORD MOTOR CO.

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

Knock is also caused by excessive in-out 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.