Axle Noise: Knock

WARNING: This page is about a different car, the 2005 Ford RV Cutaway, 2005 Ford Econoline, 2005 Ford E450 Super Duty, and 2005 Ford Cutaway. 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: Inspecting Differential Ring Gear And Pinion For Damaged Area

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: Inspecting Differential Ring Gear And Pinion For Damaged Area
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.