Knocking sounds when the wipers change direction may be caused by:

• A. Worn blade
• B. Worn splines on the wiper pivot
• C. Damaged motor mounting
• D. Loose linkage

Answer: (B)

When the wipers change direction, a sharp knock points to backlash in the drive interface, specifically wear at the splines that connect the wiper pivot to the drive train. The motor reverses and the next tooth on the spline must engage smoothly. If those splines are worn, there’s play in that connection, so the teeth take up the gap with a distinct snap as direction changes. A worn blade would cause streaking or poor contact across the glass, not a direction-change knock. Damaged motor mounting tends to produce vibration or noise all the time, not just at reversal. A loose linkage can cause a clunk, but the characteristic knock on reversal is most consistent with spline wear at the pivot. If you suspect this, check for visible or felt play at the wiper pivot and plan for replacement of the pivot or related drive components.