When are the ball joint and tow ball coupling worn out?

Ball head on the towing vehicle: The new ball head has a diameter of 50 mm; the wear limit is 49 mm. Measure in several directions using a calliper — the ball wears down in an oval shape, and even a single point measuring less than 49 mm means it needs replacing.

Tow ball coupling on the trailer: Signs include noticeable play on the ball, rattling whilst driving, or a coupling that no longer engages properly. Many couplings have a wear indicator on the handle — if the pointer is in the red zone, it needs replacing.

Assess both together: a new coupling fitted to a worn-out ball will continue to rattle.

Lubrication: The ball and coupling wear out much faster if left dry. An important exception is anti-sway couplings: their friction linings must remain grease-free; in this case, only the ball is cleaned. Grease on the linings renders the anti-sway damping ineffective and ruins the linings.

A worn-out pair will be flagged during the annual general inspection. Replacement: Ball couplings and accessories.