- Not an original spare part - Protects the surge brake's sliding rail from dust, dirt, and moisture A coupling dust cap for a surge brake protects the brake's sliding rod from dust, dirt, and moisture. During braking, the sliding rod moves inward as the trailer pushes against it, activating the brakes. The sliding rod is made of steel and lubricated to ensure smooth operation. The dust cap prevents contaminants from reaching the grease, allowing the sliding rod to function properly. Since the dust cap is exposed to all weather conditions, it should be replaced in a timely manner to maintain optimal protection for the surge brake. Replacing the dust cap: When replacing, note the type and/or brand of the surge brake (marked on the label of the brake unit), as this determines the correct dust cap size. Alternatively, measure the diameter on the coupling side and the diameter on the surge brake side. Take note of cutouts for mounting bolts, such as those used for ball couplings. Use a 19mm wrench to remove the bolts/nuts on the coupling and take off the old dust cap. Install the new dust cap and secure it with a cable tie if necessary. Reattach the coupling and tighten the bolts/nuts using a 19mm wrench or socket.