Drum brake lining

Brake lining is the friction material fitted to the brake shoes of drum brakes. When the service brake is applied, the brake camshaft presses the brake shoes against the inside of the brake drum, creating the friction required to slow the vehicle down. This system is mainly found on the axles of heavily loaded trucks, buses and off-road vehicles, where the enclosed design of drum brakes provides protection against water, sand and mud. For a safe and long-lasting repair, brake linings must always be identified using the vehicle chassis number. Visual comparison or selection based solely on the model name is never sufficient.

Brake linings for MAN F90, F2000, M2000, TGA, TGS, TGX and TG3, as well as for Mercedes SK, Axor, Atego, Arocs, Actros and Econic, differ according to axle type, drum diameter, brake shoe width, camshaft design and permitted axle load. For MAN Lion’s City, Lion’s Coach and Neoplan coaches, as well as Mercedes Citaro, Intouro and Tourismo, specifications also depend on the selected axles and brake configuration.

The correct Brake lining is selected based on, among other factors, length, width, thickness, rivet pattern, radius matching the brake drum and brake shoe type. The lining must fit the curved backing plate exactly; an incorrect radius causes a limited contact area, local overheating and uneven wear. Modern friction materials are asbestos-free and generally consist of fibre-reinforced composites with binders, mineral fillers and friction modifiers. The selected friction grade determines the coefficient of friction, temperature resistance, wear resistance and fade resistance. Softer grades are suitable for lighter-duty use, while harder linings are better suited to high axle loads, mountain routes, construction transport or intensive urban bus operation.

A wear inspection is not limited to the remaining lining thickness. Measure at several points using a vernier caliper or lining thickness gauge and compare the value with the manufacturer's minimum specification. Check both brake shoes on each wheel for even thickness, cracks, loose segments, glazing, burnt areas and contamination by grease, hydraulic oil or transmission oil. Oil-soaked brake lining has a severely reduced friction value and must always be replaced; cleaning does not provide a reliable solution.

Angled wear or linings worn on one side often indicate a sticking brake camshaft, worn camshaft bushes, a defective brake adjuster, broken return springs or an oval-worn brake drum. Remove the drum and measure the internal diameter with a drum gauge or internal micrometer at different angles and depths. Exceeding the maximum machining diameter, taper or ovality prevents a correct contact pattern. Then check the radial play of the brake camshaft, the free stroke of the brake cylinder and the operation of the automatic brake adjuster. In pneumatic systems, leaks, insufficient system pressure and a defective control valve must also be ruled out.

Always replace brake linings per axle, meaning on both the left and right side of the same axle, and use linings with an identical friction grade. For riveted versions, the rivets must have the correct diameter, head shape and clamping length. A rivet set too deeply damages the friction material; an insufficiently countersunk head can score the brake drum. Before installation, inspect the brake shoes for corrosion, deformation and damaged rivet holes. Also replace worn springs, bushes or a stiff brake camshaft to prevent recurring wear.

After installation, the brake shoes must be correctly adjusted via the brake adjuster and the brakes must be checked for equal braking performance. Carry out a test drive with controlled bedding-in cycles and avoid prolonged heavy braking during the initial load phase. Timely replacement of brake linings protects brake drums, brake camshafts and wheel bearings against heat stress. Thanks to technical support and a wide availability of brake parts, Braem helps minimise downtime for professional vehicles.