Assessment of damage to drum brake linings

Service information should be the basis for evaluating drum brake linings.

Scope of application

It is up to the inspector to assess whether the lining needs to be replaced. His decision must take into account - in addition to the visual characteristics - also the overall impression of the vehicle and its use. If the causes of the faults described here are not remedied, further deterioration is to be expected. Linings should be tested at regular intervals. Warranty rights depend on the specific case and specific boundary conditions.

Jags

Chips on the edges in a certain area, as shown in Fig. 1, are a sign of normal wear (and therefore not a product defect) that does not yet require replacement. Keep in mind that:

• Fresh nicks on the edge of the outer side of the lining are caused by incorrect disassembly of the brake drum. Chips on the circumference of the entire edge up to 8 mm wide over the entire thickness of the cladding are acceptable (fig. 1). Surface cracks up to a maximum of 15% of the entire surface of the cladding are independent of the position and permissible up to a depth of approx. 1.5 mm (fig. 1).
• Chips in the area of the base of the rivet are not allowed. The base of the rivet is the contact surface with the brake shoe.

Cracks on the friction surface

Cracks on the friction surface are a sign of normal wear. Cracks in the shape of a network, branches, are not critical. Replacement is only necessary when:

• The cracks will extend to the base area of the rivet
• One crack is longer than approx. 90 mm with a width of approx. 1 mm.

Thermal damage to the linings

Brake pads must be replaced after thermal overload. If the cause of thermal damage is not eliminated, e.g. by reducing the thermal load by adjusting the tractor accordingly, recurrence of such damage is to be expected. Typical signs of thermal damage include:

1. Ash on the surface and near the shore.
2. High porosity and brittleness of the cladding.
3. A major discovery of lining fibers.

Contact plane

If the contact surface in the lapped condition is less than 80%, the linings should be turned over. The plane of contact on one axis should be comparable.

Other remarks

In addition, the brake linings should be visually checked for the following features:

1. Oil or grease on the pads.
2. Heavy soiling on the linings.
3. Deep grooves on the surface.
4. The wear of the linings is not flat-parallel.
5. Blurred surface.