Braking systems in commercial vehicles convert kinetic energy into heat. Under normal operating conditions, brake discs, drums and friction materials are designed to absorb and dissipate this thermal load.
Problems arise when heat is generated faster than the braking system can release it. Long descents, repeated heavy braking, high vehicle mass and demanding stop-and-go operation can push components beyond their intended temperature range.
The result can be brake fade: a temporary reduction in braking effectiveness caused by excessive thermal load.
What is brake fade?
Brake fade describes a reduction in braking performance as brake temperatures increase.
Friction materials are designed to operate within a defined temperature range. When this range is exceeded, their friction characteristics can change and greater braking effort may be required to achieve the same deceleration.
Brake fade should therefore be distinguished from permanent mechanical failure. Performance may improve again after the system cools, but repeated overheating can cause lasting damage to pads, discs, drums and surrounding components.
What causes excessive brake temperatures?
One of the most demanding situations for commercial vehicle brakes is a long descent with a heavily loaded vehicle.
Continuous use of the service brake generates large amounts of heat. If the driver relies primarily on the wheel brakes instead of available auxiliary braking systems such as an engine brake or retarder, temperatures can continue to rise.
Dragging brakes can produce similar thermal stress. A sticking caliper, incorrectly adjusted brake mechanism or other fault may keep friction components in contact even when the service brake is not being applied.
Signs of thermal overload
Workshops may find discoloration, glazing, heat marks, surface cracking or unusual wear on thermally stressed brake components.
Drivers may report reduced braking effectiveness, changes in pedal response or braking behaviour that deteriorates during prolonged use.
These observations should be evaluated together. Remaining disc or drum thickness alone does not necessarily indicate whether a component has been subjected to excessive heat.
Brake pads, discs and thermal compatibility
Correct dimensions are only one aspect of brake component selection. Friction material, disc design and the intended vehicle application also influence thermal behaviour.
A brake pad must provide suitable friction characteristics across the expected operating-temperature range, while the disc or drum must tolerate repeated heating and cooling cycles.
Replacement components should therefore be matched to the relevant brake system, axle and vehicle application rather than selected only by approximate dimensions.
Diagnosing an overheating brake
If overheating is concentrated at one wheel or axle, the underlying cause should be investigated before replacing friction components.
The inspection may include caliper movement, brake adjustment, actuator operation, pad or shoe condition and evidence of uneven contact. Comparing the condition of components across the axle can also help identify abnormal behaviour.
Replacing an overheated disc or pad without correcting a dragging brake can result in the same damage occurring again.
Reducing the risk of brake fade
Brake fade prevention begins with a correctly functioning braking system and suitable components, but vehicle operation also matters.
On long gradients, auxiliary braking systems can reduce the thermal load placed on the service brakes. Appropriate gear selection and braking technique are particularly important for heavily loaded vehicles.
Regular inspection can identify uneven wear, dragging brakes and previous signs of overheating before they develop into more serious problems.
Conclusion
Brake fade occurs when thermal load exceeds the operating range of the braking system and friction performance begins to decrease.
Long descents, repeated heavy braking and dragging components are common contributors. Workshops should therefore consider both component condition and the cause of excessive heat when investigating brake-related problems.
Correct diagnostics, suitable brake components and appropriate use of auxiliary braking systems help maintain consistent braking performance under demanding operating conditions.
FalkePro – Commercial Vehicle Spare Parts
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