Maximising the service life of bus brake calipers

Friction Braking - Bus & Coach Parts - Imperial Engineering

Reducing whole life costs and prolonging the service life of OEM disc brakes, or as they’re more commonly known, calipers, is a key issue for PSV operators in today’s climate of increasing cost pressures due to declining subsidies.

Produced by manufacturers including Knorr-Bremse, Wabco and Meritor, quality OEM calipers are designed to last the lifetime of a vehicle, providing they are routinely inspected and serviced.  Caliper failure typically occurs due to problems that could be identified and remedied during routine maintenance inspections.  Based on our own experience, we have identified four specific caliper-related faults that can be rectified upon inspection to ensure they deliver their intended service life:

Poor seal between caliper and actuator

This typically occurs after changing a spring brake when the unit has not been correctly refitted, preventing a seal to be formed.  Water ingress then takes place, leading to corrosion and eventually seizure of the caliper.

Missing sealing caps

Sealing caps, also known as ‘witches’ hats’ or adjuster caps, are intended to provide a seal for the caliper to prevent water ingress during service, or when a vehicle is being power washed.  As well as causing water-related damage, it’s also important to note that missing sealing caps will also result in MOT failure.

Torn caliper boots

Often caused by heat damage or road debris, tears and splits in a caliper’s protective ‘boot’ can be easily overlooked.  Over time, a damaged caliper boot will lead to dirt build-up and water ingress in the disc brake’s internal mechanism causing premature failure.  Fitting a replacement boot, which costs around £50, is an effective solution to this problem.

Seized caliper bearings

Dirt and water ingress due to damaged or missing seals can also cause the caliper’s bearings to seize.  This results in thermal overloading and component failure.

It is also important to ensure that running clearances are reset to their OEM specification whenever brake discs or pads are changed to ensure caliper service life.  A range of brake service tool kits and diagnostic equipment is also available to support maintenance, as well as specialist training on braking system inspection for technicians, which as a distributor Imperial Engineering provides to operators in conjunction with our OEM braking suppliers.  Some manufacturers have also introduced OEM remanufactured caliper programmes for the PSV market.

For further information call 01992 634255 or email