Driving a vehicle you’re unaware of the state of your brake calipers — road vehicles are not like aeroplanes and fitted with numerous on board monitoring systems – you may have a brake caliper ‘about to fail’ and you wouldn’t know it. What is failure in braking terms? A brake caliper must respond instantly to hydrauiic pressure and force the pads against the disc. The force involves can exceed 6000lbs per square inch – enough to crush bones.
OK – so you press the pedal and the car slows as expected. But whilst there is pressure forcing the pads against the disc there is no force pushing the pads off the disc. Release of the disc is passive and relies on caliper ‘recoil’. Recoil is will occur when hydraulic pressure is released and the caliper ‘sits back’ off the disc. This passive process is heavily reliant on effective lubrication of the caliper pin. If the caliper pin lubricant has dried out then the caliper will continue to grip the disc. Heat will transfer from the fast rotating disc rubbing against the pad to the caliper pin further drying out the grease until it is becomes completely ineffective.
Petroleum based lubricants – copper grease – will dry out fast. Red rubber grease has a mineral oil base and will also dry out. Eventually the caliper will move only when the pedal is pressed for sufficient duration and with sufficient force until finally it doesn’t move at all. Seized. At this stage the car will pull to the opposite side to the seizure on braking. Think how many people are told at the MOT they have a seized caliper ..’oh really ? how much is a new one?’
Key to preventing seizure is making sure the pads are not corroded in the clips/shims – use a dry lubricant like ProSlip CLIP. If the pads are corroded in the clips braking pressure is wasted in overcoming the resistance offered by the corroded ends of the pads in the clips……