How do Brake Calipers work

How do Brake Calipers Work

This guide captures ‘bygone’ advice on how break callipers work on a Classic Car. It is part of my series Classic Car Maintenance DIY Guides. However Classic Car Basic Service is also a great place to start and provides further information on brakes as does How To Change Brake Pads.

Useful information for Classic Car and Retro Car enthusiasts, as many of these tasks are no longer required on modern day cars.

Remember folks these are ‘bygone guides’ … useful but the safety and personal protective equipment measures are reflective of bygone awareness. Stay safe.

What are Disc Brakes

Disc brakes work like the caliper brakes on a push-bike. Yet with friction pads instead of blocks slowing the disc and so the wheel. When the pads become worn the cars braking will inevitably be affected and unless the pads are changed the discs themselves may be damaged.

How Do Brake Calipers Work

On most later Classic Cars disc brakes were fitted only to the front wheels, because the forces under which this type of brake operates tend to make the design of the handbrake mechan­ism fairly complicated. Yet earlier Classic Cars did not use disc brakes.

Many of the more expensive and higher performance cars have disc brakes all round.

Replacing the brake pads on disc brakes is a simple job (the second time you do it!).

The hardest part of the job is becoming familiar with the particular brake on which you are working. First you should identify which type of disc brake your car uses.

Disc Brake Basics

The design of disc brakes varies but the principle on which they work is always the same. At each disc-braked wheel a caliper unit straddles a cast-iron disc mounted on the wheel hub (or on inboard brakes on the axle near the differential housing).

Brake Caliper Basics
When pressure is applied via the foot brake and the system comes under pressure this thrusts out the disc pads against the rotating disc. The friction created will slow down the disc.

Different Types of Brake Caliper

Disc-brake calipers come in three main types:

Most modern cars have a fixed caliper, in which each pad is operated by its own piston while the caliper remains stationary.

Fixed Caliper Brakes
A fixed caliper system in which each pad is operated by its own piston. This
is the most common disc brake system

The sliding caliper has one cylinder, but two pistons. One piston acts directly on one of the pads. The other moves the yoke in the opposite direction and thus operates the second pad.

Sliding Caliper Brakes
The sliding caliper system has two pistons, one operates directly on one pad, the other on the yoke which slides along to force the second pad (the indirect pad) against the disc.

The swinging caliper has only one cylinder and piston, but is pivoted in the middle and designed so that one side moves in the opposite direction to the other. Unlike the others, it uses wedge-shaped brake pads.

Swinging Caliper Brakes
In the swinging calliper system, only one pad moves and one is fixed. The force from one pad is equalised by the whole caliper ‘swinging’ so that the pressure is equal on both sides.

Some recent dual-line braking systems (usually found on higher performance vehicles) have four-piston calipers. But the basic methods of changing the pads are the same, regardless of whether the caliper has one, two, three or four pistons.

Unlike drum brakes, disc brakes have no pull-off springs to retract the pistons after each use of the brakes. Instead, rubber seals in the caliper make the piston(s) retract. The seals also prevent the leakage of fluid past the pistons.

Disc brakes compensate automatically for brake pad wear, each piston allowing only a small running clearance between the pad(s) and the disc.

When to change Break Pads on a Classic Car

The condition of the pads should be checked at least every 10,000 km (6,000 miles).

Inboard pads such as those fitted to the Rover 2000 wear more quickly than normal disc pads and need to be checked more frequently.

The wedge-shaped pads found on swinging calipers should be changed when worn flat to 1.5 mm (1/16 inch).

Other pads should be changed when the lining thickness is down to 3 mm ( 1/8th inch)

Rear Disc Brake considerations

Some cars with rear disc brakes have handbrake pads which need to be adjusted manually (a need which is normally indicated by increased movement of the hand­brake lever)

Here again, regular inspection of the linings is necessary. The safe minimum thickness is 1.5 mm; wear beyond the recommended limits may damage the disc resulting in an expensive replacement having to be carried out.

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