Handbrake is key to safe parking

The main purpose of a handbrake is to keep a parked vehicle from rolling.

The main purpose of a handbrake is to keep a parked vehicle from rolling.

But it has another job - to provide emergency braking if the hydraulically operated foot brakes should fail completely.

So by law it has to be fully mechanical, operated by steel cables bypassing the hydraulic system entirely and, with very few exceptions, handbrakes operate on the rear wheels only.

Normally a cable runs from the lever next to the driver to an equaliser link somewhere near the rear wheels. From there two cables are taken, one to each rear wheel, the equaliser ensuring that the two cables have equal tensions.

It is not so easy to incorporate handbrakes into disc brakes - this was one of the reasons why many cars retained drums at the rear long after changing to discs in front. But as the advantages of discs became irresistible, ways were found of doing so.

Two main designs are used.

In the first, a small brake drum is integrated into the rear disc brake rotor. It fits over a set of brake shoes, mounted on the backplate and operated by cable only - a purely mechanical mini drum brake. The other design uses a lever that turns a screw or twists a cam which presses the piston inside the disc brake calliper inwards, thus forcing the brake pads into contact with the disc and holding them there.

When it comes to adjusting a handbrake, the correct procedure is always to slacken off the cable adjuster until the cable is really slack. Then adjust the friction surfaces on the rear brakes to have a very small gap between them, and then adjust the cable so that the handbrake is holding the vehicle stationary on a slope when the lever next to the driver is pulled up four or five clicks, yet is not binding when the lever is fully released.

Do not try to adjust a slack handbrake on the cable adjuster only.

The problem doesn't lie in the cable. Adjustment is needed far less frequently on newer cars, but the procedure remains the same.

Apart from adjustment, the biggest potential problem with a handbrake is that the cables can rust and eventually seize up inside their sheaths.

This happens more readily if the handbrake is used rarely.