Brake specialist APEC has highlighted its advice on how to prevent one of the most common faults with braking systems, brake judder. 

The dreaded judder occurs when customers describe pulsing through the brake pedal or shaking through the steering wheel, when they brake. The cause is almost always that the brakes are suffering from Disc Thickness Variation (DTV). This means the outside and inside disc surfaces are no longer parallel, so the pads are pushed into the thinner areas and kicked back out by the thicker areas. This violent movement is transmitted back through the caliper pistons and brake fluid to the pedal.

Judder can be caused by a number of issues, such as poor quality disc manufacture, incorrect fitting, sticking calipers and bad driving habits.
Buying disc from reputable brands such as Apec will mean quality is not an issue. However, even quality discs fitted wrongly can judder. Cleaning the hub before fitting a new disc is essential. Even the tiniest spec of dirt or rust causes an inboard-outboard movement that increases towards the outer edge of the disc. This will get worse with repeated applications and lead to judder.

A less common, but still significant, cause of judder is sticking calipers. If the caliper slide pin or guidepost pin is rusted, dirty or bent, the caliper won’t ease back from the disc when the brake pedal is released, causing the pads to rub against the disc. This leads to an uneven build-up of pad material and hot spots on the disc, both resulting in judder.

Failure to bed in new pads can also be a major source of judder. Braking hard before a protective layer has built-up means the transfer of material will be patchy and uneven, again leading to the dreaded DTV. More gentle braking is recommended for the first few hundred miles so that an even layer of pad material can be transferred to the discs, providing a consistently smooth surface that means the whole pad will contact the disc on each application, without creating high spots on the pad or variations in disc thickness. Heavy use of brakes too early in the pads life is therefore to be avoided.

Apec says its pads make bedding-in easier because the High Pressure Treatment process used during their manufacture reduces the time required for bedding-in. However, it’s still necessary to treat the brakes gently for the first few hundred miles.