Brake Pad Wear checking is a most useful tool, not just to show when to change the pads, but to pick indicators of problems throughout the vehicles braking system.
During the braking process the friction material and brake rotor absorb large amounts of heat. The friction material also acts as an insulating barrier to slow the heat transfer to the brake caliper and other components. As the pad wears there is less friction material so more of the heat is transferred to other components. It is recommended that the brake pads be replace when there is less than 3mm of friction material remaining.
Note the position of each pad as you take them out of the brake caliper, also note any broken spring clips or shims that come out. Measure each pad at several positions along its length. In many cases the jaw of your measuring caliper can reach right across the width of the pad.
Pads that wear unevenly can show a taper when measured. In extreme cases this can be seen during the measurement process. Check the variation in thickness along the length of the pad and across the width of the pad. There is normally a small taper along the length of the pad as the rotor tries to drag the pad in the direction it is turning. Some of the high performance multi piston calipers now use different diameter pistons to try to counteract this affect.
Differences in thickness in a single pad of more than 0.5mm can indicate a problem with the caliper requiring a caliper service, recondition of replacement. Even if the pads have worn evenly with no taper they can still tell a story. The differences in thickness between pads can also indicate caliper problems.
Some examples are:
Outer pads worn more than inner pads in single piston floating calliper can indicate the floating caliper is binding on its slides either through excessive wear or lack of lubrication, so after a brake application the pistons retracts but the outer pad is still held in contact with the disc. To help prevent binding, always clean the caliper slides with Bendix Brake Cleaner, and lubricate with Bendix Brake Lubricant.
Wear of both pads on one side of the vehicle could indicate the piston is unable to retract, possibly due to corrosion or a damaged rubber piston boot. If the piston is unable to retract, both the pads will be left contacting the disc after each brake application causing rapid wear, the driver may experience the vehicle pulling to the damaged side for a while after the brakes are released. In extreme cases of piston binding the piston may not be able to move at all, causing the opposite wheel to do much more of the braking, wearing its pads, prematurely and potentially causing the opposite wheel to do much more of the braking, wearing its pads prematurely and potentially causing the vehicle to pull to one side during braking. To help prevent corrosion, always bleed plenty of the old heat affected brake fluid out during a brake job and top up with quality Bendix brake fluid.
Links:
www.bendix.com.au
www.bendix.com.au/performance
