RULES OF INSPECTION

• Never judge the condition of the brake pads using just one pad. Both pads and their thicknesses need to be inspected and documented.

• Never take rust or corrosion lightly. Corrosion on the caliper and pads is an indication the coating, plating or paint has failed and needs to be addressed. Corrosion can migrate to the area between the friction material and backing plate.

• Some brake pad manufacturers bond the friction material to the backing plate with adhesives. Delamination can occur when the corrosion gets between the adhesive and friction material. At best, it can cause a noise problem; at worst, the corrosion can cause the friction material to separate and reduce the effective area of the brake pad.

• Never ignore the guide pins, boots or slides. It is rare to find a caliper that has worn out the brake pads without wear or degradation also taking place on the guide pins or slides. As a rule, when the pads are replaced so should the hardware.

• Never estimate life or thickness using percentages. It is impossible to predict the life left in a brake pad with a percentage. While most consumers might be able to understand a percentage, it is misleading and often inaccurate. In order to accurately estimate the percentage of material worn on a brake pad, you would first have to know how much friction material was present when the pad was new.

Every vehicle has a “minimum wear specification” for the brake pads, a number typically between two and three millimeters.

NORMAL WEAR

No matter the caliper design or vehicle, the desired outcome is to have both brake pads and both calipers on an axle wear at the same rate.

If the pads have worn evenly, it is proof that pads, calipers and hardware have functioned properly. However, it’s not a guarantee that they will operate the same way for the next set of pads. Always renew the hardware and service the guide pins.

OUTER PAD WEAR

Conditions that cause the outer brake pad to wear at a higher rate than the inner pads are rare. This is why wear sensors are rarely put on the outer pad. Increased wear is typically caused by the outer pad continuing to ride on the rotor after the caliper piston retracts. This could be caused by sticky guide pins or slides. If the brake caliper is an opposed piston design, outer brake pad wear is an indication the outer pistons have seized.

INNER PAD WEAR

Inboard brake pad wear is the most common brake pad wear pattern. On a floating caliper brake system, it is normal for the inner to wear faster than the outer – but this difference should only be 2-3 mm.

More rapid inner pad wear can be caused by a seized caliper guide pin or slides. When this occurs, the piston is not floating, and equalizing force between the pads and the inner pad is doing all of the work.

Inner pad wear can also occur when the caliper piston is not returning to the rest position due to a worn seal, damage or corrosion. It can also be caused by a problem with the master cylinder.