Brake Caliper Guide Pins
The brake caliper guide pins are two round metal pins on each brake caliper where the brake piston assembly sits. They’re called guide pins because they’re responsible for guiding the proper angle for how the brake pad meets the disc.
If the caliper is not free to move, the culprit might be bent or binding guide pins. Even if guide pins are not damaged, swollen or hardened guide seals or lack of lubrication may cause the caliper to bind resulting in uneven pad wear.
Always inspect all mounting surfaces and hardware for corrosion, wear or misalignment.
Caliper Guide Pin Boots
Most sliding calipers use a rubber or plastic insulator around the mounting bolts of the caliper. This sleeve of soft material loses resiliency over its lifetime. This is hastened by the high-temperature environment of the brakes.
As materials wear, instead of being round the pins are flattened by the torque from the brakes into an oval shape that can cause excessive caliper movement, which in turn, can cause noise like rattles and thumps even if the brakes are not applied. These rattles often stop when the brakes are applied.
Always inspect and replace if necessary any dust boots or guide pin inner sleeves that protect the caliper guide pins. If the soft parts look OK, clean out all the old lubricant and replace with new silicone grease.
Unlike steel, soft parts like rubber are sensitive to chemicals. Choosing the right lubricant for these parts is critical to ensuring the integrity of the part, we strongly recommend using only silicone grease, other lubricants will cause the rubber dust boots to swell and degrade. If the caliper boots fail to make a seal with the caliper carrier and bolt, water can be sucked into the cavity as the bracket contracts and cools.