4 Pots Brake Caliper GT4 Fit 345*28mm Brake Disc Rotor For BMW

WHAT GOES WRONG?
A caliper will typical leak between the piston and seal or the piston will seize in the caliper bore causing the brake to lock up and not release. This is caused by the caliper piston developing rust and corrosion near housing seal. Leaks are caused by moister and dirt in the brake fluid which damages the rubber caliper piston seal. When the piston is reset (pushed back inward into the caliper housing) to except the new brake pads it can damage the seal and cause a leak. The seal should be okay for the first or second pad replacement. There are three reasons to replace the caliper, the first and most obvious is a fluid leak, the second is to prevent a leak due to age and the third is the piston is seized causing irregular braking or pad wear characteristics. A leak will cause the brake system warning light to come on because of the low fluid level in the master cylinder reservoir.

Symptoms of a Bad Brake Caliper
Fluid leak
Overheating brakes
Car pulls either to the right or left when applying the brakes
Uneven brake pad wear
Brakes not releasing

HOW DOES IT WORK?
A brake caliper is designed to utilize brake fluid under pressure to transfer hydraulic force from the brake master cylinder to the brake pads. The brake pads then contact the rotating brake rotor to slow the car through friction. A brake caliper is typically mounted to the caliper mount which embodies two caliper slides.

There are two basic designs of brake caliper mounting, fixed and floating. A fixed position brake caliper is bolted to the mount and is not allowed to move. This kind of design is constructed with one piston on either side of the caliper. The floating style of caliper which is more common is mounted to the caliper mounting bracket using slide bolts which allow the caliper to "float" as the brake pads wear, this design uses pistons on one side of the caliper. Brake calipers can have from 1 to 6 pistons depending on the manufacturer's design.

All brake calipers are fitted with a brake fluid bleeder which allows air to escape from the system. If air is allowed in the system it can cause a spongy brake pedal. A brake caliper piston is sealed to the brake caliper housing using a main piston seal. This seal allows the piston to move back and forth without allowing brake fluid to leak and is protected by a dust seal that helps keep debris from contaminating the integrity of the main seal.