Seized brake caliper: what causes to seize and how to fix them

Have you noticed your car pulling to one side when braking, or taking longer than usual to come to a stop? Does it feel like you have to press the brake pedal down with much more force than before? Do you smell something burning after braking? The engine revs up slowly, and coasting has deteriorated? Perhaps it’s time to fix your brake caliper.

Brake caliper design

A caliper is an important element of a disc braking system serving to fasten and fixate brake pads, ensuring their mobility when braking. There are currently 2 kinds of calipers available: floating and fixed ones.

Floating calipers usually include one, sometimes two pistons located on one side of the brake disc only. The caliper housing is attached to the bracket fastened to the steering knuckle with bolts; brake pads are installed on the bracket.

Special springs are used to secure the pads inside the guide slots. As the brake pedal is pressed, the piston moves out of the cylinder and exerts pressure on the inner brake pad. After that the bracket moves along the guide pins and presses the outer pad to the disc.

The fixed caliper design does not include guide pins, while pistons are located on both sides of the brake disc. Thus when braking, the fluid under pressure is supplied to all cylinders simultaneously, causing both inner and outer pads to move. At other times they are held apart with spring spacers.

Why is my brake caliper sticking?

 Common reasons for a caliper sticking include: 

1. Exposure to humidity and dirt. The accumulated contaminations prevent the pistons and guide pins from moving freely. Liquid causes their corrosion, leading to sticking. If the rubber dust boots intended for protecting moving parts from aggressive environment leak, it increases risk of the pistons and pins breaking down. Sticking is also much more likely to occur if brake fluid is not changed on time: it is hygroscopic so its water content increases over time; this also leads to piston and pin corrosion.
2. Using the wrong lubricant or none at all. Special high-temperature resistant grease must be used on guide pins. Wrong grease tends to dry up or leak through; it can also destroy the rubber parts. The guide pin can’t move freely in a swollen bush.
3. Abrupt temperature changes. These have a detrimental effect on rubber dust boots. They accelerate corrosion and may cause the brake disc to bend, often leading to sticking brakes.
4. Worn caliper elements. A worn out caliper housing or piston surface causes it to skew and stick. The dirt accumulating in the damaged points impedes free travel of the moving parts.
5. Deformation. Guide pins may bend due to incorrect installation, high strains or careless driving; this also increases risk of sticking.
6. Driving with worn brake pads and discs. To ensure good grip of a worn friction pair, the piston may move out too far from its seat which may lead to its skewing.
7. Using the wrong brake fluid. If a fluid is too viscous, the pistons don’t return to their starting position. Besides, polymeric or composite pistons may swell when coming in contact with wrong fluid.  
8. Exposure to aggressive chemicals. Road grit and brake fluid cause premature wear of rubber dust boots, so it’s important to keep the system airtight at all times.

 5 tips on how to prevent brake calipers from seizing 

1. Replace the brake fluid in good time.
   A high moisture content in the brake fluid results in corrosion of the pistons.
2. Regularly check that the dust boots are in good condition.
   When they are damaged, dirt gets on the pistons.
3. Use the brake fluid recommended by the car manufacturer.
   With an excessively viscous fluid, the pistons return to their primary position slowly.
4. Lubricate the guide pins every six months.
   This will allow the moving parts of the assembly to move freely along their working path.
   
   
   Important! Use a special high temperature grease.
5. Clean the brake caliper.
   Remove dirt using brake cleaner and a wire brush.