When to replace brake caliper

The majority of brake calipers need not be repaired or replaced the first time the brakes are relined. But the calipers could be approaching the end of the road after 75,000 miles, or 7 to 10 years of operation. The risk of sticking and leakage is increasing as the rubber seals age and harden. 
The caliper sticks or leaks will raises the chance of a comeback. Simply replacing the old calipers with new or remanufactured calipers is faster, quicker and cheaper. Loaded calipers are even better as they give you everything you need in one box and there is far less risk that the parts do not fit.

Replacement of the caliper is required if a caliper leaks brake fluid, a piston sticks or the caliper is worn or damaged. Leaks are very dangerous and should never be ignored because fluid loss can cause brake failure. 

Eventually leaks arise as the caliper ages and piston seals get rough and lose their elasticity. Corrosion can also accelerate seal wear within the piston bores or on the pistons themselves. When you move the pistons back into the caliper to add fresh pads, the piston seal will be forced to scrape through areas of the bore which may be rough with corrosion. If the caliper hadn't leaked before, it might start early.

​Caliper slides, pins, and bushings on floating calipers should also be checked carefully for wear, rust, cracks, or other damage. Using new sheets, bushings, and mounting hardware if you are removing a caliper and make sure to grease these parts with a high temperature, moisture-resistant brake lubricant.

If the slides or bushings are rusty, worn or damaged on a floating caliper, the caliper may not move freely causing uneven wear on the pads. A "sticky" or "frozen" caliper may also cause the brakes to drag if the caliper is not sliding so that the rotor can kick away from the outside pad. Because of the constant drag this can cause increased wear on the outer pad as well as a steering pull to one side. Set calipers do not suffer from this form of problem, since the caliper's location is set and the caliper is not moving. But when a piston gets jammed or trapped in its bore due to corrosion or swelling, both fixed and floating calipers will often "freeze up," or lock.

Either of two things may happen when a piston sticks: The brake may not apply or it may not detach. The uneven braking resulting from this will result in a hard pull to the "right" side when the brakes are applied, and/or a steering pull to the "bad" side when the brakes are removed. 

If you note uneven wear between the brake pads of the inner and outer wheels, it is a sure sign that the caliper (or caliper piston) sticks.

Calipers, particularly on high-mileage vehicles, should typically be replaced in pairs. However, if only one caliper needs to be replaced due to a leak or problem, the replacement caliper will have the same type of piston (steel or phenolic) as on the opposite side, as well as the same form of friction material (organic or semi-metallic nonasbestos). Side-to - side malfunctions can cause uneven braking. Other things that might be required to repair calipers include new brake hoses (fix if leaking, broken, brittle or worn), and brake fluid, definitely. Always flush the brakes to get rid of the old fluid, and bleed all the lines to get rid of any trapped air that could cause a soft pedal.
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