REBUILDING FRONT BRAKE CALIPERS

A motorcycle is a compilation of many systems. Each of these systems is important and for me I hold the tires and brakes as equal in importance. The parts shown here are off a 1985 Honda VF00C with 75,000 miles of minimal maintenance. The bike, weathered and dirty, is complete, straight, and runs quite well, so the owner is justified in spending money to repair an older bike.

We put a new tire on the rear, changed and flushed the coolant, rebuilt the front forks, and lastly, rebuilt the front brakes. The first picture is the left caliper and that was the side the seal leaked worse.  

The second picture is the right caliper and is just dirty with cooked on mung.

The third picture shows both calipers disassembled.

 

A word about skill level here. Hydraulic systems like being clean. Don’t clean rubber parts with anything other than soapy water before reassembly. There are lots of parts to be careful with and those include the pistons. The pistons live a hard life. They have to move in and out under stressful conditions. Heat, water, dust, brake dust, and sometimes, high frequency vibration. Most of the time the degree of difficulty required to remove them from the caliper body is inversely proportional to the overall condition of the caliper. The dirtier and more abused it looks, including rust, the harder it will be to remove them. A C-clamp, good air supply, air gun, penetrating oil, and patience should be used with no discretion. These particular calipers had mostly dirt coating the pistons, so cleaning as much as possible before disassembly eased the process. I use an old tooth brush. Spray the entire completely disassembled caliper with a soapy solution and rinse with hot water.

If the caliper has two pistons use a C-clamp to hold one piston and blow air into the caliper body. If you’re lucky it will pop out. If it sticks, use the clamp to push the piston back in a little after spraying the penetrating oil around the piston. Back and forth…in…out…in…out and eventually both popped out.

The piston pictured had a nick towards the outer edge. I used a fine diamond file to remove the ridge and then a piece of worn 800 grit with oil to polish the piston. If the piston has corrosion pits, then I would suggest replacing the piston. I used the same piece of paper to polish the piston and remove any baked on residue.

The stripped calipers are then taken to a solvent tank and cleaned of oil and grease residue. Then I take the calipers to the glass bead cabinet and clean all the inside of the caliper including the piston bore. After this process the calipers undergo another cleaning with soapy solution and hot water. After washing, it now time for reassembly.

At this point it is extremely important to dry the caliper. Using an air gun and a contact cleaner, blow dry and all passages. Pour new brake fluid into the bores and rotate the caliper to insure the o-rings grooves are coated. Carefully install the o-rings into the bores and apply more new brake fluid to them. Using my finger, I feel the rings and feel if they are even. Confident that they properly installed, I place the brake fluid coated pistons into the bore and using my fingers only, I press the pistons into the bores. This step is a touchy feely moment. If you did everything correctly, the pistons will slide to the bottom of their bore with gentle positioning. DO NOT FORCE THE PISTONS! If they resist then remove, inspect, relube and try again.

I finish installing the brake pads and pin holders to complete the job. After cleaning the wheel and removing all traces of oil residue from the brake rotors the calipers are reinstalled and  the system bled.