We replace the sealing ring if there are traces of brake fluid leakage in the brake mechanism.
We show the replacement of the boot and sealing ring on the front wheel brake cylinder. The boot and sealing ring on the rear wheel brake cylinder are replaced in the same way.
We remove the front wheel.
Disconnect the lower end of the brake hose from the caliper (see Replacing the front brake hose).
Remove the brake pads (see Replacing the front brake pads).
Using a 14 mm open-end wrench, unscrew the upper bolt securing the caliper to the guide pin…
...and remove the caliper.
We remove the piston from the caliper.
To remove the piston, you can apply compressed air from a tire pump through the hole in the caliper.
We remove the protective cover from the support.
We pry off the sealing ring with a screwdriver…
…and remove the ring from the caliper.
We install a new sealing ring. We insert a new protective cover into the caliper groove.
Apply brake fluid to the working surface of the sealing ring and the surface of the piston. To install the piston, clamp the caliper in a vice with soft metal jaw pads. To put the protective cover on the piston, attach the hose of the tire pump or compressor to the caliper hole.
We supply air to the cylinder and bring the piston bottom to the edge of the cover, centering it relative to the cover.
Under the action of air pressure, the cover straightens out and is placed on the piston, which is inserted into the cylinder.
If there is no pump to put the cover on the piston, you will need an assistant who should lift the cover by the edge (inserted into the groove of the caliper) and stretch it so that a piston can be inserted inside.
Having put on the cover, we center the piston..
…and, pressing on it with a wooden block, we press the piston into the caliper.
We assemble the brake mechanism in the reverse order.
We bleed the hydraulic drive of the brake system (see Bleeding the hydraulic brake system).