We replace the sealing ring if there are traces of brake fluid leakage in the brake mechanism.
We remove the front wheel.
Disconnect the lower end of the brake hose from the caliper (see Replacing the front wheel brake hose).
Pushing the piston into the cylinder (see Replacing the brake pads of the front wheels).
Using the "14" head, unscrew the lower and upper bolts securing the caliper to the guide pins..
... and remove the caliper.
Remove the piston from the caliper.
To remove the piston, you can apply compressed air from the tire pump through the hole in the caliper.
Remove the protective cover from the caliper.
We take out the piston sealing ring by prying it with a screwdriver.
We replace the sealing ring and the protective cover with new ones.
We apply brake fluid to the working surface of the sealing ring and the surface of the piston.
To install the piston, we clamp the caliper in a vice with soft metal jaws, center the piston and press on its bottom with a hammer handle, sinking the piston into the caliper.
We assemble the brake mechanism in the reverse order and pump the brake hydraulic drive.