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 brake hose).
We press the piston into the cylinder (see Replacing the brake pads of the front wheels).
Using a 14 mm head, unscrew the lower and upper bolts securing the caliper to the guide pins…
...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 remove the piston sealing ring by prying it up with a screwdriver.
We replace the sealing ring and protective cover with new ones.
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 jaw pads, center the piston and press on its bottom with the handle of a hammer, pressing the piston into the caliper.
We assemble the brake mechanism in the reverse order and bleed the brake hydraulic drive.