Let’s take the KX125 as an example. In rebuilding the front brake system of your KX125, you can buy the calipers and master cylinders from Kawasaki, for dealers sell these as individual parts. First, release the brake-line banjo bolts, and then remove the master cylinder line and caliper from the bike. Next, remove the brake lever on the master cylinder to uncover its seal cover. Remove it carefully then work the E-clip piston stopper from the groove. Then remove the O-ring stopper and the piston assembly. Clean the master cylinder’s housing and body thoroughly.

Next coat the new master cylinder piston with brake fluid and insert into the master cylinder body. Reinstall the stopper, retainer clip, cover and brake lever. Fill the reservoir with fluid and bench bleed to remove air from around the piston. Reinstall the master cylinder on the handlebar.

Pop pucks from the caliper using safety glasses, rags and compressed air. Remove fluid seals and wipers from body, clean thoroughly and inspect caliper. Put new front seals and wipers, which should cost a lot less than a whole caliper. Install fitting grooves and coat new rubber bits with fluid. Fill the caliper with brake fluid partially with the banjo hole facing up, and then press pucks into their seal. Tap to remove air bubbles.

Finally, reinstall brake line to caliper, then inject new fluid through caliper bleed screw with the use of a syringe and tap the entire length to make sure there are no air bubbles. Install caliper on fork and route line to master cylinder. Refill line before fitting to master cylinder. Tighten the top banjo and pump the brake lever making sure to keep reservoir filled. Bleed until the sogginess disappears.