1997-2001 Honda CR250 – Front Master Cylinder Service

May 30, 2018

How To Rebuild The Front Master Cylinder On Your 97-01 Honda CR250

The Tools You Will Need

The Parts You Will Need

This rebuild should cost no more than $25, and less than one hour to complete.

Pre-Service Notes

Brake fluid will damage almost everything, so keep your shop towels handy.
Start by removing the master cylinder from your bike.
Loosen and remove the banjo bolt, and wrap the end of your brake line with a shop towel, then remove the mounting bolts.

Completely disassemble the master cylinder, starting with the brake lever pivot bolt and spring.
Remove the piston boot and reservoir cap.
The snap ring holding the piston can be challenging to get too, so use your pick, and take your time.

Clean every piece of the system, and inspect them for excessive wear.
When cleaning brake components, all you need to use is clean brake fluid and a stiff brush.
If your master cylinder is rusty, some sanding and cleaning with carb cleaner are needed. Just make sure so rinse and dry every component, then clean again with fresh brake fluid.
Clean every piece of the system, and inspect them for excessive wear.

Measure the inside diameter of the cylinder bore and the outside diameter of the piston.
The cylinder bore should measure no greater than 11.05mm, and the piston should measure no less than 10.84mm.
The piston is within spec, and the cylinder bore is just under the service limit, so this master cylinder is good to go.

While everything is drying, take stock of your new parts. I am installing an All Balls front master cylinder rebuild kit, and you can get this exact kit HERE!
This kit comes with a piston boot, piston seals, reservoir cap screws, piston washer, banjo bolt seal washers, spring clip, and piston return spring.
Match the old parts with the new parts to make sure you’re not accidentally throwing away something you need.
Once you have your new parts ready, soak your new piston cups in fresh brake fluid for 15 minutes to soften and lubricate for assembly.
This kit comes with a piston boot, piston seals, reservoir cap screws, piston washer, banjo bolt seal washers, spring clip, and piston return spring.

Make sure to use brake fluid throughout the install to lubricate your parts
Start your assembly with the piston. Install the large piston cup on the lever end and the small cup on the spring end.
Make sure to install the cups, so the wide side is facing the spring end.
Attach the new spring.
Install the piston past the first cup, and stop when the spring touches the end of the cylinder.
The piston and cylinder are a very tight fit, so take care not to roll the piston cups on the way in.
Get your piston washer and spring clip in position, then hold the master cylinder in your left hand and carefully press the piston into the bore with your thumb.
While holding the piston down, seat the washer, and install the spring clip.
If your spring clip has a flat side and a rounded side, the flat side must face out.
Grease and install the boot. You can use the round end of a small wrench to push the sides of the boot all the way into the bore.
Wipe off the excess grease, and install the brake lever spring and pivot bolt.
Finally, install the reservoir cap.