2009-2010 Honda CRF450R – Front Master Cylinder Service

Jun 22, 2018

How To Service The Front Brake Master Cylinder On Your 2009 – 2010 Honda CRF450R

The Tools You Will Need Are:

The Parts You Will Need Are:

This front master cylinder rebuild should cost around $25 and take approximately 30 minutes to complete.

Pre-Service Notes

Completely disassemble the master cylinder.
Be careful when removing the snap ring; the piston is under pressure and will jump out at you.

Clean

Inspect every component for noticeable damage.
If you find any rough spots, gently sand it down with fine-grit emery paper. I always give the pivot bolt and the pushrod a once over to be safe.

Measure the inside diameter of the cylinder bore and the outside diameter of the piston.
The cylinder bore should be no Greater than 11.05 mm, and the piston should be no LESS than 10.84 mm.
If your cylinder bore and piston are out of spec, they need to be replaced.

Before assembly, take stock of your new parts.
I am installing an All Balls rebuild kit that includes a new piston spring, pushrod boot, piston cups, spring clip, piston washer, and banjo bolt seal washers.
Make sure to match the old parts with the new ones, so you don’t accidentally throw away something you need.
Soak your new piston cups in fresh brake fluid for 15 minutes before assembly.

Front Master Cylinder Assembly

Start your assembly with the piston. Install the piston cups with the large side facing in.
Take your time with the cups; if they are damaged during install, your brakes will not work.
Install the new piston spring.
Coat the master cylinder bore with brake fluid, and install the piston past the first cup.
Install the piston in a twisting motion to avoid rolling the cups.
Place the piston washer and spring clip on the piston.
When installing the spring clip, ball up a piece of shop towel and place it in the pushrod, then push the piston down with a screwdriver to make room for the snap ring pliers.
This is the hardest part of assembly because you almost need three hands, and too many things are in too small of a space.
I find it easier to compress the spring clip before I push the piston down; that way the spring clip will stay level.
But be patient, and you will get it.
To make sure the clip is in the groove, use your pick to rotate it. If it moves, it’s seated.
Install the new boot on the pushrod. Pull the boot up and grease the pushrod, then place the pushrod in the piston.
Gently push the boot down into the bore.
Align the knocker arm with the pushrod, and install the brake lever spring, followed by the pivot bolt.
Carefully pull the boot up into the groove on the knocker arm.
Install the diaphragm and reservoir cap.