1997-2001 Honda CR250 – Rear Master Cylinder Service

How To Rebuild The Rear Master Cylinder On Your 1997 – 2001 Honda CR250

1997 - 2001 Honda Cr250 - Brakes - Rear Master Cylinder FeaturedThe Tools You Will Need Are:

  • 5mm Hex Wrench
  • 8mm Hex wrench
  • 12mm box wrench
  • 12mm socket
  • Torque Wrench
  • Long Nose Snap Ring Pliers
  • Regular Pliers
  • Needle Nose Pliers
  • Calipers
  • Rubber Grease
  • Shop towels
  • And Safety Glasses

The Parts You Will Need To Service Your Rear Master Cylinder:

  • New ’97-’01 Honda CR250 Rear Master Cylinder Rebuild Kit
  • New Cotter Pin
  • Fresh DOT 4 Brake Fluid

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

Related: 1997-2001 Honda CR250 – Bleed Brake System

Click Here To Open Brake Specs In A New Window

Removal

Brake fluid will damage almost everything, so keep your shop towels handy. Be Careful!
Start by disconnecting the brake pedal return spring.      1997 - 2001 Honda Cr250 - Rear Master Cylinder - Removal - Return Spring
Remove the banjo bolt, and keep track of the seal washers.Removal - Banjo Bolt
Remove the brake fluid reservoir bolt.Removal - Reservior
Remove the master cylinder mounting bolts.Removal - Master Cylinder Mounting Bolts
Pull the unit away from the frame.Removal - Pull Away From Frame
Remove the brake lever pivot bolt, then pull the entire master cylinder assembly.Removal - Brake Lever Pivot BoltRemoval - Pull Assembly

Rear Master Cylinder Disassembly

When you take the entire assembly off your bike, you can remove the clevis cotter pin much faster. Even with the assembly off the bike, I still had a hard time pulling this cotter pin.        1997 - 2001 Honda Cr250 - Rear Master Cylinder - Disassembly - Cotter Pin
With the brake pedal disconnected, remove the clevis and lock nut from the push rod shaft.Disassembly - Clevis
Remove the reservoir and hose from the cylinder body.Disassembly - Reservior Hose
Remove the snap ring and reservoir hose mount.Disassembly - Hose Mount ClipDisassembly - Hose Mount
Pull the boot from the pushrod shaft, then remove the snap ring.Disassembly - Pushrod BootDisassembly - Pushrod Clip
Pull the pushrod and washer from the cylinder.Disassembly - Pushrod And Washer
Pull the piston and the spring. Remove the spring and cups from the piston.Disassembly - Piston
Finally, disassemble the reservoir and hose.Disassembly - Reservior and Hose

Clean & Inspect

Clean every piece of the system and inspect them as you go. When cleaning brake components, all you need to use is clean brake fluid and a stiff brush.

But this master cylinder was so rusty, this went from routine service to a full restoration, so I had to clean it with something harsher than brake fluid.

So after I scrub all the grime and sand off all the rust, I’m going to have to thoroughly rinse and dry every component, then clean again with brake fluid, to remove any residue.

Related: How To Reverse Bleed The Brake Systems On Your Dirt Bike

Measure

Measure the inside diameter of the cylinder bore, and the outside diameter of the piston.

The cylinder bore should measure no greater than 12.76mm, and the piston should measure no less than 12.64mm1997 - 2001 Honda Cr250 - Rear Master Cylinder - Measure Piston 1997 - 2001 Honda Cr250 - Rear Master Cylinder - Measure Cylinder

This cylinder bore is 12.77mm, and the piston is 12.59mm, which means this is out of spec by .06mm.

I’m going to take my chances and keep using these parts. If you want reuse out of spec parts, I didn’t tell you to do it.

New Parts

While everything is drying, take stock of your new parts. I am installing an All Balls master cylinder rebuild kit number 1439440002.

1997-2001 Honda Cr250 - Brakes - Rear Master Cylinder - New parts

This kit comes with a new spring, boot, reservoir o-ring, piston clip, piston cups, reservoir clip, and banjo bolt washers.

Get Your Rebuild Kit Here

Make sure to 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 o-ring and piston cups in fresh brake fluid for 15 minutes to soften and lubricate for assembly.

1997 - 2001 Honda Cr250 - Rear Master Cylinder - Soak New RubberRelated: 1997-2001 Honda CR250 – Top End Rebuild – Introduction

Assembly
Start your assembly with the piston.
Make sure to use brake fluid throughout the install to lubricate your parts Be Careful!
Install the large piston cup on the push rod end and the small cup on the spring end.   1997 - 2001 Honda Cr250 - Rear Master Cylinder - Assembly - Piston Cups
Make sure to install the cups, so the wide side is facing the spring end. Be Careful!
Attach the new spring.Assembly - Piston Spring
Install the piston past the first cup, and stop when the spring touched the end of the cylinder.Assembly - Piston Into Cylinder
The piston and cylinder are a very tight fit, so take care not to roll the piston cups on the way in.Be Careful!
Coat the push rod end with rubber grease, and hold to the push rod to the piston while you get the spring clip in position on the push rod shaft.Assembly - Grease Piston EndAssembly - Hold Pushrod
Grip the cylinder in your fist, and hold the push rod with your thumb.Assembly - Place Clip
Carefully press the push rod down into the cylinder until the washer passes the spring clip groove, and install the spring clip.Assembly - Install Clip
If your spring clip has a flat side and a rounded side, the flat side must face out.Be Careful!
Grease and install the boot.   Assembly - Grease Boot
You can use the round end of a small wrench to push the sides of the boot all the way into the bore.Assembly - Install Boot
Install the lock nut and clevis.Assembly - Clevis
Adjust the clevis so the center of the first mounting hole, and the center of the clevis hole are 75mm apart.Assembly - Measure Mounting Hole and Clevise Hole
Install the new o-ring for the reservoir hose mount.Assembly - Hose Mount O-ring
Install the hose mount, and secure it with the spring clip.Assembly - Hose Mount Clip
If your spring clip has a flat side and a rounded side, the flat side must face out.Be Careful!
The hose mount may feel loose, but the pressure in the system will push it tight to the clip.
Assemble and install the reservoir and hose.Assembly - Hose
Reassemble the brake lever and clevis with a new cotter pin.Assembly - Cotter Pin
Rear Master Cylinder Installation
Install the brake lever and master cylinder, then push the reservoir into the frame.97-01 CR250 - Rear Master Cylinder - Install - Brake Lever Pivot Bolt Install - Master Cylinder Mounting Bolts Install - Reservoir Into Frame
Do not attach the reservoir; you will need access to fill it when replacing brake fluid.Be Careful!
Install the banjo bolt with the new seal washers, and reattach the return spring.Install - Banjo BoltInstall - Return Spring
Torque Specs
Banjo Bolt25 ft-lbs
Master Cylinder Mounting Bolts9 ft-lbs
Brake Lever Pivot Bolt19 ft-lbs
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Keep Your ’97-’01 CR250 Running Right!

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