2009-2010 Honda CRF450R – Rear Master Cylinder Service

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

The Tools You Will Need Are:

• 12mm Socket
• 7mm Socket
• 12mm Wrench
• 10mm Wrench
• 8mm Wrench
• 8mm Hex
• 5mm Hex
• Small Pick
• Stiff Brush
• Long Nose Snap Ring Pliers
• Calipers
• Torque Wrench
• Shop Towels

The Parts You Will Need Are:

• ’09-’10 Honda CRF450r Rear Master Cylinder Rebuild Kit
• Dot 4 Brake Fluid
• Rubber Grease

This rear master cylinder rebuild should cost around $25 and take about 30 minutes to complete. If you don’t have your rebuild kit yet, you can get the one I am using HERE.

Pre-Service Notes

• I recommend opening the Service & Torque Specs in a new tab for easy reference.
• If you need parts and tools, make sure to buy them here!
• Pictures with captions are after the steps below.
• Brake fluid will damage everything, so keep your shop towels ready!
• If you need any help don’t hesitate to ask!

Rear Master Cylinder Removal

1. Start by unbolting the brake lever, and removing the brake lever spring.
2. Loosen the banjo bolt while the master cylinder is still mounted.
3. Remove the mounting bolts, followed by the banjo bolt.
4. Make sure to wrap the end of the brake line with a paper towel.

Rear Master Cylinder Disassembly

1. Completely disassemble the master cylinder.
2. Undo the brake lever clevis lock nut, and set the lever assembly aside.
3. The nut by the boot is part of the pushrod, so don’t try to remove it. It’s there to adjust the brake lever after installation.

Related: Now that you have your brake system rebuilt, you’ll need to install fresh brake pads.

Clean And Inspect

Clean

1. Scrub every part inside and out with brake cleaner and a shop towel.
2. If you need to scrub anything, make sure you use a non-metallic brush.

Inspect

1. Inspect every component for damage or uneven wear.
2. If you find any rough spots, gently sand them down with fine-grit emery paper.

Measure

1. Measure the inside diameter of the cylinder bore and the outside diameter of the piston.
2. The cylinder bore should be no Greater than 9.575mm, and the piston should be no LESS than 9.465mm.
3. If your cylinder bore and piston are out of spec, they need to be replaced.

New Rear Master Cylinder Parts

1. Before assembly, take stock of your new parts.
2. I am installing an All Balls Rear Master Cylinder Rebuild Kit that includes a new pushrod boot, banjo bolt seals washers, piston cups, spring clip and piston spring.
3. Make sure to match the old parts with the new parts, so you don’t throw away something you need unintentionally.
4. Soak your new piston cups in fresh brake fluid for about 15 minutes before assembly.

Rear Master Cylinder Assembly

1. Start your assembly with the piston. Install the piston cups with the large side facing the spring end.
2. Take your time with the cups; if they are damaged during install, your brakes won’t work.
3. Install the piston spring.
4. Coat the master cylinder bore with brake fluid, and install the piston past the first cup.
5. Install the piston in a twisting motion to avoid rolling the cups.
6. To install the pushrod, start by holding the cylinder body with your left hand.
7. Apply a layer of rubber grease to the pushrod, then position the pushrod and spring clip.
8. Firmly press the pushrod down with your left thumb, and clip the pushrod into place.
9. To make sure the clip is in the groove, use your pick to rotate it. If it moves, it’s seated.
10. Apply some rubber grease to the inside of the new boot, and slip it over the pushrod.
11. Push the boot into place with the round side of your 8mm wrench, and make sure the top of the boot seats in the groove past the nut.
12. Wipe off any excess grease.
13. Install the diaphragm and reservoir cap.

Related: Red rubber grease works great for brake pad pins, but it also makes tube installs way too easy!

Rear Master Cylinder Installation

1. Install the banjo bolt with the new seal washers, and make sure the shank rests on the tab.
2. Install the master cylinder mounting bolts.
3. Install the brake lever and attach the return spring. After your rebuild, make sure to bleed the rear brake system!

Rear Master Cylinder Torque Specs

• Mounting Bolts – 10 ft-lbs
• Banjo Bolt – 25 ft-lbs
• Pivot Bolt – 27 ft-lbs

If you have any questions or anything to add, please leave them in the comments or on our FaceBook page!

Keep Your ’09-’10 CRF450r Running Right!

• Service Specification
• Clutch Replacement
• Fuel System Service
• Engine Top End
• Brakes
• Exhaust
• Front Suspension & Steering
• Rear Suspension
• Wheels & Tires
• Kickstarter
• External Shift Linkage