2009-2010 Honda CRF450r – Rear Master Cylinder Service

How To Service The Rear Brake Master Cylinder On Your 2009 – 2010 Honda CRF450r.

2009 - 2010 Honda CRF450r - Rear Master Cylinder Feaured ImageThe 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.

Brake fluid will damage almost everything it touches, so make sure you have your shop towels handy!

Related: 2009-2010 Honda CRF450r – Rear Caliper Service

Click Here To Open Brake Specs In A New Window

Rear Master Cylinder Removal:

(Click to Enlarge)
Start by unbolting the brake lever, and removing the brake lever spring.  Remove Brake Lever Spring
Loosen the banjo bolt while the master cylinder is still mounted.Loosen The Rear Master Cylinder Banjo Bolt
Remove the mounting bolts, followed by the banjo bolt.Remove Mounting Bolts

Remove the Banjo Bolt From The Rear Master Cylinder

Make sure to wrap the end of the brake line with a paper towel.Wrap Brake Line In Shop Towel

Rear Master Cylinder Disassembly:

Completely disassemble the master cylinder.
Undo the brake lever clevis lock nut, and set the lever assembly aside.2009 - 2010 Honda CRF450r - Rear Master Cylinder - Remove Brake Lever From Pushrod
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.Remove Reseroir Cap And DiaphragmRemove The Rear Master Cylinder BootRemove Spring Clip And Pushrod Remove The Rear Master Cylinder Piston


Related: 2009-2010 Honda CRF450r – Front Caliper Service

Clean And Inspect:


Scrub every part inside and out with brake cleaner and a shop towel.

2009 - 2010 Honda CRF450r - Rear Master Cylinder - Clean EverythingIf you need to scrub anything, make sure you use a non-metallic brush.


Inspect every component for damage or uneven wear.

If you find any rough spots, gently sand them down with fine-grit emery paper.


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

Measure The Rear Master Cylinder Piston Bore Measure Piston

The cylinder bore should be no Greater than 9.575mm, and the piston should be no LESS than 9.465mm.

If your cylinder bore and piston are out of spec, they need to be replaced.

New Rear Master Cylinder Parts:

Before assembly, take stock of your new parts.

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.

New Rear Master Cylinder Parts From All Balls Racing Make sure to match the old parts with the new parts, so you don’t throw away something you need unintentionally.

Soak your new piston cups in fresh brake fluid for about 15 minutes before assembly.Soake New Parts For 15 Minutes

Rear Master Cylinder Assembly:

(Click to Enlarge)
Start your assembly with the piston. Install the piston cups with the large side facing the spring end.

Take your time with the cups; if they are damaged during install, your brakes won’t work.

2009 - 2010 Honda CRF450r - Rear Master Cylinder - Install Piston Cups
Install the piston spring.Install 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.

Install The Rear Master Cylinder Piston
To install the pushrod, start by holding the cylinder body with your left hand.

Apply a layer of rubber grease to the pushrod, then position the push rod and spring clip.

Apply Rubber Grease To Pushrod
Firmly press the pushrod down with your left thumb, and clip the pushrod into place.Install Spring Clip
To make sure the clip is in the groove, use your pick to rotate it. If it moves, it’s seated.Rotate Clip with Pick
Apply some rubber grease to the inside of the new boot, and slip it over the pushrod.

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.

Wipe off any excess grease.

Install Pushrod Boot
Install the diaphragm and reservoir cap.Install The Rear Master Cylinder Diaphragm And Cap

Rear Master Cylinder Installation:

Install the banjo bolt with the new seal washers, and make sure the shank rests on the tab.
Install the master cylinder mounting bolts.Install Mounting Bolts
Install the brake lever and attach the return spring. After your rebuild, make sure to bleed the rear brake system!Install Brake Lever Pivot BoltAttach Brake Lever Spring

Rear Master Cylinder Torque Specs:

Mounting Bolts10 ft-lbs
Banjo Bolt25 ft-lbs
Pivot Bolt27 ft-lbs


Keep Your ’09-’10 CRF450r Running Right!

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

This site uses Akismet to reduce spam. Learn how your comment data is processed.