K&L 32-4228 14mm Rear Master Cylinder Rebuild Kit for Triumph
The K&L 32-4228 kit rebuilds the 14mm rear brake master cylinder used on many Hinckley Triumph motorcycles from the early 1990s on, including Bonneville, Thruxton, Speed Triple, Street Triple, Daytona, Tiger, Sprint, Trophy, Thunderbird, America, Speedmaster, and Rocket III models. It replaces Triumph part number T2020031. If your rear brake pedal feels soft or sinks, the master cylinder leaks fluid, or the piston has seized after the bike sat, this kit brings the original master cylinder back to working order without buying a complete new unit.
K&L Supply sources its master cylinder kits from the original equipment manufacturers, and this one is made in Japan. The rear master cylinder converts the push of your brake pedal into the hydraulic pressure that makes the caliper clamp the disc. Once the internal seals wear, harden, or swell, that pressure leaks away. New seals and a new piston assembly restore firm, consistent braking.
Specifications
- Manufacturer: K&L Supply
- K&L part number: 32-4228
- British Iron part number: MBI-324228
- Replaces Triumph OEM part: T2020031
- Master cylinder bore: 14mm
- Position: Rear brake
- Country of manufacture: Japan
- Shipping weight: 0.2 lb
Signs Your Rear Master Cylinder Needs a Rebuild
- The rear brake pedal feels soft or spongy, or slowly sinks under steady pressure, even after bleeding.
- Brake fluid is weeping from behind the dust boot, where the pushrod enters the master cylinder.
- The fluid level in the rear reservoir keeps dropping, but the caliper and hose aren’t leaking.
- The pedal won’t return fully, or the rear brake drags because the piston is sticking.
- The bike has been in storage and the reservoir has dark, sludgy, or crystallized fluid in it.
What the Rebuild Kit Does
This kit replaces the internal wear parts of the master cylinder: the piston and its seals, the return spring, the snap ring that holds the piston in the bore, and the rubber dust boot. These are the parts that wear out, harden with age, or get damaged by old, contaminated fluid. K&L kits contain the components needed to fully rebuild the master cylinder internals. They do not include the master cylinder body, reservoir, reservoir cap or diaphragm, hoses, or brake fluid.
Fitment for this 14mm Rear Master Cylinder Rebuild
- 96-01 Adventurer
- 02-20 America
- 01-20 Bonneville
- 92-20 Daytona
- 98-01 Legend TT
- 06-18 Rocket III
- 06-20 Scrambler
- 19-20 Scrambler 1200
- 02-05 Speed Four
- 94-20 Speed Triple
- 02-20 Speedmaster
- 93-20 Sprint
- 17-20 Street Cup
- 17-20 Street Scrambler
- 07-20 Street Triple
- 16-17 Street Twin
- 04-20 Thruxton
- 95-20 Thunderbird models
- 93-18 Tiger
- 91-98 Trident
- 91-04 Trophy
- 00-03 TT600
See the “Fit for the Following Vehicles” tab for the complete year, make, and model list. To confirm fitment, check that your rear master cylinder is the 14mm unit sold under Triumph part number T2020031. If you have changed to an aftermarket rear master cylinder, this kit will not fit it.
Rebuilding a Triumph Rear Master Cylinder
Follow the brake section of the service manual for your model for removal, torque values, and bleeding. The basic steps:
- Protect painted and plastic surfaces from brake fluid, then drain the rear system and remove the master cylinder from the bike.
- Pull back the rubber dust boot and remove the snap ring with thin snap ring pliers.
- Slide out the old piston, seals, and spring. If the piston is stuck, cover the master cylinder with a shop rag and use a short burst of compressed air through the hose port. Never use your hand to catch the piston.
- Clean the bore with brake cleaner, make sure the reservoir ports are clear, and check the bore for pitting or scoring. If the bore is damaged, the master cylinder must be replaced, because new seals will not seal against a pitted bore.
- Coat the new piston, cups, and seals with clean brake fluid, then reassemble. Make sure the snap ring is fully seated in its groove and the new dust boot is seated properly.
- Reinstall the master cylinder, refill with fresh brake fluid, bleed the rear brake, and check pedal free play and the brake light switch before you ride.
For a detailed walk-through with photos and tips for bikes with dried-up fluid, read Mike Grage’s Triumph Hydraulic Brake Restoration guide. You’ll find snap ring pliers and other workshop tools in our service tools collection.
Related Rear Brake Parts
If you are rebuilding the master cylinder on a high-mileage or long-stored bike, now is a good time to check the rest of the rear brake system. Browse the Triumph brakes collection for rear brake pads, rotors, and stainless braided hoses, including the EBC rear brake hose for Thunderbird and Adventurer and the Venhill rear brake hose for America and Speedmaster.
*The product images shown are for illustrative purposes only and may not be an exact representation of the product received. Manufacturers occasionally make minor cosmetic changes to items, such as color, finish, label, or design. These changes do not impact the item’s function or compatibility. Please contact us if you have specific concerns regarding appearance.
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Frequently Asked Questions
What does the K&L 32-4228 rebuild kit fit?
It rebuilds the 14mm rear brake master cylinder on many Hinckley Triumph models, including the Bonneville, Thruxton, Scrambler, Speed Triple, Street Triple, Daytona, Tiger, Sprint, Trophy, Thunderbird, America, Speedmaster, Rocket III, Trident, Adventurer, Legend TT, Speed Four, and TT600. Check the fitment list and the “Fit for the Following Vehicles” tab for your year and model.
What Triumph part number does this kit replace?
It replaces Triumph part number T2020031, the 14mm rear master cylinder repair kit. The K&L part number is 32-4228, and the British Iron part number is MBI-324228.
How do I know if my rear master cylinder needs rebuilding?
Common signs are a soft or sinking rear brake pedal that bleeding doesn’t fix, fluid leaking from behind the dust boot, a reservoir level that keeps dropping with no leak at the caliper or hose, or a piston that sticks and makes the brake drag. A bike that has sat with old fluid in the system almost always needs a rebuild.
What parts are included in the kit?
The kit contains the internal parts needed to rebuild the master cylinder: the piston with its seals, the return spring, the snap ring, and the dust boot. It does not include the master cylinder body, reservoir, cap or diaphragm, hoses, or brake fluid.
Is the K&L kit as good as the Triumph OEM kit?
K&L Supply sources its master cylinder rebuild kits from the original equipment manufacturers, and this kit is made in Japan. It’s built to the same specification as the factory kit and usually costs less than buying the T2020031 kit from a dealer.
Is it better to rebuild or replace the rear master cylinder?
If the bore is clean and smooth, rebuilding with this kit restores full function for much less than a new master cylinder. If the bore is pitted, scored, or corroded, the new seals cannot seal properly, and you should replace the master cylinder.
How hard is it to rebuild a Triumph rear master cylinder?
It’s a straightforward job for a home mechanic with basic tools, thin snap ring pliers, brake cleaner, and fresh brake fluid. Remove the master cylinder, take out the dust boot, snap ring, and old piston, clean and inspect the bore, then install the new parts coated in brake fluid and bleed the system. Mike Grage’s Triumph hydraulic brake restoration guide covers the process in detail.
What brake fluid should I use after the rebuild?
Use the fluid listed on your reservoir cap and in your service manual, which is DOT 4 for Triumph. Some owners switch non-ABS bikes to silicone DOT 5. That switch requires a full flush and new seals throughout the system, and DOT 5 should not be used in ABS systems.
Do I need special tools to rebuild the master cylinder?
You need snap ring pliers with tips thin enough to fit between the piston and the master cylinder body. A small pick for the dust boot, brake cleaner, and compressed air are also helpful. Browse British Iron’s service tools for workshop tools.
Does this kit fit the front brake or clutch master cylinder?
No. This kit is for the 14mm rear brake master cylinder only. Front brake and hydraulic clutch master cylinders use different bore sizes and need their own rebuild kits.
Should I replace anything else while the rear brake is apart?
On an older or long-stored bike, inspect the rear brake hose, caliper seals, pads, and rotor. Dried or cracked rubber hoses are a common upgrade point for stainless braided lines. See the Triumph brakes collection for rear pads, rotors, and hoses.
Does this kit work on ABS-equipped Triumphs?
Yes, as long as your bike uses the 14mm T2020031 rear master cylinder listed in the fitment. On ABS models, follow the service manual’s bleeding procedure and stay with the specified DOT 4 fluid.
