Maintaining your dirt bike's brake system is crucial for optimal performance and safety on the track. In this 24MX workshop guide, I'll walk you through the process of bleeding both your front and rear brake systems. This maintenance task isn't just about changing fluid - it's about ensuring your brakes respond precisely when you need them most during racing.

Required Tools

Before starting any brake maintenance, it's essential to gather all the necessary tools and materials. You'll need a measuring jug and tubing for collecting the old brake fluid, along with the specific A9 racing oils dot4 brake fluid for refilling the system. Essential tools include an 8mm spanner for the bleed nipples, a 21mm spanner for the master cylinder cap, and plenty of clean rags for catching any spills. For accessing the rear brake, you'll also need a 6mm socket and cable ties for the frame guard work.

Tools needed:

• Measuring jug

• Tubing

• A9 racing oils dot4 brake fluid

• 8mm spanner

• 21mm spanner

• Rags

• 6mm socket (for frame guard)

• Cable ties

When to Change Your Brake Fluid

Understanding when to service your brake system is just as important as knowing how to do it. The most obvious sign is when your front brakes start feeling spongy, lacking that sharp, responsive feel you need for racing. For the rear brake, watch out for the pedal traveling further than usual before engaging. However, the most reliable indicator is the sight glass on your master cylinder.

Key indicators:
1. Brake Feel:

• When the front brakes go quite spongy

• If the rear brake pedal goes down a lot further than normal

2. Sight Glass Check:

• Look for the goldy texture color (indicates healthy fluid)

• If it's black and horrible, it's ready to remove

Front Brake Bleeding Process

The front brake bleeding process requires patience and attention to detail. The most critical aspect is maintaining the correct fluid level in the master cylinder throughout the entire process. There's a white pump at the bottom of the master cylinder that must always stay submerged in fluid - if it's exposed to air, you'll need to start the process over again. Position your bike on level ground before starting; this ensures the master cylinder stays perfectly flush and prevents unwanted fluid spillage.

Step-by-step process:
1. Initial Setup:

• Keep the bike nice and level

• Ensure master cylinder is flush (not dropping down, not too high)

• Remove the two bolts from master cylinder cap

2. Master Cylinder Important notes:

• There's a white pump at the bottom

• Never let fluid go too low or you'll drag air into the system

• Keep fluid topped up

• Never let go of brake lever during bleeding or it will suck air back

3. Bleeding Process:

• Remove rubber cap from black bleed nipple

• Insert tube onto bleed nipple, pushing right up to the 8mm bolt

• Place tube end in measuring jug, keeping it lower than bleed nipple

• Put thumb on front brake lever, push it into throttle grip

• Slacken off 8mm bolt while maintaining pressure

• Watch for tiny little bubbles (indicates air leaving system)

• Tighten before releasing brake lever ( and keep repeating this process )

• Put the master cylinder cap back on before removing the bleeding tube

• Check the rubber insert is clean with no dirt

• Make sure the 8mm bleed nipple bolt is nice and tight

• Have a rag ready as this part might get messy

• Remove the tube carefully, using thumb to catch any breakthrough

• Replace the rubber cap on the 8mm bleed nipple

• Test the brake to ensure nice and sharp pressure on the front brake lever

During this process, you might accidentally get brake fluid onto your brake disc. If this happens, don't worry - but it needs immediate attention as it will make your brakes squeaky and affect proper brake function. Simply get some brake cleaner and a rag, then give the disc a nice clean off to restore proper braking performance.

Rear Brake Process

The rear brake system follows similar principles to the front but requires additional steps due to the frame guard removal. Working with the rear brake requires extra attention to cleanliness, as its location makes it more susceptible to dirt and grit contamination. Take your time with the frame guard removal and reinstallation - these parts protect your brake system from debris during regular riding.

Sequential steps:
1. Frame Guard Removal:

• Remove 6mm bolt

• Cut cable tie

• Remove frame guard noting two little slots

• Clean area of dirt and grit

2. Master Cylinder:

• Use 21mm spanner for cap

• Check fluid through sight glass

• Fill fluid just above the sight glass window when finishing. During the process you can add a bit more

• Don't overfill - rubber insert will push fluid out

3. Bleeding Process:

• Same procedure as front brake

• Keep constant pressure on rear brake pedal

• Watch pedal arm drop when bleeding

• Monitor for bubbles in tube

Before reinstalling the frame guard, ensure your master cylinder is properly closed up. Don't overfill the fluid as the rubber insert from the lid will push it out, causing spillage. Fill just above the sight glass, then finger-tighten the lid first. Using your 21mm spanner, tighten it completely while keeping a rag handy for any potential overflow. Make sure it's nice and tight, but be careful not to overtighten. Finally, don't forget to reinstall the rubber cap on the bleed nipple - this crucial step prevents any dirt or grit from getting inside.

4. Frame Guard Reinstallation:

• Insert two little hook pieces into plastic first

• Hook piece goes into foot peg

• Hook frame guard down into place

• Install 6mm bolt (don't overtighten)

• Use cable ties through pre-existing holes

• Push cable tie around frame to tidy up

Important Safety Notes

Brake fluid maintenance requires careful attention to safety and cleanliness. Brake fluid can damage paint and surfaces, so keeping rags handy isn't just about tidiness - it's about protecting your bike. Always wear gloves to protect your skin, and keep brake cleaner nearby in case any fluid contacts your brake discs. Remember, contaminated brake discs can severely impact your braking performance.

Key safety points:

• Keep rags handy for overflow

• Avoid brake fluid on brake discs (use brake cleaner if contaminated)

• Wear gloves to avoid skin contact

• Keep fluid level topped up throughout process

• Clean rubber inserts before reinstalling

• Don't overtighten screws (they can snap)

Final Steps

Proper completion of the brake bleeding process is just as important as the procedure itself. Take time to verify all components are correctly tightened and secured. A properly bled brake system will give you a firm lever or pedal feel with immediate response - essential for confident riding on the track.

Final checklist:

• All bleed nipples are tight

• Rubber caps are secure

• Brake lever/pedal feel is firm

• No fluid leaks

• Frame guard is secure

Remember: Different bikes may require different brake fluids. Most use dot4 or dot5 but always check your specific bike's requirements. This A9 racing oils dot4 brake fluid can be found on the 24MX website.

By following these exact steps, you'll ensure your dirt bike's brake system is properly maintained and ready for racing. The process might seem detailed, but when done properly, it shouldn't take you long and will keep your brakes performing at their best.

Author information

My name is Charlie Frost, and I'm no stranger to the adrenaline-fueled world of extreme enduros. Starting my journey at 19, I seamlessly blended trials and enduro racing, honing my skills through youth events and extreme races like the Tough One and Erzberg. When I'm not tearing through rugged terrain, you can often find me in front of the 24MX camera, sharing my passion and insights with fellow riders, as we delve into the exhilarating world of off-road racing.