How to: Flush Brake Fluid

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Categories: How To, Expert Advice, Repair and Maintenance

It may sound like another way for the “we do brake and muffler work” repair shop to swindle you into buying a replacement flux capacitor, but a brake fluid flush can be very advantageous.

Think about it this way: you meticulously maintain all the parts that make your 150mph motorcycle go, but how many things have you done to make sure that it stops? Flushing and bleeding your brakes will relieve some of the friction in the master cylinder and calipers, it can make the braking action feel more responsive and it'll give you confidence behind the bars. This is a simple process that you can do at home with basic tools.

Assuming that you're not very good at this mechanic stuff, aside from knowing terminology which is onlya short Google search away, maintenance is about as difficult as piecing together a simple Lego set. It just takes patenience and reading.

Requirements

Certain bikes vary, but the majority of motorcycles require these items for a flush:
- Oily rags and container
- Translucent tubing that fits over the bleed valves
- An 8mm open end wrench (or a 5/16 because your irresponsible brother lost your 8mm)
- Brake fluid (check owner’s manual for type).

bleed valve

Step 1: Rags, plenty of them

Put some rags under the brake fluid reservoir, calipers and any other obvious splash zones. You ARE going to spill brake fluid, no matter how carefully you work, so be generous with the rags.

Step 2: Drain hose

Slip one end of the tubing over the nipple of the bleed valve and insert the other end in a container. Crack open the bleed valve and repeatedly pump your brake lever until the fluid exiting the valve is mostly air. If you have two front brake calipers like I do on my Triumph Speed Triple, close off the first side and repeat the process with the other.

Bleed setup

Step 3: Pump and release

A motorcycle’s braking system works very similar to the way the pump on a blood pressure cuff does. To bleed the air from your brake lines, optimistically fill the fluid reservoir, open the bleed valve, slowly squeeze and hold the brake lever, close the bleed valve, and slowly let go of the brake lever. Repeat this about six hundred times, making sure to keep fluid in the reservoir (if air gets sucked into the master cylinder, you will have to repeat the entire bleeding process). When the bubbles become less frequent, move to the other caliper. Bleed this one until there are absolutely no bubbles coming from the bleed valve, and then go back to the first caliper to finish the job.

Poke two small holes into the foil seal for better precision.
Poke two small holes into the foil seal for better precision.

Most service manuals suggest to bleed the first caliper until there are no bubbles coming from the bleed valve, and to repeat with the second caliper, but I've never been able to fully bleed the first caliper without fluid in the other line, which is why I suggest to finish with the first caliper, before moving on.

Bubble demo

Step 4: Top off

When your brake system has been properly bled, the brake lever action should feel firm. Fill the fluid reservoir to the “upper” level indication. Replace the reservoir’s cap and diaphragm, removing any dust it may have collected.

Using the same procedure as above, flush the rear braking system. To put your mind at ease, make sure all of the bleed valves and reservoir caps are tightened and op-test the brakes. Now that you've finished the flush, clean and stow your tools and ride up to the clouds.

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