Maintenance Article #1: How To Bleed Your Motorcycle Brake System

    Joe Denowh is not only a certified motorcycle mechanic who’s been riding and wrenching for his entire life, he’s also a Midwest regional club racing middleweight champion, and the Chief Service Technician for Turn One Racing. In this ongoing series of articles Joe will explain the right, and sometimes the wrong, way of how to maintain and modify your high performance motorcycle.

    The thing is most people overthink how to bleed brakes on a motorcycle. You don’t need a bunch of fancy tools, and it ain't rocket science, you just need a few basic tools and the patience and technique required to do the job right.

    Step 1: Gather your tools and materials. You’ll need a fresh bottle of high quality brake fluid preferably unopened, as brake fluid has an annoying tendency to suck moisture out of the air, and moisture is no good for brake fluid. You’ll also need some clear tubing, 1/4” to 3/8” in diameter, depending on your bleed valves. You want the tube to fit very tightly over the valve, so tight it doesn’t leak or pop off while you work. An 8mm open end wrench fits most bleeder valves. A few rags are always a good idea and will help keep evil brake fluid from eating your paint and plastics if you happen to spill any. Make sure you never spill any brake fluid on your brake pads once you contaminate the braking surface of your pad with fluid you’ll need to replace the pads, so take extra care not to spill any brake fluid on your pads or brake rotors.

    Lastly, you’ll need to find a nice heavy container to snake the hoses into that won’t tip over while you work. It’s a good idea to dedicate this as your brake bleeding catch bottle from now on.

    Step 2: Put yourself and your bike in a nice clean and dry area. There’s nothing worse than a dirty, wet environment for bleeding brakes. The last thing you want in your brake fluid reservoir is water or dirt. Even the smallest amount of either can affect the performance of your brakes.

TIP: If your master cylinder doesn’t have a bleed valve, or if you just want to save some time, use a vacuum or a pressure bleeder to move fluid through your brake system, but remember there’s no substitute for hand bleeding at the end, it’s the best way to get the system completely free from tiny air bubbles.

    Step 3: Put one end of your bleeder hose on your master cylinder bleed valve, if you have one, and the other end into the catch bottle. The hose should be hard to get on the bleed valve, if it goes on too easy it probably won’t stay on while you’re bleeding.

    Step 4: Take the top off your brake fluid reservoir, and have your bottle ready to add brake fluid as you bleed the contents of the reservoir down through your brake lines. Now is a good time to lay a rag around the area to protect your bike from any spills.

    Step 5: With one hand on the brake lever and one hand on the open end wrench now it’s time to begin bleeding your brakes. Make sure to keep an eye on your reservoir so you DON’T ALLOW THE FLUID IN THE RESERVOIR TO COMPLETELY RUN OUT. The idea is to only bleed the fluid down to the bottom of the reservoir and then add more fresh fluid, repeating the process until all the bubbles are out of your system.

    Bleed Sequence: With one hand, pump the brake lever two or three times to build pressure, then hold the lever in under pressure. With the other hand on the wrench, slowly open the bleed valve so fluid moves into the clear plastic hose.

    As fluid moves into the hose, the lever will come back to the bar, DON’T RELEASE THE LEVER UNTIL AFTER YOU CLOSE THE BLEED VALVE. With the valve is closed, you can pump the lever again to build pressure. Once you have pressure at the lever again, hold it there while you slowly open the bleed valve again to release air and move fluid, as the lever returns to the handle bar, HOLD IT THERE WHILE YOU CLOSE THE BLEED VALVE again, now you can pump the lever to build pressure and repeat the process until all bubbles are gone and you see no bubbles of any kind for at least three cycles of pumping and bleeding.

    Remember, bleed valves have very low torque settings, which means you don’t have to crank the living hell out of them to close them. There’s a tiny valve in there and you don’t want to crush it, so be firm, but gentle. Check your service manual for the exact torque value, but think tiny little soft bolt, not big, steel head torque, if you know what I mean.

    Step 6: Once you have clear fluid moving through the first bleed valve, carefully remove the hose from the valve so as not to spill or splatter any fluid. A rag in your hand as you cover the end of the hose and bleed valve while you remove it is a good idea. Then move on to the next bleed valve and repeat the entire process until only clear fluid passes through the hose.

    If you want, you can even run three separate hoses into the catch bottle so you don’t have to keep moving the same hose around the bike, but you really only need one.

    Always keep one eye on the master cylinder reservoir and add fluid every time it gets low. If you forget to do this and hear that awful sucking sound as air begins being sucked into the empty reservoir, prepare yourself for a long night!

    Once you have established that each of your bleed valves now moves only pure brake fluid from the master cylinder, you’re ready to top off the reservoir and close the system. DO NOT OVERFILL YOUR RESERVOIR, a common mistake many people make is to fill the reservoir all the way to the rim, but when your brakes get hot under heavy braking the fluid expands, and then seeps through the plastic threads and down around your master cylinder, which is one reason why factory teams use those little sweatbands around the master cylinder reservoir to absorb any excess fluid that may seep out under heat and pressure.

    One more thing to consider for racers and track riders is that the best way to absolutely guarantee the best in braking performance is to do what we call a “Hot bleed” at the track. This is when you have your brake bleeding operation ready to go in your pits so that when you come straight off the track you can bleed the brakes while the system is still hot and even the tiniest microbubbles can’t hide.

    Lastly, never forget FRESHER IS FASTER and that means brake fluid, brake pads, and everything else to do with going fast, including the rider. Nothing hurts us more than seeing someone with syrupy black goo in their brake reservoir, and tired old glazed brake pads on their bike. Keep your fluid fresh and properly bled, always use fresh high quality brake pads, and make sure you’re as well rested and well hydrated as you can be to guarantee the best performance from your motorcycle and yourself.

    Tune in again for another article on motorcycle maintenance, modification, and repair, because Joe Knows How To get the most out of your motorcycle experience.