Tutorial to Bleed Motorbike Brakes
The first time I decided to strip down the front brakes on my Honda Superdream, I thought it best to follow the manual. I duly bought one on ebay and then set about following the instructions as carefully as possible. All well and good, the manual was from a reputable company (famous in the UK for strip-downs of any vehicle you could mention) and most of what it said was accurate and helpful. However, when it came to bleeding the brakes I found that the information given was hopeless.
In fact the method they suggested was in line with most other manuals and is considered by many to be the only way to bleed brake lines of air. That said, I couldn’t get it to work! So you can see what I am referring to I will quote
‘Check the level of the reservoir, and fill almost to the top. Place a jar below the brake caliper unit and attach a clear plastic tube from the calliper bleed screw to the container so that the pipe is always immersed below the surface of the fluid. Unscrew the bleed screw one complete turn and pump the handlebars lever slowly. As the fluid is ejected from the bleed screw the level in the reservoir will fall. Continue the pumping action with the lever until no further air bubbles emerge from the end of the pipe.’
I won’t quote any further as it was at this point that I discovered that the fluid just did not appear to flow out of the bleed nipple in the way it describes above. The Handlebar lever continued to be spongy and I eventually decided after slowly pumping for at least 20 minutes to think of another way to clear the air from the system.
One of the key problems with motor bikes is that the brake lever is set right up on the handle bars, way above the caliper unit; unlike on a car where the pedal is on the floor, at more or less the same level as the calipers. This means that you are trying to force air down the brake lines, when all air wants to do is rise to the top (as it is lighter than the fluid of course). A solution might be to remove the lever and master cylinder from the handlebars and to pump the lever from a much lower position, as close to the level of the calliper as possible. I tried this, but because I’d had to remove the cover from the reservior to top up the liquid I managed to spill the fluid all over the place. Not ideal, as brake fluid works as a great paint stripper!
So now to my successful method! Rather than taking the reservoir off the handlebars, I instead undid the two bolts that secure the calliper to the fork. Next I slid the caliper unit away from the wheel. At this point you will probably find that your bike differs in someway from the Superdream, however you should find that it’s possible to place a G-clamp (screw end) into the calliper piston. This will only be possible if you remove the brake pads and any retaining pins etc. You may also find that there are various protective rubber skirts etc. around the piston itself. This shouldn’t be a problem as long as you don’t snag these in the clamp as you turn the screw.
With the pads out of the way, I pumped the handlebar lever a few times and forced the piston much further out of the calliper unit than it would normally be able to go. VERY IMPORTANT – DO NOT do this bit with too much enthusiasm and spring the piston right out of the calliper unit (unless you intend to do a full strip down and want to replace the piston seals). This will be very, very messy and getting the piston back into the unit will be harder than you think!
Next, I positioned the G-Clamp (screw end) over the piston and slowly turned it until it reached the base of the piston.
Before continuing I removed the cover from the reservoir on the handlebars and then as I turned the screw I watched the air from the brake line bubble its way to the top of the reservoir. Eventually the bubbles stopped appearing and I knew that there air had all been forced out of the system. The piston was back in its original position and the brake pads could be pushed back into place, secured and the whole unit bolted back onto the fork.
Yes, it was a little more complicated than conventional bleeding; but, it was cleaner; no nipples to undo, no plastic pipes held under the surface of the ejected fluid, in fact, no fluid at all had to be ejected from the system. I didn’t have to pump away at the lever for ages, waiting for a sign of success. The G-Clamp did it all.
At this point I can see that simple instructions without the story might be appropriate, so here is the simple version. 1. Undo the bolts that secure the calliper unit to the forks. 2. Slide calliper unit away from the wheel. 3. Remove brake pads and retaining pins etc. 4. Pump the handlebar lever slowly until the piston has been pushed quite a way out of the unit (a couple of centimetres max.) 5. Slot a G-Clamp over the calliper unit and position the screw end over the piston. 6. Screw down until screw end makes contact with the base of the piston. 7. Remove cover from reservoir on the handlebars. 8. Continue screwing G-Clamp and watch the little air bubbles rising to the top of the reservoir. 9. When there are no more air bubbles and the piston is right back where it started your job is done. 10.Replace cover of reservoir; slide brake pads back into place and replace retaining pins; secure calliper unit back onto fork.
At this point I must add that I am not a mechanic and I only mess about with bikes and cars for fun. However, having used this method I took the bike for its annual MOT (Ministry of Transport) Test, and it passed with flying colours. Brakes super efficient and safe for the road.
About the Author
I work on bikes and cars for fun and I am not a professional mechanic, but I have spent many hours on my own machines and know every inch of them by the time I’m done. I am also an artist and have articles on painting and printmaking to submit in the future.
Tags: Bleed Motorbike Brakes