How To Bleed Them
Basically there are 3 reasons why you want to bleed your motorcycle brakes:
- After a big tumble the brake feels spongy and weak
- You replaced the master cylinder kit
- Your manual recommends that you replace brake fluid
My bike is upside down in regular intervals. So on more than one
occasion I had the pleasure to find out the following: if the brake
lever has been accidentally pulled in while the bike is restored to its
normal rubber-side-down stance, the brake can feel spongy and weak.
bubble of air has been introduced to the system. For a hydraulic brake
system to work properly, all air must be removed and this process is
called bleeding the motorcycle brakes.
What you will need
- Usual hand tools
- Catch bottle
- Fluid specified in your manual
- Clean environment
yourself a piece of plastic pipe that fits exactly over the bleed
nipple in the calliper. Then bore a hole in the cap of an old oil bottle
and push the other end of the pipe through that.
fluid strips paint very efficiently! If you do happen so spill some on a
painted surface, wipe it off immediately and flush the area with hot
Only use the brake fluid specified in your manual or embossed on the reservoir cap of the master cylinder.
WORKING ON BRAKES
Absolute cleanliness is important when working around motorcycle brakes. Make sure no dirt can fall into the fluid reservoir.
double and triple check everything. A flailed motorcycle brake can put
you into hospital quicker than you can blink! (Thanks Andy for testing
that for us!)
The rear brake is easiest to do. So let's start with this one
a ring spanner of the correct size over the nipple and check that the
nipple can be opened and closed. If it is seized, take it to your dealer
and let them sort it out.
- Fit the nipple end of your catch bottle onto the nipple
the reservoir top of the master cylinder which will either be a big
nut, or a cap secured by two Philips head screws. If the screws are
reluctant to budge, seat the screwdriver into its slot, then tap the end
of the screwdriver with a hammer.
- Check that the reservoir is full of fluid, topping up if necessary.
- Put a cloth between the brake lever and your hand and pump the brake lever up and down about 5 times.
- Holding the brake lever down, open the nipple with the spanner in your other hand, then close it again.
- Repeat this whole operation about five times
- Check the level of fluid in the reservoir, topping up when necessary. Continue until brake lever has good solid feel.
push brake pedal down for about 1 min. Make sure it does not move. If
it moves down slowly under pressure it means that either the rubbers
inside the master cylinder are worn or that there is leak at one of the
fitting at either end of the brake pipe.
- When you are happy close up the reservoir, ensuring that the expansion rubber is clean and pressed right back.
the catch bottle and replace the rubber protector over the nipple.
Clean up any brake fluid that may have got onto the disc or pads.
Exactly the same procedure is followed with some small differences:
- You may have to loosen the throttle housing for clear access to the reservoir.
- To get one hand onto the brake lever and one hand on the bleed nipple spanner will be more difficult.
- There is more volume of fluid so it will take longer.
are some front brakes that will just never bleed up properly. This is
quite common on Brembo set-ups, less so on Nissin equipment
If your motorcycle brake is not coming right, read on before you lose your temper...
When a brake won't bleed up
When motorcycle brakes won't bleed, a bubble of air is moving down the
brake pipe when you release the pressure at the nipple.
When you tighten
up the bubble moves back up the pipe a bit and so never gets close to
the nipple where it can be expelled from the system.
If you ask for advice on this problem people will tell you to reverse
bleed by squirting brake fluid into the nipple with a syringe. This
doesn't seem to work very well either.
So here is what Andy (my favourite mechanic suggests):
brake nipple has to be the highest part of the system, so remove the
calliper, brake pipe and master cylinder from the bike as a complete
- Using a trestle or something similar, clamp the master cylinder to a low point on your rig.
- With a "G" clamp, clamp the calliper to the top of the rig with the bleed nipple uppermost.
Between the brake pads, slide a piece of wood or metal approximately
the same thickness as the brake disc. If you don't do this you run the
risk of popping the brake pistons right out of the calliper
- Make sure that no part of the brake pipe is higher than the bleed nipple and start your pumping and opening and closing routine.
The brake should come right very quickly. If it doesn't, you have master cylinder rubber problems.
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