S1 Publishing(Oxford)© 2005-06

World of motorcycleS
S1 Publishing(Oxford)© 2005-06
Disc Brakes
How it works and why bleeding is neccessary sometimes.
The braking system is quite siple, as you pull on the brake, the piston (in red) forces the brake fluid (in yellow) through the tube, this pushes the piston(s) in the caliper onto the  brake pad against the disc.

If air & or water gets into the system the air or water in the tube gets compressed instead of pushing the piston, this leads to either poor brakes or worse, total loss of brakes


Bleeding, the basics.....

Here is one of the most complicated braking systems you will come across, comprising of 6 bleed nipples!
It has a twin disc set up, and anti dave system.
For twin brake systems always start with the shortest hose first 

On this machine (Kawasaki GPZ 1000RX) it would be right fork, splitter bleed nipple where there are three hoses joining into a single banjo

then anti-dive nipple

then caliper nipple.
Then the same on the front left side of the system
1. Locate the master cylinder, on the front brake, usually found on the right handlebar, for the rear, it's usually found near, under the side panel, or the swinging arm. Wrap a cloth under the cylinder to stop spilt fluid getting onto any paint work, as brake fluid is a very good paint stripper. Then undo the top of the cylinder, this will have a screw top (e.g.. old Honda cb750s), or a few screws. 
Remove the rubber, then top up with the recommended brake fluid (usually DOT4) 
Note, do not let the resevoir run out of fluid, if this happens, you will have to start again as air will be sucked into the system

2.  Place the spanner onto the bleed nipple. Then place a clear tube over the nipple and place the other end of it into a bottle. This will show any air bubbles that might have got into the system, as well as stopping any splis of brake fluid or air getting back into the system during bleeding.
3. Undo the Bleed nipple a quarter turn.  
4. Then pull the brake lever, to push fluid through the system, and keep it full on.
 Releasing the lever before closing the bleed nipple will allow air to get into your system!
 5. Do up the bleed nipple. 
6 Release the brake lever. Repeat this steps 3 to 6, topping up the cylinder with fluid as necessary. When you can see no air bubbles coming through the tube. the system is bled.

7. When the fluid is between the levels marked, replace the top, then clean all spilt fluid, from both the cylinder and the caliper.
8. Hold the brake lever on and try to move the bike, just to make sure that the brake is working BEFORE RIDING! 
Note. Bleed nipples are notorious for seizing, It is a good idea to use a penetrating oil before trying to undo them. In severe cases you might even have to heat the caliper and nipple using a blowtorch. If this is the case, make sure not to burn any of the rubbers. If the nipple snaps, then if you are very careful you might be able to drill it out, taking care not to damage the thread, if you damage the thread then you might be able to re-tap it and use a over-sized nipple, as a last resort..... replace the caliper! 

I reccommend replacing all bleed nipples after 5-7yrs or sooner.

Another reason brakes can loose efficiency, or fail...
If the brake hoses are too old, they can perish
I use Goodrich Braided hoses on all my hydraulic systems, which eliminates such problems!

 Check the brake pads, these can usualy been seen in the gap between the disc (rotor) and the caliper.
 There are a few types of types of fixings for pads, I'll try to show the different types soon.
I use EBC Sintered pads on mine

Under contruction!
Sticking pads, caliper seals replacement and caliper renervation to follow

This is just a general guide.
If you are about to do your own maintenance, using these pages, I take no responsibility if you get things wrong!
Last updated 06-09-08