Slave to Master Method - Bottom Up
Brake Bleeding
Brake bleeding is definitely a black art,
good results are often hard to achieve. This method explained
here may end your hours of misery trying in vain one more time
to get some resistance back into your master cylinder. But
there is no guarantee, all we can say is that it has worked for
us every time in the Trailtruck garage and takes no more than
20 minutes. It even gets a quick result if you have had to
drain all the fluid out and start with air in the whole system.
Basically this method injects the fluid from the caliper bleed
nipple and pushes the fluid and any trapped air up the system
to the reservoir.
Special tools required are one 60ml syringe and one 5ml syringe
and a short piece of clear tube. The tube must fit tightly
onto the end of the 60ml syringe and the other end tight onto
the bleed nipple. Also use clean brake fluid which has been
left to settle so there are no minute air bubbles in the fluid.
You will need another jar to dispose of the old fluid.
Start by setting the handle bar so the reservoir
is level and stable. Wedge the front wheel so it cannot move
and dislodge fluid. The brake lever must be held
away from the master cylinder so there is no contact with the
small piston; if in doubt remove the lever completely.
We wrap
paper rags around the master cylinder to catch any excess fluid
- brake fluid is very corrosive and can easily damage paint
and graphics, so protect your bike. It's also a good idea to
wrap a cover around your bar grips - later on, when you want
to pump the brakes, your hands may have oil or brake fluid
on them, so cover everything up before you start.
Remove the
reservoir cap and place on a clean cloth out of the way. Use
the 5ml syringe and suck out the fluid from the reservoir,
there will be about 10ml of fluid to extract. Dispose of the
fluid.
Attach the clear tube to the 60 ml syringe
and fill with about 50ml of new clean brake fluid. Invert the
syringe and push out the excess air so that the clear tube
is full to the end.
Position a ring spanner on your bleed nipple
(usually an 8mm).
Next carefully push the clear tube end onto
the bleed nipple, you
will see a small air bubble in the tube which is OK, don’t
try and get rid of it. Rest the tube in a vertical inclined
arc so that the small air bubble can rise up the tube away
from the nipple; it must be allowed to rise up about 25mm away
from the nipple.
You are now ready to start bleeding the system.
Maintain the tube in the inclined arc position and un screw
the bleed nipple about half a turn. Check the air bubble is
25mm away from the nipple. Note the ml reading on the syringe
plunger so you know how much fluid has been injected. Now start
injecting the fluid very, very slowly and keep an eye on the
bubble. It will move down toward the nipple and you must not
inject the bubble into the nipple, however as soon as you relax
the injection the bubble will rise back again. There will be
a substantial resistance as you inject. Do
not push too hard or you may damage the seals inside the system (read our top
tip on pressure within your brakes to learn more). Inject a
maximum of 10ml and then tighten the bleed nipple. The reservoir
will now be full of fluid and this must be removed with the
5ml syringe. Repeat the injection process again two more times,
but the final time only remove half of the fluid from the reservoir.
Leave the 60ml syringe on the bleed nipple.
Now is the moment of truth to see if you have
resistance to your brake lever. Refit the brake lever and pump
the brake; there should be resistance! If it feels spongy then
repeat the process a couple more times. The final step is now
to bleed in the conventional manner. With the syringe still
in place undo the bleed nipple just enough to allow the fluid
to escape and gently half pump the brake a dozen times in quick
succession and with the final pump pull the lever all the way
in and close the bleed nipple. You should now have a good solid
feeling brake system. Now replace the reservoir cap and check
the fluid level.
A final tip is to leave your bike overnight
with the brake lever pulled in. Provided the breather hole
in your reservoir is unblocked, any final air bubbles should
work their way up the system and vent to atmosphere. Simply
secure your brake lever in the on position with either a cable
tie, rubber bands, knicker elastic, tape, safety wire, small
child etc. what ever comes to hand!
If this method has not worked then it looks like the
black art has cast its shadow over your garage and you
are in for a long night of bleeding. Before you do that check
the system for damage and leaks at the hose joints.
Remember, old rubber brake hoses let moisture
through - if your brake fluid is old, or if you have left it
exposed to the atmosphere for any length of time, it will have
drawn moisture in and will not work as well.
DISCLAIMER! The
information offered here is an introduction to the
principles and parts of your motorcycle's braking system.
Reading this top tip will not turn you into an expert
brake mechanic! If after reading this page you feel
inclined to carry out alterations to the braking system
of your bike we will not accept responsibility for
what happens next! You are responsible for your own
actions and this page has been made available online
only to offer an introduction and to give you a greater
background understanding of how your braking system
works, what affects any changes you make may have and
what the different elements of the system do. If
you are in any doubt about the braking performance
or maintenance of your braking system consult your
local dealer.
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