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Brakes air bleeding

This page summarizes two different operations :

Be careful, if there is really a lot of air in circuit, it mght last very very (very ;-) ) long. Take new brake fluid, and open the filler cap of the master cylinder. Protect all parts around because brake fluid is very corrosive for paintings and plastics. You will have to install your 'bleeding tool' on the brake. Find the bleed valve.

Vis de purge

Install a transparent hose on it (this transparent pipe may help you to see how much air is escaping the brake).

Tuyau transparent sur la vis de purge

This pipe goes in a jar. Everyone may have its own technic to do clean job (I mean without brake fluid everywhere on the ground). Here is mine !

Bocal réceptionnant le liquide usagé

If you replace brake fluid, use the syringe to remove the old one in the master cylinder, and fill it with new one. If just want to bleed air, don't do anything.

Remplissage du bocal à la seringue

Here begins the real bleeding action. The idea is to replace step by step the brake fluid which is in the circuit and to remove air in the same time. Here is the process, and it could be easier if you had a friend to help you.

And do it again ! On some bikes with complex brake circuits (like dual CBS), there is a special procedure. Check your service manual for more informations.

And there is another trap which can make you see air escape without ending. If the bleeding pipe is full, it can create a depression at the bleed valve. There is still a few air that might go beetween screw and brake body into your transparent hose. You think that this air was in circuit, and you keep bleeding....

Once brake is hard enough (and brake fluid which escapes is clean if you were replacing it), tighten bleed valve, adjust level in master cylinder, and check for the last time there is no fluid on the plastic and painted parts around.