2-18 PERIODIC MAINTENANCE
AIR BLEEDING THE BRAKE FLUID CIRCUIT
Air trapped in the brake fluid circuit acts like a cushion to absorb
a large proportion of the pressure developed by the master cylin-
der and thus interferes with the full braking performance of the
brake caliper. The presence of air is indicated by “sponginess” of
the brake lever and also by lack of braking force. Considering the
danger to which such trapped air exposes the machine and rider,
it is essential that, after remounting the brake and restoring the
brake system to the normal condition, the brake fluid circuit be
purged of air in the following manner:
• Fill the master cylinder reservoir to the top of the inspection
window. Replace the reservoir cap to prevent dirt from enter-
ing.
• Attach a hose to the air bleeder valve, and insert the free end
of the hose into a receptacle.
• Front brake: Bleed air from the brake system.
• Squeeze and release the brake lever several times in rapid
succession and squeeze the lever fully without releasing it.
Loosen the air bleeder valve by turning it a quarter of a turn so
that the brake fluid runs into the receptacle, this will remove
the tension of the brake lever causing it to touch the handlebar
grip. Then, close the air bleeder valve, pump and squeeze the
lever, and open the valve. Repeat this process until the fluid
flowing into the receptacle no longer contains air bubbles.
NOTE:
While bleeding the brake system, replenish the brake fluid in the
reservoir as necessary. Make sure that there is always some fluid
visible in the reservoir.
• Close the air bleeder valve, and disconnect the hose. Fill the
reservoir with brake fluid to the top of the inspection window.
) Air bleeder valve: 8 N
.
m (0.8 kgf
.
m, 6.0 lb-ft)
'
Handle brake fluid with care: the fluid reacts chemically
with paint, plastics, rubber materials, etc.
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