Lesson 1/Learning Event 2
FIGURE 11. MASTER CYLINDER.
The master cylinder housing is an iron casting which contains the
cylinder and a large reservoir for the brake fluid. The reservoir
carries enough reserve fluid to ensure proper operation of the
braking system. It is filled through a hole at the top which is
sealed by a removable filler cap containing a vent. The cylinder is
connected to the reservoir by two drilled holes or ports, a large
intake port, and a small bypass port.
The master cylinder piston is a long, spoollike member with a rubber
secondary cup seal at the outer end and a rubber primary cup which
acts against the brake liquid just ahead of the inner end. The
primary cup is kept against the end of the piston by a return spring.
The inner piston head has several small bleeder ports that pass
through the head to the base of the rubber primary cup. A steel stop
disk, held in the outer end of the cylinder by a retaining spring
(snap ring), acts as a piston stop. A rubber boot covers the piston
end of the master cylinder to prevent dust and other foreign matter
from entering the cylinder. This boot is vented to prevent air from
being compressed within it.
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