Figure 12-23.-Goodyear master brake cylinder.
Goodyear Master Cylinder
A cutaway view of the Goodyear master cylinder is
shown in figure 12-23. Fluid is fed by gravity to the
master cylinder from an external reservoir. The fluid
enters through the cylinder inlet port and compensating
port and fills the master cylinder casting ahead of the
piston and the fluid line leading to the brake actuating
cylinder.
Application of the brake pedal, which is linked to
the master cylinder piston rod causes the piston rod to
push the piston forward inside the master cylinder
casting. A slight forward movement blocks the
compensating port, and the buildup of pressure begins.
This pressure is transmitted to the broke assembly.
When the brake pedal is released and returns to the
OFF position, the piston return spring pushes the front
piston seal and the piston back to full OFF position
against the piston return stop. This action again clears
the compensating port. Fluid that was moved into the
brake assembly and brake connecting line is then pushed
back to the master cylinder by the brake piston as the
piston is returned to the OFF position by the pressure of
the brake piston return springs.
Any pressure or excess volume of fluid is relieved
through the compensating port and passes back to the
fluid reservoir. The compensating port assures against
dragging or locked brakes.
If any fluid is lost back of the front piston seal due
to leakage, it is automatically replaced with fluid from
the reservoir by gravity. Any fluid lost in front of the
piston from leaks in the line or at the brake is
automatically replaced through the piston head ports,
and around the lip of the front piston seal when the piston
makes the return stroke to the full OFF position. The
front piston seal functions as a seal only during the
forward stroke. These automatic fluid replacement
arrangements always keep the master cylinder, brake
connecting line, and brake assembly fully supplied with
fluid as long as there is fluid in the reservoir.
The rear piston seal seals the rear end of the cylinder
at all times to prevent leakage of fluid. The flexible
rubber boot serves only to keep out dust.
Provision is made for locking the brakes for parking
by a ratchet-type lock built into the mechanical linkage
between the master cylinder and the brake pedal. Any
change in the volume of fluid, due to expansion while
the parking brake is on, is taken care of by a spring
incorporated in the linkage. The brakes are unlocked by
application of sufficient pressure on the brake pedals to
unload the ratchet.
Brake systems employing the Goodyear master
cylinder must be bled from the top down. In no case
should bleeding be attempted from the bottom up,
because it is impossible to remove the air in back of the
piston seal. Bleeding operations are covered later in this
chapter.
Gladden Master Cylinder
The Gladden master brake cylinder consists of a
cylinder body, valve, piston, piston rod, return springs,
and a stop assembly, as shown in figure 12-24. The
piston rod extends through the valve, the piston, the stop
assembly, and the return springs, and is connected by an
eyebolt to the broke arm on the rudder pedal.
When the cylinder is in neutral, the valve is not
seated. Fluid from an independent brake reservoir enters
the cylinder’s reservoir port. Fluid entering this port is
allowed to flow through the piston and fill the lower
chamber.
When the rudder pedal is depressed by toe pressure,
the piston rod is pulled downward, causing the valve to
seat and close the piston orifice, This movement also
forces fluid into the brake’s pressure line to the wheel
brake assembly, thus applying the brakes.
12-30
