Chevrolet Cobalt Service & Repair Manual: Description
Front & Rear Split System
| When the brake pedal is depressed,
both the primary (front brake) and the secondary (rear brake) master cylinder
pistons are moved simultaneously to exert hydraulic fluid pressure on their
respective systems. |
| If the rear brake system fails,
initial brake pedal movement will cause the unrestricted secondary piston
to bottom in the master cylinder bore. Primary piston movement will displace
hydraulic fluid in the primary section of the master cylinder to actuate
the front brake system. |
| If the front brake system fails,
initial brake pedal movement will cause the unrestricted primary piston
to bottom out against the secondary piston. Continued downward movement
of the brake pedal moves the secondary piston to displace hydraulic fluid
in the rear brake system to actuate the rear brakes. |
Diagonally Split System
| This system operates on the same
principle as conventional front and rear split systems, using primary and
secondary master cylinders which move simultaneously to exert hydraulic
pressure on their respective systems. The hydraulic brake lines on this
system, however, have been diagonally split front to rear (lefthand front
to righthand rear and righthand front to lefthand rear) in place of separate
lines to the front and rear wheels. |
| In the event of a system failure,
the remaining non-failed system will do all the braking on one front wheel
and one rear wheel, maintaining 50% of the total braking force. |
Components
Warning Lamp
| The warning lamp should illuminate
when the ignition switch is in the start position and turn off when the
switch returns to run. If the brake lamp remains on after the ignition returns
to run, inspect fluid level in master cylinder reservoir and inspect parking
brake. If the warning lamp does not turn on during cranking, inspect for
faulty bulb or blown fuse. |
Fluid Level Sensor
| This sensor, mounted on the master
cylinder, will activate the brake warning lamp if a low brake fluid level
is detected. The lamp will turn off once the fluid level is corrected. |
Brake Warning Lamp Switches
| As pressure falls in one system,
the other system's normal pressure forces the piston to the inoperative
side, contacting the switch terminal, causing the warning lamp on the instrument
panel to glow. |
| The switch is mounted directly
in the master cylinder assembly. Whenever there is a specified differential
pressure, the switch piston will activate the brake failure warning switch
and cause the brake warning lamp to glow. |
Combination Valve
| The combination valve is a metering
valve, failure warning switch, and a proportioning valve in one assembly
and is used on disc brake applications. The metering valve delays front
disc braking until the rear drum brake shoes contact the drum. The failure
warning switch is actuated in event of front or rear brake system failure,
in turn activating a dash warning lamp. The proportioning valve balances
front to rear braking action during rapid deceleration. |
Metering Valve
| When the brakes are not applied,
the metering valve permits the brake fluid to flow through the valve allowing
the fluid to expand and contract with temperature changes. |
| When the brakes are initially
applied, the metering valve stem moves to the left, preventing fluid to
flow through the valve to the front disc brakes. This is accomplished by
the smooth end of the metering valve stem contacting the metering valve
seal lip at 4-30 psi. The metering valve spring holds the retainer against
the seal until a predetermined pressure is produced at the valve inlet port
which overcomes the spring pressure and permits hydraulic pressure to actuate
the front disc brakes. The increased pressure into the valve is metered
through the valve seal, to the front disc brakes, producing an increased
force on the diaphragm. The diaphragm then pulls the pin, in turn pulling
the retainer, and reduces the spring pressure on the metering valve seal.
Eventually, the pressure reaches a point at which the spring is pulled away
by the diaphragm pin and retainer, leaving the metering valve unrestricted,
permitting full pressure to pass through the metering valve. |
Failure Warning Switch
| If the rear brake system fails,
the front system pressure forces the switch piston to the right. The switch
pin is then forced up into the switch, completing the electrical circuit
and activates the dash warning lamp. |
| When repairs are made and pressure
returns to the system, the piston moves to the left, resetting the switch.
The detent on the piston requires approximately 100-450 psi to permit full
reset of the piston. In event of front brake system failure, the piston
moves to the left and the same sequence of events is followed as for rear
system failure except the piston resets to the right. |
Proportioning Or Pressure Control Valve
| During rapid deceleration, a portion
of vehicle weight is transferred to the front wheels. This resultant loss
of weight at rear wheels must be compensated for to avoid early rear wheel
skid. The proportioning or pressure control valve reduces rear brake system
pressure, delaying rear wheel skid. When the proportioning or pressure control
valve is incorporated in the combination valve assembly, pressure developed
within the valve acts against the large end of the piston, overcoming the
spring pressure, moving the piston left. The piston then contacts the stem
seat and restricts line pressure through the valve. |
| During normal braking operation,
the proportioning or pressure control valve is not functional. Brake fluid
flows into the proportioning or pressure control valve between the piston
center hole and the valve stem, through the stop plate and to the rear brakes.
Spring pressure loads the piston during normal braking, causing it to rest
against the stop plate. |
| On diagonally split brake systems,
two proportioning or pressure control valves are used. One controls the
lefthand rear brake, the other the righthand rear brake. The proportioning
or pressure control valves are installed in the master cylinder rear brake
outlet ports. |
Brake Distribution Valve & Switch
| This switch assembly is used on
some diagonally split brake systems and Corvette four-wheel disc brake systems.
It is connected to the outlet ports of the master cylinder and to the brake
warning lamp and warns the driver if either the primary or secondary brake
system has failed. |
| When hydraulic pressure is equal
in both primary and secondary brake systems, the switch remains centered.
If pressure fails in one of the systems, the piston moves toward the inoperative
side. The shoulder of the piston contacts the switch terminal, providing
a ground and lighting the warning lamp. |
Master Cylinder Overhaul
Impala
Disassemble
Refer to Figs. 1
and 2, when performing the following procedures.
1.
Disconnect and plug hydraulic lines.
...
Year
Component
Torque Ft. Lbs.
AVEO
2010
Bleeder Screw
80 1
Bleeder Va ...
Chevrolet Cobalt Owners Manual
Chevrolet Cobalt Service Manual
Component Service
Tightening Specifications