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5 - 2
BRAKES
DESCRIPTION AND OPERATION
BASE BRAKE SYSTEM OPERATION
When a vehicle needs to be stopped, the driver
applies the brake pedal. The brake pedal pushes the
input rod of the power brake booster into the booster.
The booster uses vacuum to ease pedal effort as force
is transferred through the booster to the master cyl-
inder. The booster's output rod pushes in the master
cylinder's primary and secondary pistons applying
hydraulic pressure through the chassis brake tubes
and proportioning valves to the brakes at each tire
and wheel assembly.
Front disc brakes control the braking of the front
wheels; rear braking is controlled by rear drum
brakes as standard equipment. Rear disc brakes are
optional.
The hydraulic brake system is diagonally split on
both the non-antilock and antilock braking systems.
This means the left front and right rear brakes are
on one hydraulic circuit and the right front and left
rear are on the other.
Vehicles equipped with the optional antilock brake
system (ABS) use a system designated Mark 20,
which is supplied by ITT Teves. This system shares
most base brake hardware used on vehicles without
ABS. A vehicle equipped with ABS, however, uses a
different power brake booster, master cylinder, and
brake tubes. Also included in the ABS system is an
integrated control unit (ICU), four wheel speed sen-
sors, and an electronic controller referred to as the
controller antilock brake (CAB). These components
are described in detail in the ANTILOCK BRAKE
SYSTEM section in this group of the service manual.
The parking brakes are hand-operated. When
applied, the parking brake lever pulls on cables that
actuate brake shoes at each rear wheel. The parking
brake lever has an automatic adjusting feature that
takes up any excessive slack in the parking brake
system.
MASTER CYLINDER
This vehicle uses 2 differently designed master cyl-
inder assemblies depending on whether the vehicle is
or is not equipped with antilock brakes.
Vehicles not equipped with ABS use a standard
compensating port master cylinder design, while
vehicles equipped with ABS use a center valve design
master cylinder.
On vehicles equipped with ABS brakes, the master
cylinder is a two outlet design. On vehicles not
equipped with ABS brakes, the master cylinder is a 4
outlet design. All vehicles are equipped with a mas-
ter cylinder having a bore diameter of 22.2 mm.
The master cylinder assembly (Fig. 1) consists of
the following components. The body of the master
cylinder is an anodized aluminum casting. It has a
machined bore to accept the master cylinder piston
and threaded ports with seats for hydraulic brake
line connections. The brake fluid reservoir of the
master cylinder assembly is made of a see through
polypropelene type plastic.
Fig. 1 Master Cylinder
On Non-ABS master cylinders, the primary outlet
ports (Fig. 2) supply hydraulic pressure to the right
front and left rear brakes. The secondary outlet ports
(Fig. 2) supply hydraulic pressure to the left front
and right rear brakes.
Fig. 2 Primary And Secondary Ports Without ABS
On ABS master cylinders, the primary outlet port
(Fig. 3) supplies hydraulic pressure to the right front
and left rear brakes. The secondary outlet port (Fig.
3) supplies hydraulic pressure to the left front and
right rear brakes.
POWER BRAKE BOOSTER
All vehicles use a 205 mm tandem diaphragm
power brake vacuum booster. The power brake vac-
uum booster though, may be unique for the type of
JA
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