Dodge ram truck 3500 1996 Service Manual page 187

SBF1
BRAKES 5 - 3
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RED BRAKE WARNING LA1P
A red warning lamp is used for the service brake
portion of the hydraulic system. The lamp is located
in the instrument panel.
The red warning light alerts the driver i f a pres­
sure differential exists between the front and rear
hydraulic systems. The light also alerts the driver
when the parking brakes are applied.
Power Brake Booster
All BR models are equipped with a tandem (dual)
diaphragm power brake booster (Fig. 2). Two versions
are used. A standard duty is used in all 1/2 ton mod­
els and a higher output version Is used in 3/4 and 1
ton models. The standard and high output boosters
are identified by code letters on the forward face of
the booster (Fig. 2).
Booster I.D. code letters are as follows:
• 1/2 ton booster code: ZK
• 3/4 and 1 ton booster code: ZL
The only serviceable power brake booster compo­
nents are the vacuum hose and check valve. The
booster itself is not a repairable component. The
booster must be replaced as an assembly whenever
diagnosis indicates a fault has occurred.
POWER BRAKE BOOSTER OPERATION
The booster assembly consists of a housing divided
into separate chambers by two internal diaphragms.
The outer edge of each diaphragm is attached to the
booster housing. The diaphragms are in turn, con­
nected to the booster push rod.
Two push rods are used to operate the booster. One
push rod connects the booster to the brake pedal. The
second push rod (at the forward end of the housing),
strokes the master cylinder pistons. The rear push
rod is connected to the two diaphragms in the
booster housing.
The atmospheric Inlet valve is opened and closed
by the push rod connected to the brake pedal. The
booster vacuum supply is through a hose attached to
a fitting on the intake manifold. The hose is con­
nected to a vacuum check valve in the booster hous­
ing. The check valve is a one-way device that
prevents vacuum leak back.
Power assist is generated by utilizing the pressure
differential between normal atmospheric pressure
and a vacuum. The vacuum needed for booster oper­
ation is taken directly from the engine intake mani­
fold. The entry point for atmospheric pressure is
through an inlet valve at the rear of the housing.
The forward portion of the booster housing (area in
front of the two diaphragms), is exposed to manifold
IDENTIFICATION
CODE
LOCATION
CHECK
VALVE
MASTER
CYLINDER
MOUNTING
STUDS
BOOSTER
PUSH ROD
(TO MASTER
CYLINDER)
INTEGRAL
MOUNTING
BRACKET
BOOSTER
PUSH ROD
(TO BRAKE
PEDAL)
BOOSTER
MOUNTING
STUDS
FRONT VIEW SIDE VIEW REAR VIEW
J9405-20
Fig. 2 Power Brake Booster