Dodge RAM TRUCK 1500 1995 Service Manual page 189

B R
POWER BRAKE BOOSTER—BRAKE PEDAL—BRAKELIGHT SWITCH 5-17
PEDAL SHAFT
Fig. 2 Suspended Style Brake Pedal
Fig. 3 Brakelight Switch Location And Mounting
POWER BRAKE BOOSTER SERf ICEABiLITY
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
Booster Components
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 connected to a vacuum
check valve in the booster housing. The check valve is a
one-way device that prevents vacuum leak back.
How Brake Boost Is Generated
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
vacuum. The rear portion (area behind the dia­
phragms), is exposed to normal atmospheric pressure
of 101.3 kilopascals (14.7 pounds/square in.).
Pressing the brake pedal causes the rear push rod
to open the inlet valve. This exposes the area behind
the diaphragms to atmospheric pressure. The result­
ing force applied to the diaphragms is what provides
the extra boost in apply pressure for power assist.
POWER BRAKE BOOSTER REMOVAL
(1) Disconnect harness wires from differential
switch on combination valve and from RWAL valve.
(2) Disconnect brakeline from combination valve to
front brakes, or ABS valve. Then disconnect brake-
line from RWAL valve to rear brakes.
(3) Remove nuts attaching master cylinder and
valves to power brake booster studs. Then remove
master cylinder and valves as assembly (Fig. 4).
Fig. 4 Removing/Installing Master Cylinder And
Valves As Assembly