Dodge ram truck 3500 1996 Service Manual page 255

BR
BRAKES I - 71
DESCRIPTION AND OPERATION
{Continued)
POWER
BRAKE
BOOSTER
FRONT
ANTILOCK
VALVE
RF
W H E E L
RR
W H E E L
LR
WHEEL
Fig. 1 ABS Hydraulic System
sensor signal indicate the onset of wheel lock-up the
ABS braking is activated.
The antilock system retards the lockup conditions
by modulating fluid apply pressure to the wheel
brake units. The pressure is modulated according to
wheel speed, degree of lock-up and rate of decelera­
tion.
The solenoid valves are cycled continuously to mod­
ulate pressure. Solenoid cycle time in antilock mode
can be measured in milliseconds.
CONTROLLER ANTILOCK BRAKES (CAB)
The CAB is located at the drivers inner fender
panel. The CAB is attached to the forward side of the
Hydraulic Control Unit mounting bracket (Fig. 2).
The CAB is used to monitor and operate the ABS
system. I t monitors the brake switch and wheel
speed sensors inputs to prepare for possible antilock
braking. The CAB controls the antilock valve sole­
noid operation during all phases of antilock braking.
HYDRAULIC CONTROL UNIT (HCU)
The HCU mounted on the driver side inner fender
panel (Fig. 2).
The HCU consist of the front antilock valve assem­
bly and pump/motor unit.
FRONT ANITLOCK VALVE
The front brake antilock valve consists of a sole­
noid valve body. The antilock valve provides two
channel pressure control of the front brakes. One
channel controls the left front brake unit. The second
HYDRAULIC
CONTROL UNIT
J9305-113
CONTROLLER
ANTILOCK B R A K E S
DRIVER
SIDE
FENDER
PANEL
RWAL
VALVE
80315898
Fig. 2 Controller Antilock Brakes and Hydraulic
Control Unit
channel controls the right front brake unit. Each
front brake unit is controlled independently.
The solenoid valves are cycled open and closed as
needed during antilock braking. They are cycled rap­
idly and continuously to modulate brake fluid pres­
sure and control wheel lock-up and deceleration.
PUMP/MOTOR
The pump is run by a DC type motor controlled by
the Controller Antilock Brake (CAB). The pump sup­
plies the additional fluid volume needed during
antilock braking.