Dodge Ram Truck 1500-2500-3500. Manual — part 215
The CAB monitors wheel speed sensor inputs continuously while the vehicle is in motion. However, the CAB will not
activate any ABS components as long as sensor inputs indicate normal braking.
During normal braking, the master cylinder, power booster and wheel brake units all function as they would in a
vehicle without ABS. The HCU components are not activated.
The purpose of the antilock system is to prevent wheel lockup. Preventing lockup helps maintain vehicle braking
action and steering control.
The antilock CAB activates the system whenever sensor signals indicate periods of wheel slip.
The antilock system prevents lockup during a wheel slip condition by modulating fluid apply pressure to the wheel
brake units.
Brake fluid apply pressure is modulated according to wheel speed, degree of slip and rate of deceleration. Sensors
at each front wheel convert wheel speed into electrical signals. These signals are transmitted to the CAB for pro-
cessing and determination of wheel slip and deceleration rate.
The ABS system has three fluid pressure control channels. The front brakes are controlled separately and the rear
brakes in tandem. A speed sensor input signal indicating a wheel slip condition activates the CAB antilock program.
There are Two solenoid valves (Isolation and Dump valve) which are used in each antilock control channel. The
valves are all located within the HCU valve body and work in pairs to either increase, hold, or decrease apply pres-
sure as needed in the individual control channels.
During an ABS stop the ISO valve is energized which acts to prevent further pressure build-up to the calipers. Then
the Dump valve dumps off pressure until the wheel unlocks. This will continue until the wheels quit slipping
altogether.
STANDARD PROCEDURE
ABS BRAKE BLEEDING
ABS system bleeding requires conventional bleeding methods plus use of the DRB scan tool. The procedure
involves performing a base brake bleeding, followed by use of the scan tool to cycle and bleed the HCU pump and
solenoids. A second base brake bleeding procedure is then required to remove any air remaining in the system.
1. Perform base brake bleeding, (Refer to 5 - BRAKES - STANDARD PROCEDURE) OR (Refer to 5 - BRAKES -
STANDARD PROCEDURE).
2. Connect scan tool to the Data Link Connector.
3. Select ANTILOCK BRAKES, followed by MISCELLANEOUS, then ABS BRAKES. Follow the instructions dis-
played. When scan tool displays TEST COMPLETE, disconnect scan tool and proceed.
4. Perform base brake bleeding a second time, (Refer to 5 - BRAKES - STANDARD PROCEDURE) OR (Refer to
5 - BRAKES - STANDARD PROCEDURE).
5. Top off master cylinder fluid level and verify proper brake operation before moving vehicle.
5 - 288
BRAKES - ABS - SERVICE INFORMATION
DR/DH
SPECIFICATIONS
TORQUE CHART
TORQUE SPECIFICATIONS
DESCRIPTION
N·m
Ft. Lbs.
In. Lbs.
ABS Assembly
Mounting Bolts
15
11
—
ABS Assembly
CAB Screws
3.5
—
31
ABS Assembly
Brake Line Fittings
19
—
170
Wheel Speed Sensors
Front Sensor Bolt
21
—
190
Wheel Speed Sensors
Bracket To Knuckle
6.7
—
60
Wheel Speed Sensors
Rear Sensor Stud
22.5
—
200
Controller
Mounting Screws
6
—
53
RWAL Module
Mounting Bolts
15
11
—
RWAL Valve
Brake Line Fittings
19
—
170
Rear Wheel Speed Sensor
Mounting Bolt
24
—
200
SENSOR- WHEEL SPEED-ABS-FRONT
DESCRIPTION
The ABS brake system uses 3 wheel speed sensors. A sensor is mounted to each front hub/bearings. The third
sensor is mounted on top of the rear axle differential housing.
OPERATION
The Wheel Speed Sensor consists of a magnet (1)
surrounded by windings from a single strand of wire
(5). The sensor sends a small AC signal to the ABM.
This signal is generated by magnetic induction. The
magnetic induction is created when a toothed sensor
ring (exciter ring or tone wheel) (4) passes the station-
ary magnetic WSS.
When the ring gear is rotated, the exciter ring (4)
passes the tip of the WSS. As the exciter ring tooth
approaches the tip of the WSS, the magnetic lines of
force expand, causing the magnetic field to cut across
the sensor’s windings (5). This, in turn causes current
to flow through the WSS circuit in one direction. When
the exciter ring tooth moves away from the sensor tip,
the magnetic lines of force collapse cutting the wind-
ing in the opposite direction. This causes the current
to flow in the opposite direction. Every time a tooth of
DR/DH
BRAKES - ABS - SERVICE INFORMATION
5 - 289
the exciter ring passes the tip of the WSS, an AC signal is generated current. Each AC signal (positive to negative
signal or squarewave) is interpreted by the ABM. It then compares the frequency of the sinewave to a time value to
calculate vehicle speed. The ABM continues to monitor the frequency to determine a deceleration rate that would
indicate a possible wheel-locking tendency.
The signal strength of any magnetic induction sensor is directly affected by:
•
Magnetic field strength; the stronger the magnetic field, the stronger the signal
•
Number of windings in the sensor; more windings provide a stronger signal
•
Exciter ring speed; the faster the exciter ring/tone wheel rotates, the stronger the signal will be
•
Distance (3) “air gap” between the exciter ring teeth and WSS; the closer the WSS is to the exciter ring/tone
wheel, the stronger the signal will be.
The WSS is not adjustable. A clearance specification has been established for manufacturing tolerances. If the
clearance is not within these specifications, then either the WSS or other components may be damaged. The clear-
ance between the WSS and the exciter ring is 0.005 – 0.050 in.
The assembly plant performs a “Rolls Test” on every vehicle that leaves the assembly plant. One of the test per-
formed is a test of the WSS. To properly test the sensor, the assembly plant connects test equipment to the Data
Link Connector (DLC). This connector is located to the right of the steering column and attached to the lower portion
of the instrument panel. The rolls test terminal is spliced to the WSS circuit. The vehicle is then driven on a set of
rollers and the WSS output is monitored for proper operation.
REMOVAL
1. Remove the front rotor (Refer to 5 - BRAKES/HY-
DRAULIC/MECHANICAL/ROTORS - REMOVAL).
2. Remove the wheel speed sensor mounting bolt (1)
from the hub (3).
3. Remove the wheel speed sensor (2) from the hub
(3).
4. Remove the wiring from the clips and disconnect
the electrical connector.
5 - 290
BRAKES - ABS - SERVICE INFORMATION
DR/DH
INSTALLATION
1. Install the wiring to the clips and Reconnect the
electrical connector.
2. Install the wheel speed sensor (2) to the hub (3).
3. Install the wheel speed sensor mounting bolt (1) to
the hub (3). Tighten the bolt to 21 N·m (190 in.
lbs.).
4. Install the front rotor and brake caliper assembly
(Refer to 5 - BRAKES/HYDRAULIC/MECHANICAL/
ROTORS - INSTALLATION).
SENSOR-WHEEL SPEED-ABS-REAR
DIAGNOSIS AND TESTING
REAR WHEEL ANTILOCK
Diagnosis of base brake conditions which are mechanical in nature should be performed first. This includes brake
noise, lack of power assist, parking brake, or vehicle vibration during normal braking.
The RWAL brake system performs several self-tests every time the ignition switch is turned on and the vehicle is
driven. The CAB monitors the system inputs and outputs circuits to verify the system is operating properly. If the
CAB senses a malfunction in the system it will set a DTC into memory and trigger the warning lamp.
NOTE: The MDS or DRB III scan tool is used to diagnose the RWAL system. For test procedures refer to the
Chassis Diagnostic Manual.
REMOVAL
1. Raise the vehicle on a hoist.
2. Remove the brake line mounting nut and remove
the brake line from the sensor stud.
3. Remove the mounting stud (2) from the sensor and
shield.
4. Remove the sensor (1) and shield from the differ-
ential housing (3).
5. Disconnect the sensor wire harness and remove
the sensor (1).
DR/DH
BRAKES - ABS - SERVICE INFORMATION
5 - 291
Нет комментариевНе стесняйтесь поделиться с нами вашим ценным мнением.
Текст