Dodge ram truck 3500 1996 Service Manual page 233

B R BRAKES 5 - 49
DESCRIPTION AND OPERATION (Continued)
gle strand of wire. The sensor sends a small AC
signal to the CAB. This signal is generated by mag­
netic induction. The magnetic induction is created
when a toothed sensor ring (exciter ring or tone
wheel) passes the stationary magnetic WSS.
SENSOR
WIRE
CONNECTOR
REAR BRAKE
SPEED
SENSOR
ASSEMBLY
SENSOR \L
WIRE
AXLE
HOUSING
SENSOR
COVER
/ SENSOR
' / W I R E
SPEED
SENSOR
5). Every time a tooth of the exciter ring passes the
tip of the WSS, .an AC signal is generated. Each AC
signal (positive to negative signal or sinewave) is
interpreted by the CAB. I t then compares the fre­
quency of the sinewave to a time value to calculate
vehicle speed. The CAB continues to monitor the fre­
quency to determine a deceleration rate that would
indicate a possible wheel-locking tendency.
MAGNETIC
C O R E
V
C O I L *
AIR GAP
C A B
J9305-37
Fig. 3 Rear Wheel Speed Sensor Location
The exciter ring is press fitted onto the differential
carrier next to the final drive ring gear (Fig. 4). For
service replacement of the exciter ring, refer to sec­
tion 3 of this Service Manual.
Fig. 4 Exciter Ring Location
When the ring gear is rotated, the exciter ring
passes the tip of the WSS. As the exciter ring passes
the tip of the WSS, the magnetic lines of force of the
sensor are cut, causing the magnetic field to be
moved across the sensor's windings. This, in turn
causes current to flow through the WSS circuit (Fig.
8020cd59
Fig. 5 Operation of the Wheel Speed Sensor
The signal strength of any magnetic induction sen­
sor is directly affected by:
• Magnetic field strength; the stronger the mag­
netic field, the stronger the signal
• Number of windings in the sensor; more wind­
ings provide a stronger signal
• Exciter ring speed; the faster the exciter ring
rotates, the stronger the signal will be
• Distance between the exciter ring teeth and
WSS; the closer the WSS is to the exciter ring, the
stronger the signal will be
The rear WSS is not adjustable. A clearance speci­
fication has been established for manufacturing toler­
ances. I f the clearance is not within these
specifications, then either the WSS or other compo­
nents may be damaged. The clearance 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 performed 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 left of the steering column
and attached to the lower portion of the instrument
panel (Fig. 6). The rolls test terminal is spliced to the