Wagoneer L6-242 4.0L VIN M FI (1988)
Fig. 9 Speed Sensor Air Gap
Fig. 10 Wheel Speed Sensor Spacer Strip
The tone wheels on the front and rear axle shafts are different sizes (117 teeth on front and 51 teeth on rear) and generate different signals for the
same wheel speed. The front tone wheels use a three tooth pole piece pickup while the rears use a two tooth pole piece pickup. The air gap is
different between the front and rear due to this difference in sensors. The air gap between the tone wheels and the sensors is adjustable and is
critical for proper operation of the anti-lock brake system (fig. 9). The proper adjustment procedure is outlined in the Technical Service Manual,
the specifications are:
Front Sensor Gap - 0.013" - 0.019"
Rear Sensor Gap - 0.030" - 0.036"
Some replacement wheel sensors may have a polyethylene spacer strip attached to the sensor contact face (fig. 10). When installing a replacement
sensor with this strip, be sure the spacer strip actually touches the tone wheel. The strips are made in the exact thickness needed for correct air gap
and adjustment is not necessary.
