Installation instructions for FPM sensor, differential mounted

Be sure you have the proper PPE (Personal Protective Equipment) before starting.

Step 1

Block the wheels on one side of the truck and jack up the axle on the opposite side. Be sure truck air pressure is sufficient to release brakes.

Step 2

NOTE: Wear eye protection when drilling the holes required for this installation!

Drill an exploratory 11/32” pilot hole to determine the proper location for the FPM sensor. Position the hole approximately as shown in the picture Figure 1. Make the location well above the axle oil level. As the sensor will not function in oil. The use of an 11/32” drill bit is recommended so the hole can be tapped and plugged with a 1/8” pipe plug.

Figure 1

Step 3

With a flashlight, look through the pilot hole. The ring gear tooth should cover about 1/3 of the sensitive area on the face of the sensor.

NOTE: the position of the gear tooth relative to the hole as seen in figure 2.

Figure 2

The correct position of the hole is important. The sensor must detect an open-air gap between the ring gear teeth, or it cannot count accurately. If the pilot hole is too far from the ring gear. Close it with a pipe plug as described below. If preferred the hole may be spot welded closed.

Step 4

When the mounting hole is properly located relative to the gear teeth, clean the area around the axle vent fitting and remove the fitting. Install a pressure regulator set to 5 PSI (Pounds per Square Inch) maximum and pressurize the axle. This step is necessary to keep chips out of the differential when drilling and tapping the mounting hole.

NOTE: Do not exceed 5 PSI. The axle and pinion seal may be damaged by higher pressure.

Step 5

Rotate the wheel so the drill can pass between gear teeth. Drill a 23/32” hole with the drill pointed toward the center of axle.

Step 6

Tap the hole with a ½”-14 strait pipe tap. The tap must be in good condition, sharp and clean. Be careful to keep the tap at a right angle to the housing so that the locknut will have a good bearing surface. When the hole is tapped, rotate the wheel until a gear tooth is centered in the hole.

Step 7

Screw the sensor in with your fingers until it contacts the gear tooth. Note that the sensor must turn freely, so you will know when it meets the tooth. If the sensor does not turn freely, lubricate the threads and if necessary, run the tap through the hole again.

Step 8

When the sensor touches the gear tooth, back it off ¼ turn and run the locking nut down.

In this and the next step be sure you do not allow the sensor to change position

Step 9

Back the lock nut off while being careful not to change the position of the sensor. Apply silicone sealant, such as 3m form a gasket or equivalent, Beneath the lock nut.

Step 10

Tighten the lock nut securely with a wrench. Be sure not to move the sensor position when tightening nut. Silicone the top of the nut and attach the sensor connector.

If you need to order parts, click here

If you need to look for a manual, click here

Disclaimer: The preceding information is for educational purposes only. Repairing, maintaining, or modifying your equipment can be dangerous. It is your responsibility to ensure that you are aware of all the dangers involved, that you are working in a safe manner and that your repairs, maintenance, or modifications are performed in accordance with all applicable laws and regulations.