How to Use a Jegs Pinion Depth Tool

by Steven Douglas

A Jegs Universal Pinion Depth Setting Tool may used to measure the exact pinion depth of automotive differential components. A Jegs pinion depth tool is similar in design to pinion depth measuring tools produced by other manufacturers, and is used in the same fashion. Measurements are taken by attaching the tool to the machined bearing cap (mating surface) in the differential housing (with supplied clamps), then checking the measured distance to the pinion gear. Learning to use this tool is easy, but requires a bit of practice to become proficient.

Step 1

Inspect the pinion gear exterior to locate the proper dimension of the gear--this dimension is usually etched on the surface of the gear. The dimension represents the required distance (target depth) from the bearing center line to the rear face of the pinion gear. Record this dimension. (It might look like 1.201, for example.)

Step 2

Zero out the dial indicator (on the pinion depth tool) using the calibrating tube that came supplied with the tool. Loosen the collet (neck screw), then place the extension tube inside the calibrating tube. Slide the dial indicator slowly into the collet region, until the gauge needle reads "0," then re-tighten the collet. Be careful not to move anything when tightening the collet. This calibration step (similar to calibrating a scale) is important since it adjusts the tool so that the measured distance is the distance displayed on the tool, with no tool error present.

Step 3

Attach the pinion depth tool to the rear end of the differential housing (with the supplied mechanical clamps). Measure the distance between the machined bearing cap surface to the bottom surface of the bore (the tool will visually display measured distances, so read the display indicator once the center probe of the tool makes contact with the bottom of the bore hole). Since the bore is slightly rounded, measure several areas around the bore to help determine the lowest point within the bore hole (move the tool around slightly so that you measure several spots within the bore). Record the deepest measurement attained.

Step 4

Install one of several extension tubes supplied with the tool kit onto the tool (pick an appropriate extension tube based upon where you clamp the tool onto the differential housing; these extension tubes simply extend the reach of the internal probe, so that you may mount the tool away from the bore hole--if necessary-- then recalibrate it.) Set the pinion squarely onto the machined cap surface. Measure the pinion depth with the extension now contacting the pinion gear at a spot near the housing on which the tool is mounted. Reposition the tool so that you measure a spot about 1 inch away. Place a shim beneath the tool, if necessary, to make sure it is square with the pinion. (The shims are used to add "depth" beneath the surface of the tool to raise it slightly if necessary.)

Step 5

Measure the pinion depth, then add or subtract pinion bearing shims beneath the pinion gear to attain the desired dimension (target depth). Add or subtract shims by placing each shim beneath the pinion gear until the measured pinion depth is equal to the target pinion depth as noted on the exterior of the pinion gear. It make take repeated attempts using different shim thicknesses until you locate the proper shim to elevate the pinion gear enough to attain the exact target depth. (For example, if the current measured pinion depth equals 1.193, and the target pinion depth equals 1.201, then the correct shim to use would measure .008 in thickness, since 1.193 plus 0.008 equals 1.201.)

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