How to Measure Gear Backlash

by John Stevens J.D.
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Within a differential are two gears, a ring gear and a pinion gear. When the vehicle's driveshaft turns, it rotates the pinion gear. The pinion gear intermeshes with and turns the ring gear. The ring gear transfers the power through the axle shafts to the tires. The amount of play between the ring and pinion gears is referred to as gear backlash. Measuring the backlash is a fairly straightforward task and is a quick way of determining whether a professional adjustment or more extensive service may be necessary.

Step 1

Position the differential securely within the jaws of a large vise with the gears facing up.

Step 2

Attach a dial indicator gauge to the outer edge of the differential. Some gauges feature a magnetic base that attaches to the differential, while other gauges are positioned over a bolt hole within the edge of the differential and secured with one of the differential's bolts. Tighten the bolt through the edge of the differential and into the base of the gauge.

Step 3

Position the contact point of the dial indicator gauge square against any one tooth of the ring gear. The ring gear is the large circular-shaped gear. The contact point is the metal post that, when pressed toward the gauge, causes the gauge needle to move.

Step 4

Turn the adjustment knob on the side of the dial indicator gauge until the gauge needle points to the "0" setting.

Step 5

Rock the ring gear back and forth with your hand while monitoring the gauge needle. The distance indicated on the gauge is the gear backlash.

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