We checked the backlash using a plunger-style dial indicator equipped with a magnetic base so it would to stick to the housing. The proper orientation is shown here, and we checked the backlash at four different points along the gear. A backlash spec will be provided with new gears, but we shot for 0.009-inch to 0.011-inch with our used set. Moving shim thickness away from the gear teeth side and toward the back of the ring gear will decrease backlash, and vice-versa. Here’s a good rule of thumb: moving the carrier 0.010-inch will usually change backlash by 0.007-inch.
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Paint three or four gear teeth (both sides) with a thin coat of marking compound that will show whether the pinion depth is correct. Turn the pinion gear while applying a small amount of drag (with your hand) to the ring gear. Check the pattern on the drive (steeply angled) and coast (flatter angled) sides of the teeth. Referencing our pattern to a chart in the ’65 Chevelle overhaul manual told us our pinion shim was too thick. Note how the drive pattern is shifted toward the heel (inside) of the tooth, while the coast pattern is biased toward the toe (outside).
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We pulled apart our 12-bolt three more times, each time swapping in a thinner pinion shim. Then re-adjusted backlash and re-checked the pattern until we finally had something that looked optimal. Note how the drive pattern is nicely centered and even along the height of the tooth. The pinion shim that gave us the best pattern was 0.012-inch, which was 0.003-inch thinner than the thinnest shim in the ND installation kit (we got the thinner shims from Byers Performance). Consulting with an experienced professional like Byers can bail you out of a similar situation.
The carrier and pinion must come out one last time so the new crush sleeve and pinion seal can be installed. The crush sleeve fits between the inner and outer pinion bearings, and must be crushed to length to bring the bearings closer to the races until they’re preloaded a small amount (15-25lb-ft of drag at the yoke). We ever-so-slightly crushed the sleeve in a hydraulic press to get it started, and then muscled it down using our pinion yoke turning tool and a 3/4-inch breaker bar to turn the nut. It may take nearly 300 lb-ft to initially crush the thing, so don’t be shy. When you feel a small amount of drag as you turn the pinion, stop and measure the preload. We used a fish scale, mounted one foot out from the pinion nut, to measure drag torque. Two pounds exerted at 12 inches away from center is 24lb-ft, so we stopped when we got that reading. Now you can re-install the carrier, and add a 0.005-inch shim (again, from Byers Performance) to each side to preload the bearings.