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Having the correct amount of preload on the carrier bearings prevents the locker from moving-and thus increasing backlash on the gears-when our 'Stang is flogged. Before calling this project done, Chris checks backlash by mounting a dial indicator on the rear and setting the plunger perpendicular to the teeth on the ring gear, then rotating the ring gear back and forth for measurements. As a rule of thumb, backlash changes roughly 0.007 inch for each 0.010 inch that a differential is moved, either closer to (decreases) or farther away from (increases) the pinion gear's centerline. Chris says from 0.008 to 0.012 inch is OK, but new gears like our 4.30s should be set up more on the tight side, so the backlash will still be within that range after a 100-mile break-in period.