Ford 8.8 Locker 31 Spline with Heavy-Duty Cross Pin Shaft

This is a drop-in automatic locker for the Ford 8.8-inch rear axle with 31-spline axle shafts. It replaces the factory spider gear set inside the existing open carrier case: the two side gears, the four pinion gears and the cross pin all come out, and the locker couplers, spacers, driver pins and springs go in their place. Because the carrier itself stays in the housing, you are not resetting pinion depth, backlash or carrier bearing preload, and the axle ratio does not change.

Fitment is the Ford 8.8 ring and pinion housing with the 10-bolt ring gear and 31-spline axles - the larger-spline version of the 8.8 found in Explorers, later F-150s and axles that have been upgraded from the common 28-spline shafts. Count the splines on the axle end before ordering; a 28-spline 8.8 will not accept this unit. Manufacturer part number is SL F8.8-31, and the heavy-duty cross pin shaft is included in the box rather than sold separately.

On the bench or under the truck the job runs the same way as a spider gear replacement. Drain the axle and pull the differential cover, back out the cross pin bolt and slide the cross pin out, push the axle shafts inward and pull the C-clips, then withdraw both axles. Rotate the old side and pinion gears out of the case window, seat the new couplers with their spacers behind them, load the driver pins and springs, then install the supplied cross pin and bolt and reverse the teardown. Set up your gear oil fill and a new cover gasket or RTV before you drop the pan back on.

What it fixes is the one-wheel-spin problem an open 8.8 has: on wet pavement, in mud or on a launch, the open carrier sends torque to whichever tire has less grip and the truck sits there. A locker of this type keeps both axle shafts driving under power and ratchets - you will hear a click - when one wheel has to turn faster than the other in a corner. That ratcheting is normal operation for a lunchbox locker, not a fault.