Model AA Ford has a four-speed manual gearbox. The additional gear in the transmission is a "granny" or "creeper" first gear with a higher reduction ratio than the first gear on a Model A Ford to provide more torque to move a loaded truck. The second through fourth gears on the Model AA transmission were similar ratios to the first through third gears on the Model A transmission. The Model AA transmission also featured a lock-out on the shift knob for reverse that required a lever to be activated with the thumb so reverse could be engaged. This was done to prevent accidental engagement of reverse while the truck was in motion. Early trucks had a worm gear rear-end that limited the top speed of the truck. That rear-end was replaced by a ring and pinion differential to improve the speed of the truck. The later differential came with high speed and low speed options. Later models were fitted with braces on the outer casing of the rear-end to provide additional support to the rear-end housing.