Steering Gear: Description and Operation

Fig.1 Ford Rack And Pinion Manual Steering Gear:

Used on Aerostar vehicles, this gear is of the rack and pinion variable ratio type. The variable ratio is obtained by the use of a standard helical involute tooth surface on the pinion and a tooth profile on the rack that varies from the on-center position to the steering stop position, providing two ratios, fast and slow.
The on-center position of the rack provides a fast steering ratio which improves response for highway driving. From the off-center position to the steering stop position on the rack, a slow steering ratio is used to reduce steering efforts for cornering and parking.
The steering wheel, through the column and intermediate shaft, controls the rotation of the gear pinion. Gear pinion rotation causes the rack to move right or left according to driver response. Two tie rod and ball joint assemblies transfer rack motion to the spindles, Fig. 1.