Recirculating-ball Steering
Recirculating ball steering systems have been used in many trucks and SUVs.The linkage that turns the wheels is slightly different than a rack and pinion system.Recirculating ball steering contains a worm gear.You can image the gear in two parts.The first part is a piece of metal with a threaded hole in it.The outside of the block has gear teeth cut into it,which engage a gear that moves the pitman arm.
The steering wheel is attached to a threaded rod similar to a bolt that is inserted into a hole in the block.When the steering wheel is turned,it turns the bolt.The bolt is not twisted further into the block as a normal bolt would be,but is fixed and secured so as to move the block as it rotates,thus moving the gears that turn the wheel.
Rather than the bolts directly engaging the threads in the block,all the threads are filled with ball bearings that recirculate through the gears as they turn.The balls actually serve two purposes:first,they reduce friction and wear in the gears;second, they reduce slop in the gears.When you change the direction of the steering wheel,the slop is felt - without the balls in the steering,the teeth temporarily touch each other,making the steering wheel feel loose.Power steering in a recirculating ball system is similar to a rack and pinion system.It is aided by supplying high pressure fluid to one side of the block.