rack and pinion

Rack and pinion steering uses a gear-set to convert the circular movement of the steering wheel in to the linear motion required to turn the wheels. It also provides a gear reduction, so turning the wheels is easier.
It works by enclosing the rack and pinion gear-arranged in a metallic tube, with each end of the rack sticking out from the tube and connected to an axial rod. The pinion equipment is mounted on the steering shaft so that when the tyre is turned, the apparatus spins, moving the rack. The axial rod at each end of the rack links to the tie rod end, which is attached to the spindle.
Most cars need 3 to 4 complete turns of the tyre to proceed from lock to lock (from far right to far left). The steering ratio shows you how far to turn the steering wheel for the tires to turn a certain quantity. An increased ratio means you should turn the tyre more to turn the wheels a certain quantity and lower ratios supply the steering a quicker response.
Some cars use adjustable ratio steering. This rack and pinion steering system uses a different number of tooth per cm (tooth pitch) at the heart than at the ends. The result is the steering can be more sensitive when it is switched towards lock than when it’s close to its central position, making the car more maneuverable.
There are two main types of rack and pinion steering systems:
End take off – the tie rods are mounted on the end of the steering rack via the inner axial rods.
Centre take off – bolts attach the tie rods to the centre of the steering rack.
As steering is vital for controlling your car, it’s important to diagnose and repair any steering issues as fast as possible.
The chances are your car has rack and pinion steering.
Thankfully, the fundamentals aren’t hard to grasp at all: it’s about turning rotational motion into linear. When you switch the steering wheel, this turns a steering column, which rotates the attached steering shaft and a worm gear referred to as the pinion. This gear sits on the ‘rack’, a length of metal with some teeth cut involved with it. So as the pinion rotates, the rack techniques either left or right, depending on your steering input.
Power steering provides a device to 1 aspect of the rack with a hydraulically actuated piston inside. A rotary valve directs hydraulic fluid to either the right or left part of the piston – depending on the steering direction – which applies strain on the piston and reducing the effort had a need to move the rack.
The rack-and-pinion gearset does two things:

It converts the rotational motion of the steering wheel in to the linear motion needed to turn the wheels.
It provides a gear reduction, which makes it easier to turn the wheels.
On many cars, it takes 3 to 4 complete revolutions of the tyre to help make the wheels turn from lock to lock (from far still left to far right).