Rack and pinion
The rack and pinion is probably the simplest of all the steering systems. It is mounted on the front cross-member. It is attached to the front wheels via tie rods and the steering wheel via a column. The steering column is usually telescopic or collapsible so in the event of a frontal impact the column collapses. This is a safety feature to prevent damage to the driver. The rack and pinion, usually called the steering rack consists of:
- Rack. The rack is a metal bar flattened on one side with teeth machined into the surface and inner tie rods connected to each end.
- Pinion. The pinion if fixed to the end of the steering column and it too has teeth machined into it. When the steering wheel is turned, the teeth on the pinion engage with the teeth on the rack and move the rack in its housing. This moves the inner tie rods, which in turn moves the tie rod ends and eventually the wheels.
- Housing. The housing is the place where most of these parts live. A bearing in the top of the housing carries the pinion shaft and allows it to turn freely. The rack sits on either bearings or metal bushes in the housing. This both allows the rack to move freely and also minimises the about of free-play. The housing is sealed at the top with a rubber seal and at the sides with rubber covers called steering rack boots. This keeps foreign matter from entering into the housing and causing premature wear.
- Inner tie rods. The inner tie rods are connected at each end of the rack with a ball and socket type arrangement. The socket is in the rack and the ball is on the end of the tie rod and this set up allows the inner tie rods to move through angles, which is necessary when steering over bumps and potholes. The outer end of the tie rod is threaded to allow the tie rod end to be screwed on. This is arrangement also facilitates wheel alignment adjustment.
- Tie rod ends. The part most likely to wear in a steering is the tie rod end. This is what connects the steering rack to the wheels and suffers the most abuse. Every time your vehicle hits a kerb, runs over a speed bump or drives into a pothole the tie rod end is under stress. Like the inner tie rod it has a ball and socket joint and this can wear out.
Power steering
Most cars have power steering.
A vane type oil pump, which is bolted to the engine and driven by a fanbelt, generates fluid pressure when the engine is running. This fluid pressure is applied to the steering through valves in the steering rack and helps with the rack movement.
When the engine is running and the steering wheel is turned to one side, the fluid, under pressure, comes into the valve body and is directed to one side of the rack. This fluid puts pressure on a piston and assists the movement.
When the steering wheel is turned the opposite way, the pressure is applied to the other side of the piston.
Power steering fluid level should be checked regularly.
The system should be flushed out completely and refilled with fresh fluid in accordance with the vehicle manufacturer's service schedule.
Power steering fluid
Power steering fluid should be checked regularly to ensure it is filled to capacity.
The fluid can be checked via the reservoir.
For the specific location relating to your vehicle please check your owner’s manual.
Only use the recommended oil for your car, this information can be found in your owner’s manual.
Never over fill the reservoir.
If the power steering fluid needs regular refilling contact your nearest RAC Auto Services site for advice.