Automotive Terminology can throw you a curve ball, when you hear certain terms which might be used interchangeably, or may indicate different systems used on different cars. Take steering: perhaps your uncle said that the steering box on his truck is worn and needs replacement, then your brother said that his steering rack is leaking and needs replacement. Aren't these the same thing? Let's take a systems approach and break it down for you.
First, the mechanical side of things (we'll discuss power steering later). All cars and light duty trucks use one of two types of steering systems: either a rack & pinion set-up, or a steering box, usually with recirculating balls.
Rack & pinion is on the vast majority of today's vehicles, and has been for the last few decades. It's simple, compact, direct, and gives great steering feel. On this system, when you turn your steering wheel, you turn a pinion gear which is in constant mesh against a rack (a long bar with teeth cut into it). The rack bar moves left and right, which turns your wheels left and right. Tie rod ends at each end of the car allow some up-and-down movement and adjustability. The moveable ends of the rack are covered with a protective boot or bellows, which like an accordion can expand and contract with the rack's movement.
Some of today's heavier trucks have stayed with a steering box, also found on older cars. The typical linkage inside the box is called recirculating ball, because ball bearings circulate in a path. There are other designs such as worm & roller, and worm & sector. All these designs operate by translating the rotating movement of the steering wheel into left/right movement of a pitman arm. The pitman arm connects to the front wheels via a track rod or center link, idler arm (which looks like a pitman arm and is located on the opposite side of the car) and tie rods. This system tends to have more "free play" and more parts to wear compared to a rack & pinion set-up.
The first commercially available automotive power steering system was introduced by Chrysler in 1951. Before that, all cars and trucks had manual, or non-power steering. Power steering works via a pump which produces tremendous hydraulic pressure. The pressure applies force to the steering gear, reducing the steering effort required by the driver. Whether the vehicle has a steering box or a steering rack, the power steering pump is belt-driven, and therefore only operates when the engine is running. Pressure and return hoses direct fluid to a control valve and/or steering cylinder in older designs. In the illustration below, the combination pump/reservoir is driven by a belt, with hoses running to a control valve, then to a power cylinder which applies the pressure to the steering linkages.
Newer vehicles with rack & pinion have control valves and/or pistons built internally in the rack. The power steering fluid sits in a reservoir which may be part of the pump, or may be mounted remotely and connected to the pump via a hose.
One of the newest trends is power steering which is electrically assisted: either a hydraulic pump gets its energy from an electric motor instead of belt; or, the power steering pump itself is an electric motor, with hydraulics no longer needed.
So whichever system you have, you should know that certain components are part of certain systems.
If you have a steering box, or recirculating ball steering, you have:
- A steering box;
- A pitman arm, idler arm, and center link or track rod;
- Tie rod ends.
If you have rack and pinion steering, you have:
- A steering rack;
- Boots or bellows;
- Tie rod ends.
Both systems similarly use a power steering pump, reservoir, and hoses.