Rack-and-pinion steering has become one of the most common types of steering systems for most modern vehicles; even small trucks and SUVs are equipped with it. It is actually a pretty simple mechanical mechanism. A rack-and-pinion gear-set is enclosed in a metal tube, with each end of the rack protruding from that tube.
A rod, called a tie-rod, connects to each end of the steering rack.
The pinion gear is attached to the steering shaft. When you turn the steering wheel inside your vehicle, the gear spins, moving the steering rack. The tie-rod at each end of the rack connects to the steering arm on the spindle.
The rack-and-pinion gear-set does two main things:
1. It converts the rotational motion of the steering wheel into the linear motion needed to turn the wheels of your vehicle.
2. It also provides some gear reduction, making it easier for you to turn the wheels using the steering wheel of your vehicle.
On most vehicles, it takes about three to four complete turns of your steering wheel to make the wheels go from what is called, lock to lock, in other words from the far left to the far right of the vehicles turning ability.
The steering ratio is the ratio of how far you turn your steering wheel to how far your vehicle wheels turn. For instance, if one complete revolution of 360 degrees of the steering wheel inside the vehicle results in the wheels of the car turning 20 degrees, then the steering ratio is 360 divided by 20, which is 18:1.
A higher ratio means that you have to turn your steering wheel more to get the wheels to turn a given distance. However, less effort is required because of the higher gear ratio.
Generally, lighter, sportier vehicles have a lower steering ratio than larger heavier vehicles and trucks. The lower ratio gives the steering a quicker and faster response. You don't have to turn the steering wheel as much to get the wheels to turn a given distance, which is a desirable outcome for most sports cars. These smaller cars are light enough that even with the lower ratio, the effort required to turn the steering wheel is not excessive.
Power Rack-and-pinion steering
When a power-steering unit controls the rack-and-pinion system, the steering rack has a slightly different configuration.
Part of the steering rack contains a cylinder with a piston in the middle. The piston is connected to the rack. There are two fluid ports, one on either side of the piston. Supplying higher-pressure fluid to one side of the piston forces the piston to move, which in turn moves the rack, providing the power assistance to the steering.
WHAT CAN GO WRONG?
Has your vehicle’s power steering failed or feels heavy?
It is possible that your power steering pump has failed or the rack itself may have a loss of hydraulic fluids through a bad hose or seals and could cause a potential failure. One thing is for sure; it would be wise to tend to the problem as soon as you can. Left unattended and you will soon be struggling with steering a vehicle that seems to be working against you, not with you.
1. Strange Noises
Before the steering pump failure becomes obvious, you will most likely hear some strange noises coming from underneath the bonnet. It is difficult to pin point but it will be a whining or buzzing sound that wasn’t there before.
2. Heavy Steering
On the other hand, you may be noticing a gradual loss of power at your steering wheel, which usually shows up when parking, or slower turning speeds, that could be a sign that your steering rack may be about to fail.
Steering racks tend to fail gradually, but when this starts to occur you must take action before you experience total failure. Otherwise, control of your vehicle becomes impossible and failure could then happen at any time when lest expected. It could be a real threat to you and your passenger’s safety and to the safety of other drivers on the road at that time.
3. Visual Check
To find out if it’s the steering rack that is causing the problem, check the power steering fluid reservoir under the bonnet closely to see if you can see any small metallic pieces of metal floating around in the fluid. If you do, then your steering rack is wearing out and the metallic pieces are the evidence that the rack is coming apart piece by piece.
If you need to fit a replacement steering rack and you are not sure what all this means, then it’s worth talking to one of our Ford & Holden parts specialists. Even if they can’t help, Steve our steering rack expert is sure to be able to give you some sound advice.