In forward-control vehicles, the steering system is mounted in front of the engine and wheels. The steering box is mounted on the subframe, with the Pitman arm vertical.
A drag link transfers movement of the Pitman arm to a relay lever which has 2 arms, one connected to the drag link, and the other to the idler, by the track rod.
The longitudinal movement of the drag link pivots the relay lever. This transfers the motion through the track rod, to the idler arm, and through the tie-rods to the wheels.
In 4-wheel-drive vehicles with a beam axle, the single track rod connects the steering arms on each wheel assembly, across the vehicle.
In this design, the drag link is connected to an arm on the front of the left-hand wheel assembly. Movement of the Pitman arm is transferred through the drag link to the left-hand wheel, and through the track rod, to the right-hand wheel.
The steering box is offset from the steering column, so 2 universal joints and an intermediate steering shaft are used.
Off-road vehicles of this type, without power assistance, often use a steering damper.
It resembles a shock absorber, and operates on a similar principle. It’s mounted between the track rod and either the rigid axle, or the vehicle frame.
When the vehicle is driven over rough terrain, its purpose is to prevent shocks being transmitted through the steering linkage and back to the steering wheel.
With rack-and-pinion steering, the linkage is simpler, since the rack itself is part of the linkage. Movement of the steering wheel is transferred through the steering column, intermediate shaft, and universal joints, to rotate the pinion, which moves the rack from side to side.
A tie-rod with a ball swivel at each end of the rack relays the movement directly to the steering lever on each wheel assembly.
The rack can thus be considered as the centre track rod of a 3-piece track rod system.
The steering lever or steering arm, is linked to the tie-rod, or track rod, by a flexible ball joint that allows for suspension movement, and steering rotation.
The lever, the stub-axle and the stub-axle carrier can be forged as one piece, and can be referred to as a knuckle.
They can also be made as separate units, and assembled to form one piece.
Each steering system makes provision for adjustment of the linkage, to achieve the manufacturer’s recommended toe-setting.
The track rods or tie-rod ends are threaded, to provide for their lengthening or shortening.
Steering linkages
The steering linkage is a combination of rods, and arms, that transmit the movement of the steering gear to the front wheels.
It must transmit this movement to the front wheels, while still allowing for any up-and down movement they may make, while the vehicle is in motion.
The type of steering mechanism, and the number of linkages, depends on the type of steering box, its location, and the type of suspension on the vehicle.
Passenger cars with independent suspension, and using a worm-type steering box, may have the steering box mounted so that the linkage is in front, or behind, the suspension cross-member.
When the linkage is behind, it is protected by the cross-member from possible damage, and the position of the steering box reduces the length of the steering column.
Steering wheel movement is relayed through the steering gear and Pitman arm, to a centre track rod. The centre track rod is connected to the Pitman arm at one end, and to a steering idler arm, at the other end.
The idler arm assembly is bolted to the vehicle frame, and the idler arm is positioned, parallel to the Pitman arm. It can then relay the steering box movement accurately to the opposite side.
A tie-rod on each side of the vehicle connects each wheel assembly with the centre track rod. Flexible joints on the track rod, and on the ends of the tie-rods, allow for steering and suspension movement.
Joints
Ball joints are swivel connections mounted in the outer ends of the front control arms, and on the steering track rods and tie-rods.
They allow the control arms to move up and down with suspension deflection, and also let the wheel and hub assembly turn for steering.
The ball joint can be a sealed, self-contained unit, fastened to the control arm in a number of ways.
It is made up of a pressed-steel housing, fitted with sintered iron seats, and a hardened ball stud. A taper on the stud locates in a mating taper on the suspension unit, and a rubber seal keeps out dirt and water.
Some ball joints can be dismantled, to replace the seats and the ball stud, and allow for adjustments. Shims between the upper and lower halves of the joint allow free play to be controlled.
Grease nipples can allow for periodic lubrication but most joints to-day are sealed for life, and no regular maintenance is required. On tie-rod ends, the ball joint is usually self-contained and attached to the tie-rod by internal or external threads.
Bushes/bushings
Bushes, or bushings, act as bearings at suspension fulcrum points, to allow for movement of the component, while maintaining its alignment.
They can be metallic, or made of rubber, nylon, or urethane.
In commercial vehicles, metallic bushes are commonly used as shackle bushes for leaf springs. Any force applied to the bush acts through it to the body of the vehicle, which results in a harsher ride.
The mounting pin on a metallic bush is usually drilled to allow for lubricating the bushes.
Rubber bushes isolate noise and harshness, and dampen unwanted vibrations. Rubber bonded bushes can be used to mount the steering rack to the vehicle frame. The rubber absorbs small impacts from the suspension action, without transmitting them to the vehicle. Rubber requires no lubrication.
Spring shackle bushes can be molded to form two halves, to fit into each side of the spring eye, on the swinging shackle. With the spring loaded, and the shackle plates tightened, the rubber is compressed in the eye and at the face of the plates. As the spring deflects, the rubber shears without tearing.
Metalastic, or rubber-bonded, bushes are normally used for the front eye of the spring, at the fixed shackle point, and also in control arm applications.
The bush has a steel outer casing and inner sleeve. The rubber medium is bonded to both, to provide flexibility between them. The outer casing is normally pressed into place in the component. Relative movement between the casing and the inner sleeve causes the rubber to shear without tearing.
In control arm applications, particularly at the rear of a vehicle, the rubber arm may be molded with a voided section. This is known as a compliance bush because it allows the unit or component to comply with a controlled amount of movement in the direction of the void.
This movement relative to the vehicle frame, allows compliance or deflection steer of the road wheels when cornering. Since this influences the steering behavior of the vehicle it is very important the voided section is in its correct, relative position.
