【正文】 t suspension members with ball joints. The ball joints allow for steering as the suspension moves up and down. The wheel hubs on frontwheeldrive vehicles rotate on hollow axle stub shafts inside bearings within the steering knuckles.The steering wheel controls the steering gear assembly. This, in turn, moves the knuckle through the steering linkage. Two steering gear designs are in use today, the rack and pinion and recirculating ball.vehicles are designed with responsive steering. As a result, more effort is needed to steer the vehicle when it is moving slowly. Power steering supplies this effort on many vehicles.With power steering doing most of the work, steering ratios are decreased so that the vehicle can be steered with small steering wheel movements. The power steering gear is similar to the standard steering gear. It includes surfaces upon which fluid pressure is applied to aid the driver39。s steering effort. Both rack and pinion and recirculating ball gears may have power assist.Power for the steering gear is provided by an enginedriven pump. The pump forces power steering fluid through a system controlled by a valve. This control valve can sense the driver39。s steering effort. It puts fluid pressure against a pressure surface in the steering system. This fluid pressure takes over some of the effort needed to steer the vehicle.The steering column in the modern vehicle has many parts. It is designed to collapse or fold in a vehicle collision to protect the driver. In some installations, it may be tilted and telescoped to adjust the position of the steering wheel for the fort of the driver. To reduce the chance of theft, it also has a steering gear lock. On many vehicles, it has a transmission lock. Because it is within easy reach of the driver, the steering column may carry the transmission shift control lever, turn signal switch, headlight and dimmer switches, wiper switch, emergency flasher switch, and speed control.Brake SystemsService brakes must be able to stop the vehicle, prevent excess speed when coasting, and hold the vehicle in position while it is stopped on grades. They are designed so the driver can adjust the braking effort to maintain vehicle control. Vehicle control is influenced by brakes as well as the suspension and steering systems. Faults in the brake system can lead to wheel pull during braking. To repair suspension systems, parts of the brake system may require disassembly. For these reasons, the brake system will be discussed briefly in this text.The brake system must provide smooth stopping power that can be controlled by the driver. The force required on the brake pedal must not be so high that the wheels cannot be locked. To meet these braking requirements, minimum braking standards have been set for vehicle brakes.The driver controls the braking force through mechanical, vacuum, and hydraulic mechanisms. The amount of braking increases as more force is placed on the brake pedal. This force is transferred through the brake system to push stationary brake linings against the rotating brake surface. This slows the vehicle as it turns kinetic energy (energy of motion) into thermal energy (heat). Maximum braking occurs just before the wheels lock to cause the tires to slide on the road surface. Maximum braking, therefore, depends on the adhesion between the tire and the road surface. When the tire slides on the road, braking effect is reduced and directional control of the vehicle may be lost.The stationary parts of the front brake assemblies are mounted on the steering knuckle of the front suspension. In the rear, they are mounted on the axle housing or the rear spindle assembly. The castiron brake drum or disc rotates with the wheel .Disc Brake. Disc brakes have discs that rotate with the wheel . The brake disc is usually called a brake rotor. A hydraulically operated piston in a stationary caliper is used to force the lining of the brake pad against the braking surface of the rotor. The friction between the lining and rotor is used to slow or stop wheel rotation. The stationary caliper housing keeps the pads from rotating when they are being forced against the rotating brake disc.Disc brake pads move perpendicular to the face of the brake rotor. In this way, they clamp on the rotor to slow the vehicle motion. The clamping force is proportional to the force the driver puts on the brake pedal.Drum Brakes. Drum brakes use stationary, internal expanding brake shoes with linings. They are mounted inside a rotating brake drum. The brake drum is fastened between the wheeltire assembly and the hub assembly or the axle flange. The brake shoes slow drum rotation when the diameter of the shoes is expanded to bring the lining in contact with the brake surface. This is done by a hydraulically operated wheel cylinder. Fluid pressure from the master cylinder is forced into the wheel cylinders, expanding them. The expansion of the wheel cylinder moves the brake shoe through mechanical linkage to press thelinings against the rotating brake drum. This provides braking action as it slows the rotation of the drum.12 / 12