June 2nd, 2006
Universal Joint (U-joint)
The Universal joint (U-joint) connects the drive shaft to the transmission output shaft and the differential pinion gear shaft. This joint must be flexible enough to allow changes in the driving angle (road incline) and the drive shaft. This way, the torque is constantly transmitted when the rear axle is moving up and down. Smaller U-joints are used to route the turning motion of the steering wheel through the steering column to the steering box. There are two types of U-joints, the cross and roller type and the ball and trunnion type. The cross and roller type is used the most; it allows the drive shaft to bend. The ball and trunnion type less frequently used; it allows the drive shaft to bend and also permits backward and forward motion of the drive shaft.
Constant Velocity Joints or homokinetic or CV joints allow a rotating shaft to transmit power through a variable angle, at constant rotational speed, without an appreciable increase in friction or play. They are mainly used in front wheel drive and all wheel drive cars. However, rear wheel drive cars with independent rear suspensions typically use CV joints at the ends of the rear axle halfshafts. Audi Quattros use them for all four half-axles and on the front-to-rear driveshaft (propeller shaft) as well, for a total of ten CV joints.
CV Joint Problems
Wear in the outer joint usually shows up as vibration at certain speeds, a bit like the vibration caused by an unbalanced wheel. To determine if the joint is worn, find a big empty car park and drive the car slowly in tight circles, left and right. Worn joints will make a rhythmic clicking or cracking noise. Wear in the inner joints shows up as a “clunk” when applying power, or if severe, when lifting off the throttle.
Partial seizure causes a strange “pattering” sensation through the suspension. It is caused by the joint overheating, which in turn is usually caused by the outer joint gaiter having split, allowing the joint to throw out its grease. If caught in time, you can clean the joint carefully, repack with grease and replace the gaiter. Kits which include the grease, gaiter and retaining clips are available from most motor factors. Some universal gaiters are split lengthwise enabling them to be fitted without having to disassemble the wheel hub and CV joint.
June 2nd, 2006
Automatic transmission fluid is a specially formulated oil containing numerous additives to withstand grueling operating conditions. There are several different types of automatic transmission fluids and should be used according to the recommendation in your car’s owner’s manual. Automatic transmission fluid serves a multitude of purposes. Among other things, it cleans, cools, lubricates, transmits force, transmits pressure, inhibits varnish build-up and protects the transmission on a day-to-day basis
Transmission Fluid Dip Stick is a long metal rod that goes into the transmission. It serves check how much transmission fluid is in the transmission. The dip stick is held in a tube; the end of the tube extends into the transmission. It has measurement markings on it. If you pull it out, you can see whether you have enough transmission fluid, or whether you need more by the level of fluid on the markings. Most manual transmissions do not have dipsticks, instead they use a filler hole which is at the same level as the correct oil level. When the oil is topped up or refilled, the mechanic simply adds oil until the filler hole’s level is reached.
June 2nd, 2006
Timing Belt
The job of the timing belt is to turn the camshaft(s) at exactly 1/2 the speed of the crankshaft while maintaining a precise alignment. This means that the crankshaft will make two revolutions for every revolution of the camshaft. Engines will have at least one camshaft, or as many as four camshafts in some of the V-type engines. The camshaft causes the intake and exhaust valves to open and close in time with the pistons which move up and down in the cylinders. The valves must open and close at exactly the right time in relationship to the piston movement in order for the engine to run properly.
Timing belts are typically inaccessible and difficult to inspect. Replacement at specific intervals is recommended by the manufacturer. The manufacturer may also recommend the replacement of other parts, such as the water pump, when the timing belt is replaced because the additional cost to replace the water pump is negligible compared to the cost of accessing the timing belt. Failure of the timing belt will leave the engine non-functioning. Depending on the design of the engine, the piston and valve paths may “interfere” with one another and incorrect timing in their movements may result in the piston and valves colliding. (Such designs are also called “interference head” or “interference engines”. Conversely, non-interfering engines are called “free-wheeling” or “non-interference” engines.)
The automobile engine uses a metal timing chain, or a flexible toothed timing belt to rotate the camshaft. The timing chain/belt is driven by the crankshaft. The timing chain, or timing belt is used to “time” the opening and closing of the valves. The camshaft rotates once for every two rotations of the crankshaft.
June 2nd, 2006
Starter Motor
A starter is an electric motor needed to turn over the engine to start it. A starter consists of the very powerful DC electric motor and starter solenoid that is attached to the motor.A starter motor requires very high current to crank the engine, that’s why it’s connected to the battery with large cables. Turning on the ignition switch releases a small amount of power from the battery to the solenoid above the starter. This creates a magnetic field that pulls the solenoid plunger forward, forcing the attached shift yoke to move the starter drive so that its pinion gear meshes with the engine’s crankshaft flywheel. When the plunger completes its travels, it strikes a contact that permits a greater amount of current to flow from the battery to the starter motor. The motor then spins the drive and turns the meshed gears to provide power to the crankshaft, which prepares each cylinder for ignition.
After the engine starts, the ignition key is released to break the starting circuit. The solenoid’s magnetic field collapses and the return spring pulls the plunger back, automatically shutting off the starter motor and disengaging the starter drive. When the starter is not in use, the drive unit is retracted so that its pinion is disengaged from the flywheel. As soon as the starter is activated, the forward movement of the solenoid plunger causes the shift yoke to move the drive in the opposite direction and engage the pinion and flywheel. The pinion is locked to its shaft by a clutch that unlocks if the engine starts up and the flywheel begins turning the pinion faster than its normal speed. By allowing the pinion to spin freely for a moment, the clutch protects the motor from damage until the drive is retracted.
June 2nd, 2006
Car Springs
There are two kinds of springs, leaf springs and coil springs. Springs have life spans that are determined by the number of cycles they can withstand over a certain period of time. If a spring breaks while a car is being driven, the car will suddenly lurch downward. The bottom of the car might be damaged, or you might lose your muffler! Leaf springs are made of individual springs, or plates. If you break one plate of your leaf spring, it won’t be noticeable, but your car might begin to lean to one side or the other. Coil springs, if they break, will suddenly drop the front or rear end of your car and impair driving under the normal conditions of full suspension travel.
Contrary to popular belief, springs do not appreciably “creep” or get “tired” with age. Spring steel has a very high resistance to creep under normal loads. The sag observed in older automobiles is really due to the springs being occasionally compressed beyond their yield point, causing plastic deformation. This can happen when the vehicle hits a large bump or pothole, especially when heavily loaded. Most vehicles will accumulate a number of such impacts over their working life, leading to a lower ride height and eventual bottoming-out of the suspension.
June 2nd, 2006
Car Spoiler
A spoiler is a kind of wing that is mounted on the rear of the car in a horizontal position. Its function is to provide high-speed stability. In most cars, the spoiler is purely cosmetic, as a car has to be going over 100 mph to take advantage of the aerodynamics of the spoiler. Some mini-vans also make use of a spoiler, but it’s upside down, and angled. This type of a rear spoiler only keeps the rain off the rear window.
Spoilers generally work by disrupting the airflow going over a car. This disruption has two primary effects:
- reducing the amount of lift naturally generated by the shape of the car, and
- increasing the amount of positive pressure downward through the vehicle
The result of these two effects is the same: increasing the force between the tire and the road surface, thereby increasing traction. This increase in traction allows a vehicle in motion to brake, turn, and accelerate more aggressively without tire slippage. Additionally, this is accompanied by an increase in aerodynamic drag.
In nearly all cases, downforce and drag increase as the speed of the vehicle increases. Thus, spoilers that are effective at very low speeds often generate excessive drag at high speeds, and spoilers that work well at high speeds are often ineffective while moving slowly. Some spoilers have adjustable components so they can be tuned. Formula One cars, for instance, feature different settings so the car can be optimized for short, low-speed tracks or larger, high-speed ones.
Types of spoilers
Although the most recognizable spoiler is the wing spoiler, there are actually many different types of spoilers.
- A wing spoiler is an airfoil is suspended above the body of the vehicle.
- A lid spoiler (commonly trunk lid spoiler, lip spoiler, or boot lid spoiler) is often a ridge of plastic or metal attached directly to the top of the trunk lid.
- A roof spoiler is a small ridge of plastic or metal attached to the very back of the roof, usually just above the rear window.
- A splitter is a spoiler attached to the front bumper, very close to the road surface, sometimes known as a “front spoiler” or on stock or stock-appearing cars as an “air dam.”
June 2nd, 2006
The instrument that indicates distance travelled by a vehicle. Usually located near the Speedometer the Odometer tells the driver how far he has gone since last reset and also how far the car has travelled in its life. The KM reading on the Odometer go a long way to determine the resell value of cars, however the older style analogue odometers can easily be changed to show lower KMs and the electronic, digital display odometers are also not tamper proof.
June 2nd, 2006
Speedometer
A speedometer measures the speed of a vehicle. Traditional automotive speedometers are driven by a flexible, sleeved cable that is rotated by a set of small gears in the tail shaft of a transmission. The speedometer itself is two rotating, barrel-shaped magnets. One magnet is connected the sleeved cable, and the other is connected to the speedometer needle. These magnets are calibrated such that a given revolution speed of the flexible cable corresponds to a specific speed indication on the speedometer. This calibration must take into account several factors, including ratios of the tailshaft gears that drive the flexible cable, the final drive ratio in the differential, and the diameter of the driven tires. The speedometer mechanism often also drives an odometer. In Australia Law allowes a 10% error for measurement. However in some states (such as Victoria and NSW) speed camera’s tolerate less than 10% making it hard to accurately measure your speed.
Speedometer Cable | Wires
The speedometer cable is connected either to the gearbox output shaft, transmission shaft, or differential. Speed and record mileage is measured by the rotation of these shafts. This information is sent back through the cable where it is recorded on the speedometer. The speedometer and odometer are driven by a cable housed in a flexible casing, which is connected to a gear in the transmission. Speedometer cables break as the result of age, lack of lubrication, or because the cable casing has sharp bends. It may also break from too much friction in the speedometer head.
June 2nd, 2006
Spark Plugs
A spark plug (sometimes in British English, a sparking plug) is an electrical device that fits into the cylinder head of some internal combustion engines and ignites compressed aerosol gasoline by means of an electric spark. Spark plugs have an insulated center electrode which is connected by a heavily insulated wire to an ignition coil or magneto circuit on the outside, forming, with a grounded terminal on the base of the plug, a spark gap inside the cylinder.
These are spaced to provide a gap for firing an electrical spark to ignite air-fuel mixtures. The high-voltage burst from the coil via the distributor is received at the spark plug’s terminal and conducted down a center electrode protected by a porcelain insulator. At the bottom of the plug, which projects into the cylinder, the voltage must be powerful enough to jump a gap between the center and side electrodes through a thick atmosphere of fuel mixture. Fuel is ignited in the cylinder when the spark bridges the gap.
June 2nd, 2006
Shock Absorbers
shocks provide resistance by forcing hydraulic fluid (oil) through valves in the piston as it moves up and down. Because the oil cannot be compressed, only a certain amount of fluid can be forced through these valves, which creates resistance to the vehicle movement. Premium shocks and struts are superior to regular hydraulic shocks because air in the shock is replaced by pressurized nitrogen gas. This advancement in technology prevents bubbles from forming in the hydraulic fluid. These bubbles, called foaming, reduces the ability of shocks to provide resistance and prevent bounce. Gas shocks also quicken the response of a shock’s movement thereby increasing comfort and control under all conditions.
The operating principle of direct-acting hydraulic shock absorbers is in forcing fluid through restricting openings in the valves. This restricted flow serves to slow down and control rapid movement in the car springs as they react to road irregularities. Usually, fluid flow through the pistons is controlled by spring-loaded valves and the hydraulic shock absorber automatically adapts to the severity of the shock. If the axle moves slowly, resistance to the flow of fluid will be light. If it is rapid or violent, the resistance is stronger, since more time is required to force fluid through the openings. By these actions and reactions, the shock absorbers permit a soft ride over small bumps and provide firm control over spring action for cushioning large bumps. The double-acting units must be effective in both directions because spring rebound can be almost as violent as the original action that compressed the shock absorber.
Do you experience excessive bounce (3 or more bounces) when crossing an intersection or dip?
When stopping quickly, does your vehicle rock back and forth several times?
While applying your brakes firmly at higher speeds, does your vehicle have a tendency to drift left or right?
When changing lanes quickly does your vehicle rock or sway from side to side?
On a tight curve like a freeway ramp, does your vehicle lean and sway giving it an uneasy and disconnected feeling?
If yes to any of the questions above, it is worth getting your shockies checked!
June 2nd, 2006
Shock Absorber Struts
A strut is a structural piece designed to resist pressure in the direction of its length. On typical “McPherson Strut” use, the shock absorber is built into the strut. Most shock absorber struts are hydraulic units. Like the hydraulic shock struts, faulty units must be replaced as an assembly. Shock absorbers and struts do more than just provide a comfortable ride. Their most important function is to influence the control and handling characteristics of your vehicle. Without them, a vehicle would continually bounce and bound down the road, making driving extremely difficult. Shocks and struts are designed to help keep your tires on the road. They control the action of the spring to resist bottoming out like when you hit a pothole and keep the movement of the springs under control when they rebound.
Another similar front suspension system is called the “hydraulic shock strut.” This strut serves as a shock absorber and replaces the upper control arm. The coil spring, however, is located between the lower control arm and the body structure instead of being mounted directly on the strut.
