Had posted the Doc file so that those interested could download it and share it with others freely. But here goes: 4x4
- This general term is used to describe a vehicle with four-wheel drive. The first figure is the number of wheels, and the second is the number of powered wheels. Another term for four-wheel drive. 4x2
- This term refers to a two-wheel drive vehicle with four wheels, two of which receive power. Another term for two-wheel drive. All-Wheel Drive (AWD)
- All-wheel drive is a passenger-car-based four wheel-drive system that has no two-speed transfer gearbox. It operates similarly to full-time or permanent 4WD, but does not offer Low Range capability for off-road use. This system is more typically available in passenger cars, such as those from Audi and Subaru. Now, however, AWD is cross ing over into sport-utility vehicles, and is used in the BMW X5, Oldsmobile Bravada, Ford Explorer V8 and Mercury Mountaineer V8. Angle Of Approach
- When viewed from the side, this is the angle between the ground and a line running from a front tire to the lowest-hanging com ponent directly ahead, usually the front bumper. This angle gives an indication of how steep a ramp a vehicle can negotiate without damage. It also allows the driver to judge a vehicle's ability to climb over rocks and logs without hitting -and potentially damaging the front part of the vehicles body or chassis.
Angle Of Departure
- In side view, this is the angle between the ground and a line running from a rear tire to the low est-hanging component directly behind it, usually the rear bumper or trailer hitch. Similar to the approach angle, the departure angle indicates a vehicle's ability to drive off a ramp or obstacle without damaging the rear of the SUV.
Anti-lock Braking System - This braking system senses any significant difference in wheel speed from one wheel to another, when a vehicle is braking hard. When any of the wheels begin to lock up (completely stop rotating), ABS
automatically reduces the braking forces to that wheel or wheels in order to keep all the wheels rolling -to prevent brake-induced skidding. ABS
can control all four wheels (most cars and SUV’s have this system) or only two (this is found on some pickup trucks and SUV’s). The system can group wheels together in "channels" of operation (i.e., a three channel system on a four-wheeled vehicle) or have one channel for each wheel (four-channel ABS
Axle Articulation - This term indi cates the ability of one axle to move vertically relative to the chassis or its fellow axle -left wheel up, right wheel down (or vice-versa). It is the measure of the ease with which wheels stay in contact with the ground (and retain traction) on a very bumpy, uneven trail. Box-Section Frame
- This term refers to the characteristics of a frame when viewed in cross section. A box-section frame is constructed using four sides of steel to create a box, as opposed to a C-section or even I-section frame (which would look like those letters in cross section). Brake Fade
- As brakes heat up with hard or repeated use, their effectiveness usually diminishes. This is called brake fade. Brake Lockup
- In braking, lockup describes the point at which a tire starts to skid (stops rotating while the vehicle is in motion) in an emergency-stopping situation. A tire's maximum braking force is developed when it is on the verge of lockup, so a car's shortest stopping distances are produced when its front and rear tires are held just short of lockup. Anti lock brakes (ABS
) prevent wheel lockup, giving the advantage of simultaneous steering and braking ability (a locked wheel cannot be steered). Center Differential
- Rear-wheel drive cars need a rear differential to power the right and left rear wheels and let them turn at different rates of speed when cornering. Front-wheel-drive cars need a front differ ential for the same reasons. Vehicles with full-time or permanent four-wheel drive require a center differential (or similar device, such as a viscous coupling). In a tight turn, all four wheels travel at different speeds. A center differential receives power (or, more correctly, torque) from the transmission (or transfer box) and sends this torque to the front and rear dif ferentials, while allowing the front and rear wheels to travel at different rates. (See "Differential" and "VISCOUS Coupling.") Chassis
- This term can describe a vehicle's structural elements or the collection of mechanical components attached to its frame. In vehicles with unitized or "unibody" construction, the chassis comprises everything but the bolted-on body panels of the car. In vehicles with a separate frame, chassis usually refers to the frame. Coil Spring
-Used in a suspension system, a coil spring consists of a bar of resilient metal (usually a steel alloy) wound into a spiral form. It can be compressed repeatedly or extended without permanent deformation. Constant-Velocity joint -
A "CV" joint is a type of universal joint, usually used between the front half-shafts and front spindles/wheels in a front-wheel-drive or four-wheel-drive vehicle. CV joints are engineered to transmit power more smoothly (compared with universal joints) as they move through two planes. They are also less prone to driveline vibrations. Crossmember
- This component of a frame (or sub frame), placed transversely, connects to and strengthens longitudinal frame rails. Differential
-A differential transfers power (more accurately, torque) from the transmission or transfer gearbox to the axles/wheels, and allows the axles and wheels to turn at different speeds (so the vehicle can turn corners without drive train wind-up -the wheels on the outside of a curve turn faster and travel a greater distance than the inside wheels). While most differentials are mechanical gear-driven devices, sometimes a viscous coupling (VCU) or a multi-plate transfer clutch pack (MPT) can act in place of a differential. Differential Lock
- The main disadvantage of an "open" differential is that the usable torque is restricted by the wheel with the least traction. A differential lock literally locks out the differential action and forces torque to be split equally between each wheel (or each axle) for maximum traction. In a rear wheel drive vehicle, for instance, locking the rear differential locks the left and right rear wheels together so that both receive equal torque. In a full-time or permanent 4WD vehicle, locking the center differential locks the front and rear driveshafts together, sending equal torque to the front and rear axles. While locking a differential helps increase traction, it makes steering more difficult on high-traction surfaces because it tends to force the vehicle to travel in a straight line. Disc Brakes
- This type of braking system consists of a disc or rotor that rotates at the same speed as the wheel to which it is attached, straddled by a caliper. The caliper contains brake pads, operated by small pistons, that squeeze against the surface of the disc to slow it down or stop it. Disc brakes operate more efficiently at high temperatures and wet conditions than drum brakes. Drive shaft
- The drive shaft transmits power from the transmission or transfer gearbox to the differential. A four-wheel drive vehicle has at least two drive shafts -one running to the front differential and one to the rear. Also known as propeller shafts or prop shafts. Drive train
- Also called a powertrain, this term describes all of a vehicle's components that produce power and transmit power to the wheels -the engine, transmission, transfer case, drive shafts, differentials, axle shafts and wheel hubs. Drum Brakes
- A drum brake uses a drum-shaped (cylindrical) housing, usually made of cast iron, that is attached to the wheel and rotates with it. Inside the drum are curved brake shoes that are forced into contact with the inner drum to provide braking. Drum brakes are simple and generally effective, but less efficient than disc brakes under heavy use or when wet. Engine Braking
- This term describes the driving technique of slowing a vehicle by taking your foot off the throttle, particularly in a lower gear (such as first gear/Low Range). Engine braking uses the compression of the engine and the low gearing of the trans mission/transfer gearbox to slow the vehicle. Final-Drive Ratio
- This is the ratio of the gear set (usually the differential) that is farthest from the engine. A ratio of 3.90:1 means the drive shaft turns 3.90 times for every one turn of the wheels. Generally speaking, the higher the number, the better the vehicle's initial acceleration and pulling power. The lower the number, the better the vehicle's fuel economy: Full-Time 4WD
- This drive system offers both a 2WD and 4WD mode. Four-wheel drive can be engaged on dry pavement for normal on-road driving because this system uses some type of center differential. A typical full-time 4WD system offers 2WD, 4WD "Auto" and 4WD Low. Virtually all full-time 4WD systems also have a two-speed transfer gearbox.
Remaining terms in next post.....