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Glossary Of 4x4 Terms

Posted in Features on March 1, 2006
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A-arm Triangular-shaped suspension component with two pivot points connected to the truck's frame and one point attached to the spindle.
ABS Antilock Braking System
add-a-leaf An extra spring leaf that is added to the spring pack.
after-cat system An aftermarket exhaust system that attaches to the outlet side of the catalytic converter and generally consists of a free-flow muffler, new tubing, and mounting equipment.
airbox Enclosed chamber that routes fresh air to the carburetor or intake manifold. Some trucks use an airbox with an integral filter; some use a remote filter at the airbox's intake duct.
air dam Full-width panel just below the bumper, designed to reduce or modify airflow under the truck, which improves aerodynamics but limits ground clearance.
air-down To lower the air pressure in tires. Airing down increases traction and smooths out the ride over rough terrain.
air/fuel mixture The ratio of air to gasoline that makes the fuel mixture. Theoretically, the perfect ratio is 14.7:1.
Air Locker A selectable locking differential manufactured by ARB that uses compressed air to engage the side gears.
all-wheel drive (AWD) A system in which all four wheels are driven but that lacks a multirange transfer case.
analog Gauge or display that shows a reading such as mph, rpm, or fuel level with a dial and moveable needle indicator.
anodize To apply a colored or clear oxide coating to an aluminum component through an electrical charge.
antisway bar Suspension component that prevents excessive side-to-side body sway. Syn. sway bar.
approach angle The maximum incline angle that a truck can climb or descend without hitting its front.
ARB 1. Air Resources Board. 2. Manufacturer of the Air Locker differential and other off-road products.
aspiration An engine's breathing system.
axle hop When a truck's axlehousing rotates opposite the direction as the tires under acceleration, then snaps back to its original position relative to the chassis. Sometimes, this motion is repetitive until the driver reduces the degree of acceleration. Syn. axlewrap.
axlehousing Exterior nonrotating housing that contains the axleshafts, differential, and the gears that drive the wheels.
axlewrap A condition where the rotational load from an axle is placed on the leaf spring. Springs are flexed into an "S" shape, storing spring energy until the tires slip.

backpressure Resistance to the free flow of exhaust gases.
backspacing The distance between a wheel's outer inboard edge and its mounting flange.
baffle 1. Plates, panels, or barriers inside a muffler that reduce sound. 2. A condition resulting from mysterious vehicle vibrations.
balance tube Short, laterally positioned pipe connecting the exhaust pipes on a dual-exhaust system. Used to equalize gas pressure between the two pipes.
ball joint A flexible joint consisting of a ball used in a socket, mainly in front suspensions because it can accommodate a wide range of angles.
BDC Bottom Dead Center, the lowest point of a piston's travel within the cylinder.
bead 1. The inner lip of a tire that attaches to the wheel. The exterior rubber bead conceals an embedded wire reinforcement. 2. In welding, a narrow half-round line where two pieces of metal have been joined.
bead lock A two-piece system that clamps the tire to the rim, especially helpful when airing down your tires for off-roading.
beater A truck that is rough or dented on the outside but might be mechanically sound. Syn. Bomber.
beefed-up 1. A 4x4 that is stronger than stock. 2. An after-dinner condition on the trail.
beltline 1. Body line running from front to back on a truck's side that visually separates the lower body from the lower edge of the greenhouse, the roof, and window assembly. 2. A measurement that increases as we get older.
bench race To talk about your truck and your driving feats as if they were fish stories.
bezel Trim ring, usually chromed or polished, that surrounds headlights or gauges.
bicycle To ride on either both right- or left-side wheels.
bikini top 1. A soft top that covers only the front seats and leaves the rear uncovered. 2. What many of us like our significant others to wear on the trail.
bellhousing Bell-shaped enclosure for the clutch and flywheel on a manual transmission or the flexplate and torque converter on an automatic transmission.
billet A part machined from a single piece of metal, not a casting.
bleed 1. To remove air in a hydraulic system by pumping out fluid. 2. What hands often do while working on trucks.
blip Quick touch of the throttle to momentarily rev an engine.
blower 1. Supercharger. 2. Ventilation system's motor.
blown engine 1. A seriously damaged engine. 2. A supercharged engine.
blow the doors off To defeat a competitor during a speed contest.
blueprint To rebuild an engine to its OE design specs, machining and checking the weight, size, and fit of each component against a factory blueprint.
bobbed The rear of the truck, SUV, of Jeep has been shortened, usually adjusted for better departure angle.
body roll 1. Tendency of a truck's body and chassis to lean toward the outside of a turn as the result of cornering forces. 2. The flesh that protrudes over our beltlines.
bog 1. Running an engine below its intended operating range by driving in too high of a gear for the speed or load. 2. The mud pit at a mud-bog race.
bogger 1. A vehicle built for mud racing. 2. One who mud-races. 3. (cap.) Type of tire
boiling the balonies Spinning the tires.
bolt-on Aftermarket part or component that can be installed without special modifications or major disassembly.
boneyard 1. Wrecking yard, junkyard, salvage yard. 2. The Back 40 of many 4x4 owner's homes.
boost The increase in intake pressure above atmospheric pressure provided by a supercharger or turbocharger. Boost is measured in psi.
bore 1. The diameter of a cylinder. 1. The act of machining a cylinder to fit larger pistons.
bored-and-stroked Combination of an enlarged cylinder bore and a lengthened piston stroke, resulting in an increase in overall engine displacement and power; rarely boring.
bottom end 1. The crankshaft, connecting rods, and main bearings of an engine. 2. Power at low engine speed.
bottom-out When the truck's suspension is fully compressed and its bumpstops won't allow further suspension travel.
boxed Strengthen a frame by adding a metal plate to an open-channel framerail or crossmember, thereby turning a three-sided framerail into a four-sided rail.
brake fade A loss of braking power, the result of the brakes' friction surface or the brake fluid becoming overheated.
broach to pierce or open, sometimes referring to a splined cut on a gear or flange.
bulletproof An allegedly indestructible truck or component.
bump 1. A horizontal obstacle. 2. To blip the accelerator. 3. To back off an obstacle, then hit it again with momentum.
bumpsteer A situation in which the steering jerks when a truck encounters a bump in the road. Bumpsteer is often caused by improper steering geometry.
bumpstick Camshaft
bumpstop Rubber or urethane block used to limit suspension compression travel.
burnout Deliberate spinning of the rear tires to heat and clean the tires' tread in preparation of maximum acceleration from a standing start. Can also be used to impress onlookers.
butt-scratcher A trail obstacle that scrapes on a truck's rear end.

cam 1. An eccentric device which converts rotating motion to reciprocating movement 2. Camshaft.
camber The tilt of the front tires toward or away from the center of the truck relative to vertical. When the top of the tire leans out the camber is positive; if the tire leans inward, camber is negative.
cam duration Amount of time, expressed in degrees of crankshaft rotation, that a cam holds open the intake or exhaust valves.
cam lift Distance, expressed in thousandths of an inch, at which a cam opens the valves.
candlepower A light brightness rating. Not all manufacturers use the same method to determine candlepower.
caster The fore or aft tilt of the steering axis relative to vertical. Lifting a truck can cause too much negative caster, which results in wandering.
catalytic converter An emissions-control device that routes exhaust gases through an oval-shaped canister filled with palladium and platinum pellets, thereby converting the toxic exhaust gases to water vapor, carbon dioxide, and less-toxic gases. Syn. cat.
CB Citizens band radio. A two-way radio commonly used for communication between trucks on the trail.
center disconnect A four-wheel-drive system that engages the front axles at an inboard location rather than the outboard hubs.
center of gravity The theoretical center of mass in a vehicle. It can change dramatically due to passenger load and cargo.
cherry Clean, in unusually fine shape.
CFM Cubic feet per minute, generally used to measure airflow through a port, intake manifold, or carburetor; a system used to determine carburetor and fuel-injection capacity.
chaindrive A system in which a chain and sprockets drive gears instead of the gears being meshed together.
chick-deflector Repulsively ugly vehicle. Ant. chick magnet
chicken-handle A handle for passengers to grab when the going gets rough; also known by other, unprintable names.
chip A computer's microprocessor, computer. A nick in the paint.
chirp the tires To shift quickly during hard acceleration so that the tires momentarily lose traction.
chunk 1. Slang for the ring-and-pinion gear assembly inside a differential housing. 2. When parts eject from their functional location.
clip A truck's entire front sheetmetal section, including the fenders, hood, and cowl.
coilover A suspension that uses shocks with an integral coil surrounding the shock body, often used with custom-fabricated multilink suspensions because they offer the advantages of easy preload and ride-height adjustments, lots of wheel travel, and accurate spring dampening rates.
collector Device that collects exhaust gases from the exhaust manifold's (or header's) primary tubes and routes them into a single-exhaust pipe.
combustion chamber A cavity within the cylinder head(s), just above the piston(s), where combustion takes place.
compression ratio The ratio of cylinder volume with the piston at BDC to the volume remaining in the cylinder chamber when the piston reaches TDC. The greater the difference, the higher the compression ratio, generally producing more power. If the compression ratio is too high, however, it can cause detonation and an increase in pollutants.
contact patch Portion of a tire tread in contact with the road surface.
Cornbinder Slang for any 4x4 made by InternationalHarvester because the company is known for making farm equipment. Syn. 'Binder.
crank it 1. To turn the steering wheel hard left or right. 2. To start the engine.
crankshaft Shaft with large, U-shaped cranks that are connected to the pistons' connecting rods and transforms the pistons' reciprocal motion to a rotational motion, which powers the drivetrain. Syn. crank.
crawl-ratio The lowest gear ratio in the truck, found by multiplying the First gear ratio of the tranny by the low-range gear ratio of the transfer case by the axle gear ratio.
cross-drilled crank Crankshaft with additional lubrication holes drilled opposite the existing main journal oil feed holes, providing improved high-rpm-bearing lubrication.
curb weight Total weight of a truck with the fuel tank full, the engine oil at its proper level, and the cooling system full, but without a payload or passengers.
CV joint Constant velocity joint, two U-joints in tandem or a Rzeppa joint which allows for increased angularity of driveline components. Commonly found on front driveshafts and front-drive axles.
cylinder head The part of an engine that contains the valvetrain and the combustion chambers and covers the tops of the cylinders and pistons.

deck The surface of the engine block on which the head gasket and cylinder sit.
degreeing a cam Using a dial indicator and a degree wheel to verify that a cam's lift and duration is accurate.
departure angle The maximum angle a truck can descend before hitting the rear bumper or other components located behind the rear tires.
Detroit Locker A popular brand of automatic locking differential.
dial-in 1. To set up a truck's engine, chassis, drivetrain, stereo, or other system so that maximum performance results. 2. To set up a mechanical component for trouble-free operation.
direct ignition system Ignition system that has no distributor; ignition is sent directly from the multiple modulators (coils to the spark plugs).
directional tire Tire with an asymmetrical tread that is designed to produce superior traction when rotating in one direction only.
double-line A type of winch rigging that runs the cable to an anchor point and back to the vehicle, thereby doubling the pulling power.
Double-pumper A four-barrel Holley carburetor with mechanical linkage to open both the primary and secondary barrels and mechanical accelerator pumps in both the primary and secondaries.
drag link Steering link that connects the pitman arm to the steering arm.
droop Any downward suspension travel.
drop the hammer To accelerate rapidly from a stop.
dropped pitman arm An offset arm that lessens the angle between the steering box and drag link.
dualie A truck that has dual rear tires on each side.
dual plane An intake manifold with runners that do not share a common plenum, usually designed for low- to midrange engine performance.
dyno Abbreviation for dynamometer, a machine used to measure engine torque either at the flywheel (engine dyno) or rear tires (chassis dyno).

ECU Electronic Control Unit, computer unit for engine management.
EFI Electronic Fuel Injection; computer-controlled fuel delivery system.
EGR Exhaust Gas Recirculation, an emissions-controlled device that reintroduces burned exhaust gases to an engine's combustion chamber.
electronic ignition Ignition system that uses transistorized circuits instead of breaker points.
E.O. Number Executive Order Number, the number assigned to a part by the California Air Resources Board when it becomes legal to use on emissions-controlled vehicles.
exhaust backpressure Resistance to the free flow of exhaust gases through an exhaust system
exhaust headers Performance exhaust manifold built from equal-length steel tubes that is designed to speed the flow of exhaust gases exiting the cylinder head(s).
exhaust manifold Tubular cast-iron component that routes exhaust gases from the cylinders to the exhaust system.

fairlead A steel guide installed onto a winch mount to help direct the winch cable. Fairleads come in two styles: roller, which uses steel rollers, or Hawse, which features a simple bracket with large radiused edges for the cable to ride against.
fan clutch Thermostatically controlled clutch device that engages or disengages a mechanical radiator cooling fan according to the engine's cooling needs.
flathead An early engine design that located the valves in the block beside the cylinders, rather than the head (overhead valves) as is currently done.
flat spot Momentary decrease in engine power at some point within the powerband.
flat-top 1. A piston without a dish or a dome. 2. A popular '50s haircut.
forced induction Supercharged or turbocharged
four-banger A four-cylinder engine.
four-bolt main A crankshaft's main bearing caps held in place by four bolts.
freewheeling When the front hubs are unlocked and the wheels spin because of momentum rather than power.
fuelie Old slang referring to a fuel-injected engine or vehicle.
fuel injector Electromechanical device that squirts fuel into an engine.
full-floater An axle assembly designed to hold the weight of the vehicle on the axlehousing instead of on the axleshafts; has bearings at both the differential and wheel ends.

gas shock Damper shock absorber with two separate compartments, one containing hydraulic fluid, one containing nitrogen gas. The gas keeps pressure on a flexible, in some cases, moveable separating disc, that, in turn, keeps pressure on the fluid, thereby reducing the fluid's tendency to foam during aggressive driving.
g-force Measurement of the force generated during cornering, acceleration, or deceleration, expressed in units of gravity.
glasspacks Tubular style of muffler that uses fiberglass packing to absorb sound.
gnarly A difficult portion of a trail that may or may not make you nervous. Syn. exceptional.
granny gear An extremely low First gear in a manual transmission. For example, an SM465 has a 6.55:1 First gear ratio.
grenade Catastrophic failure of an expensive part. Engines, transmissions, and axle assemblies can all grenade.
greenhouse Upper portion of a truck's body; the structure above the beltline, including the roof, windows, and pillars. Syn. office.
ground effect Reduced airflow under a truck provided by an air dam and side skirts. Less pressure underneath a truck allows the air passing over its top to push downward, thus creating an improved grip on the road as well as improved top speed and fuel efficiency. Impedes ground clearance in 4x4s.
gumbo Deep, sticky mud.
gun it To deliberately rev an engine.
gusset Triangular metal support used to add strength; is welded in place where two framerails connect or where two tubes of a rollcage are welded together.
GVWR Gross Vehicle Weight Rating, the combined weight of a vehicle and its rated cargo capacity.

halogen light High-output headlight or driving light that has halogen gas inside the bulb. When surrounded by a halogen gas, the bulb's tungsten filament can carry a higher current, thus producing a more brilliant white light.
hammered 1. A truck that's thoroughly destroyed. 2. A truck that has a chopped top or a severely lowered suspension.
handle The nickname you use on the CB.
H.E.I. High-Energy Ignition, a powerful and reliable GM distributor assembly with a self-contained coil.
Heliarc welding A form of tungsten inert gas welding used primarily on aluminum and stainless steel.
Helicoil Stripped thread repair system, consisting of small coil-spring inserts that thread into place on damaged female screw threads.
high-centered When a truck is firmly stuck, usually caught on its frame on an obstacle unable to move.
high-pinion See reverse-rotation.
hi-Po High-performance.
hole shot Beating a competitor at the start of a race; coming off of a dead stop quicker; coming out of the hole quicker.
hook up 1. To gain traction. 2. To gain a date.
hub Wheel mounting surface.
huffer A beltdriven supercharger.
hydraulic'd Past tense only, said of an engine that has been submerged in water and has sucked water into its cylinders through the intake and will no longer rotate because the pistons moving up the cylinders cannot compress the water.

IFS Independent Front Suspension, a type of suspension system that allows the two tires on one axlehousing to move separately from one another.
intake ports Passages within a cylinder head that route air and fuel to the intake valves.

juicebox An automatic transmission.

kick-down Quick downshift on an automatic transmission when the engine is given full throttle.
kicker shocks Shocks mounted in a near horizontal position between the axlehousing and the leaf springs. Kicker shocks are valved with a high rate of compression damping and are intended to reduce axlewrap.
kick-up Section of a frame that is curved up to clear an axlehousing.

ladder bars Longitudinal suspension control arms that connect the axle to the frame, preventing axle wind-up and hop.
lash Amount of clearance between a valve and a rocker arm or between a rocker arm and a lifter or pushrod.
lateral link Tubular suspension rod that positions the axlehousing so that side-to-side movement is minimized during cornering.
LED Light-emitting diode, a small semiconductor that lights up when current is passed through it. Used on some dashboard displays and taillights.
lifted Any 4x4 that is raised either by a suspension or body lift.
lift-block A spacer placed between the axle assembly and the springs to lift a truck inexpensively. These are only safe on rear-axle assemblies.
light it off Start an engine.
limited-slip differential Final-drive system where the two axleshafts are mechanically connected with a series of clutchlike plates to prevent wheelspin on slippery surfaces and to ensure that the engine's power is transmitted equally between the two tires.
line A driver-selected path that gives a truck the best route to climb over an obstacle or through a pathway. Choosing the right line is essential to successful four-wheeling.
locked in To have engaged the manual front hubs into the lock position.
locker A device in either the front or rear differential that sends engine power to both wheels regardless of traction.
lockers front and rear One of the most common truck-owner fibs.
Loctite A product used on fasteners to maintain torque.
long-block Engine assembly consisting of a cylinder block, a crankshaft, a camshaft, bearings, pistons and rings, connecting rods, an oil pump, an oil pan, a timing cover, seals, cylinder heads, and an intake manifold.
loud pedal Accelerator.
low gears Gears that increase the amount of reduction in the transmission, transfer case, or axle. In an axle, they are expressed as the ratio of ring-gear teeth to pinion teeth, so low gears are numerically higher than high gears. (Example: 4.10 gears are lower than 3.55 gears.) Rockcrawlers typically have low gears.
low-lock To have the transfer case in 4-Lo therefore locking out the center differential, if so equipped.

mandrel bend Hydraulic or mechanical tube-bending machine that uses dies and mandrels (forms) to bend tubing in such a manner that the walls don't collapse.
manifold cooking To use a hot intake manifold as a heat source for cooking on the trail. Burritos and cans of beans or chili are favorite manifold delicacies.
MAS Mass Airflow Sensor, a device that measures the amount of airflow into the intake manifold. This information, as well as data from other sensors, is sent to the engine's computer, which calibrates the optimum air (fuel and adjusts the EFI system as required.
meats Tires, particularly large, aggressively treaded ones. Syn. skins, shoes.
MIG welding Metal Inert Gas welding is a wire-feed welding system that uses argon gas as a shielding agent for the weld. Steel, stainless steel, aluminum, and other metals are commonly welded with a MIG welder.
mill 1. Engine 2. Milling machine.
modular wheel Custom or racing wheel with an inner, an outer, and a centersection that are bolted or riveted together.
monochrome Styling inspired by European performance cars where the bumpers, grille, body trim, and door handles are painted the same color as the body.
mountain motor Big-block engine, typically bored and stroked to at least 500 cubic inches.
Mouse motor Chevy small-block V-8 engine, named Mouse because of its small overall physical size, and because, some say, GM executives wanted to scare Chrysler's "elephant" Hemi engine with the new, powerful small-block Chevy.
Multilink Solid-axle suspension design where coil springs are used instead of leaf springs, and the axle is located by longitudinal and lateral suspension control arms, or links.

nail it To apply full throttle.
negative offset When the wheel's mounting surface is outboard of its centerline.
normally aspirated An engine that relies on vacuum through its intake manifold and cylinders to draw in an air-fuel mixture; an engine without a forced-induction supercharger or turbocharger.
NOS 1. New old stock; original equipment, unused parts for vintage trucks, often found in their factory cartons at dealerships. Ant. repro, reproduction. 2. A nitrous oxide injection company. 3. Slang for nitrous.

OEM Original equipment manufacturer. Syn. stock.
off-camber A situation in which the truck is sideways on an incline, increasing the likelihood of a rollover.
oil gallery Small passages within the engine block and cylinder heads through which lubricating oil circulates.
one-off 1. Custom part or component that is fabricated from plans; no other identical copy exists. 2. Wide-production modifications to an existing vehicle, such as a Saleen Explorer.
out to lunch Worthless, a truck that doesn't run well or look right.
oversteer Cornering condition where the rear tires slide toward the outside of the turn.

Panhard rod A transverse link (rod that attaches to the truck's frame at one end and to the axlehousing at the opposite end), providing lateral positioning of the axlehousing relative to the chassis.
paperweight A part that's broken beyond repair can be used as an excellent paperweight.
payload Maximum weight a truck can carry, calculated by subtracting the curb weight of the truck and a 150-pound allowance for each passenger from the gross vehicle weight rating.
peg-leg An open differential. Syn. one-legger.
pickle fork Fork-like tool used to separate suspension components, such as ball joints and tie-rod ends, for repair.
pinion angle The angle of the pinion yoke on an axlehousing in relation to its driveshaft.
pitman arm Steering lever that converts the rotary motion of the steering box to the linear motion of the steering system's centerlink.
plenum Box or cavity at the intake manifold's entrance that stores the air/fuel mix for distribution to the intake runners.
plow Understeer.
port injection Electronic fuel-injection system that injects fuel directly into the cylinder-head ports.
posi Short for Posi-traction, a limited-slip differential used by General Motors. The term is often used generically for any limited-slip device.
positive offset When the wheel's mounting surface is inboard of its centerline.
prerunner An off-road truck that's built to prerun a desert race course so that the driver can study and practice on the course before the race.
progressive-rate springs Suspension springs that become progressively stiffer as they are compressed.
proportioning valve Hydraulic braking valve that varies the braking force at the front or rear wheels, depending on pedal pressure, load, and weight transfer, to reduce or eliminate wheel lockup.
P.T.O. Power take-off, an accessory powered by engine output, usually a winch.
pumpkin The centersection of an axlehousing that contains the differential carrier and gearset. Syn. coconut, third member.
pushrod Thin metal rods that transmit the motion from the camshaft and lifters to the rocker arms, and thus operate the valves on an overhead-valve (OHV) engine.

quad 1. Four-barrel carburetor. 2. A four-wheeled all-terrain vehicle.
quarter-panel Body shop term for the front or rear corner sheetmetal assembly.

radius arms Brackets used by Ford that locate the front axlehousing on coil-spring suspensions. Dodge and Jeep use similar brackets. Syn. trailing or control arms.
rack-and-pinion A steering system that uses a pinion gear at the end of the steering shaft to engage a horizontal-toothed bar, the rack, which is attached to the tie rods and the steering knuckles.
rake When the frontend of a truck sits lower than the rear.
ramp breakover angle The angle formed by lines drawn from the front and rear tires' contact patches and the midpoint of the wheelbase on the chassis; the greater the angle, the less likelihood of high-centering.
Rat Chevy big-block V-8 engines, normally offered in 396ci, 402ci, 427ci, and 454ci sizes. Named because it was a large companion to Chevrolet's small-block Mouse V-8.
rebound After a suspension spring is compressed by a bump, the spring naturally tries to return to its previous length, extending the suspension upward toward its original ride height.
recirculating ball steering Steering assembly that uses a worm gear on the end of the steering shaft to turn a sector gear that is within the steering box and attached to the pitman arm. Ball bearings are used between the worm and sector gears for smooth operation.
redline Absolute maximum engine speed, expressed in rpm, at which an engine can/should be operated; indicated by a red line on the tachometer. Syn. rev limit.
repro Aftermarket reproduction parts, manufactured to appear, fit, and function as originals. Not the same as OE or N.O.S., which are both factory-issued parts.
restify To build a truck that is basically restored but has been updated with modern convenience and performance enhancements.
retrofit Installing new parts or systems on an older truck for the purpose of upgrading, such as retrofitting a modern fuel-injection system in place of the original carburetor.
rev limiter An adjustable electronic device that restricts engine rpm to a predetermined limit so engine damage does not occur.
reverse-rotation Refers to an axle design where the pinion is positioned above the axle centerline.
ring-and-pinion Gearset that drives the wheels; the pinion is a gear attached to the rear of the driveshaft, and the ring gear is part of the differential that turns the axles.
rock magnet A low-hanging component of a 4x4, such as a ladder bar, that seems to catch on every obstacle.
rock massaging Body damage caused by rocks and other obstacles on the trail.
rocker arm Pivoting valvetrain levers. One end of an engine's rocker arms are moved by the pushrods/lifters and the opposite end's open intake or exhaust valves.
rocker panel The sheetmetal section of a truck's body located below the doors and between the front and rear wheel openings.
Roots supercharger Positive-displacement, beltdriven supercharger; originally designed in 1859 by Francis Roots for use as a water pump.
RTI Ramp travel index, a measurement of suspension flexibility and articulation that's calculated by dividing the distance the hub's centerline travels up a (usually 20-degree) ramp by the vehicle's wheelbase in inches, multiplied by 1,000.

sanitary Well designed, engineered, and constructed; cleanly built; superior mechanical workmanship. Syn. sano.
semi-floater An axle assembly that carries the weight of the vehicle on the axleshafts. These are typically weaker than full-floaters.
serpentine belt Engine accessory drivebelt that is long and follows a snaking path while driving the alternator, water pump, A/C unit, and power-steering pulleys.
shackle Connector between the rear of a leaf-spring pack and the frame; allows the spring to lengthen as the suspension is compressed.
shift kit Package of high-performance components for an automatic transmission that firms the shifts, alters the shift points, and improves overall performance.
shiny-side down When a truck rolls over. Syn. rubber-side up.
short-block An engine block that has a complete bottom end, including the crankshaft, rods, pistons, and camshaft, but without the cylinder heads, intake and exhaust manifolds, water pump, and other accessories.
sidehill A portion of a trail that leads across a steep hill instead of up or down. See off-camber.
single-plane manifold Intake manifold with a single plenum feeding all of the engine's intake runners.
skin Body sheetmetal.
skins Tires.
slickrock A type of sandstone dominant in Moab, Utah. Slickrock actually isn't slick and provides excellent traction.
slushbox An automatic transmission. Syn. juicebox.
small-block A V-8 engine typically having 400 or less cubic inches of displacement.
snatch-block A pulley device used in assisting with getting unstuck; it doubles as a winch cable's pulling power.
snatch strap A thick nylon strap used to pull out stuck vehicles. Syn. tow strap, yank strap.
spool out To pull the winch cable off the drum after releasing the brake.
spotter A codriver who helps guide the driver over obstacles, often using hand signals.
spring rate The force required to deflect a spring 1 inch, expressed in pounds per inch of spring compression or deflection. The higher the per-inch spring rate, the stiffer the spring.
spun bearing A bearing that is either worn or frozen and has rotated in its retainer. In an engine, this causes the bearing to block off its oil passage and results in major damage.
stair-step An obstacle that contains one or more ledges that must be climbed in succession. Stair steps are common on trails that follow washes or creek beds.
stand on it Full-throttle acceleration.
swamped To drown the engine; to drown the entire truck.
synthetic oil Manmade lubricants; they generally have a greater capacity to lubricate and resist heat than standard mineral oil.

tachometer Device used to measure and display engine speed, expressed in revolutions per minute. Syn. tach.
tack welds Series of small welds, spaced approximately 1 inch apart, which are used to hold together two pieces of metal until the final welding can be performed.
taco'd Axlehousings, frames, or other components that have been severely bent, usually from jumping the truck.
tail gunner The last vehicle/driver on a trail ride. The tail gunner is responsible for making sure everyone completes the trail.
tall gears The opposite of low gears, they are represented in ratios that are numerically lower than "low" gears; e.g., 3.08s are taller than 4.10s.
TBI Throttle-body fuel injection.
threshold braking Applying as much pressure to the brake pedal as possible without going to wheel lockup.
throwout bearing On a clutch assembly, a shaft-mounted bearing that is moved from pressure on the clutch pedal and disengages the clutch disc from the engine.
T-case Transfer case.
tie rod Steering linkage between the pitman or idler arm and a steering arm that moves the steering knuckles.
TIG welding Tungsten Inert Gas welding, also referred to as heliarc welding, usually used for joining aluminum and stainless steel.
timing chain/gears Chain or gears that transmit rotation from the crankshaft to the camshaft.
toe-in, toe-out Inclination of a pair of front wheels slightly inward or outward as viewed from the truck's front.
torque converter Fluid coupling between the engine and the automatic transmission. The engine powers a fan-shaped impeller inside the torque converter, which splashes oil onto a turbine (another fan-shaped device), and the turbine transmits its power to the transmission's gearbox.
torsion bar Suspension spring that looks like a long metal rod. One end is attached to the truck's frame, and the other end is attached to the suspension's A-arm. When the A-arm moves, the torsion bar is twisted and then springs back to its original shape, thus its springing action.
TPI Tuned-port fuel injection.
trail boss The leader of a trail ride.
trailer queen A vehicle that's built primarily for show and is trailered to events.
TTB Twin-Traction Beam, a type of Ford front suspension that utilizes an axle assembly with pivot points, allowing the tires to move independently.
tunnel ram Intake manifold with a large plenum and long, straight runners, used for high-rpm engines.
turned turtle A truck that's rolled upside down.
two-bolt main Engine block with its main crankshaft caps held in place by two bolts.
two-wheeling When tires lift off the ground during a tricky maneuver. Syn. bicycling.

U-bolt U-shaped bolt commonly used to attach an axlehousing to a leaf-spring pack.
U-joint Mechanical joint that can transmit rotary motion while swiveling. Used at both ends of a driveshaft to transmit power from the transfer case to the differential.
understeer Cornering condition where a truck's front tires lose grip before the rear tires, causing the front end to slide or push toward the outside of the corner.
unglued 1. Damaged or destroyed; a blown-up engine has become unglued. 2. The codriver's mental state following a rollover.

vacuum advance Device that advances or retards ignition timing according to the degree of engine vacuum. At low engine speed, there is plenty of engine vacuum, so the ignition is advanced; at wide-open throttle, there is little vacuum, so the ignition remains at its original timing advance.
vacuum secondaries Secondary carburetor barrels that are pulled open by engine vacuum.
valve lift Circular, stemmed device used to control the airflow in and out of an engine; operated by the camshaft/pushrods/rocker arms.
valvetrain The valve lifters, pushrods, rocker arms, and valve springs.
vaporlock Condition where fuel boils within the fuel line or carburetor, causing bubbles to form that impede the fuel flow or cause excessive fuel to flood the carburetor.
variable-ratio steering Power-steering box that varies the steering ratio. At low speeds, the steering response is quicker for maneuverability; at high speeds, the steering ratio is reduced for stability.
ventilate the block To throw a connecting rod through the side of an engine block due to component failure or excessive revs.
venturi Carburetor barrel or throat with a slightly narrowed or hourglass shape to its interior. The small, narrowed area speeds up airflow and helps pull the fuel past the carburetor jets and into the air stream.
VIN Vehicle identification number, a serial number that identifies a vehicle.

wail To perform at peak power or efficiency.
wheel adapter Metal plate with wheel studs that allows a wheel with one bolt pattern to be used on a truck with a dissimilar bolt pattern.
wheelbase Distance from the center of a truck's front wheel to the center of the rear wheel on the same side.
wheel travel The total distance a wheel can move up and down; affected by suspension travel and wheelwell clearance. More wheel travel means a more flexible suspension and more potential traction.
white-knuckle An obstacle that is scary enough to make the driver grip the steering wheel extremely tight.
windage tray An internal engine shield, mounted close to the crankshaft and intended to deflect oil away from the crank as it rotates.
wiring harness Major part of a truck's electrical wiring system; a group of wires bundled together.
WOT Wide Open Throttle.
wrist pin Hollow metal tubular pin that attaches the piston to the connecting rod.

zerk fitting Nipplelike fitting on suspension and chassis parts and on U-joints, through which lubricant is pumped under pressure to lubricate the components' internals.

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