4x2: four wheels, two driven.
4x4: four wheels, all driven or drivable,
4x4, 6x6 etc.
6x6: six wheels, all driven or drivable
ABS: Anti-Lock Braking system, but ABS is
actually an abbreviation for Anti Blockier System a Wabco
Gmbh patent, Experience.
ACE: Active Cornering Enhancement, a BMW
/ Rover-ism ~ 1997, electronic system automatically manipulates
suspension and/or brakes to assist cornering; also see ESP.
ADR: Australian Design Rules; it is important
to check ADR's if carrying out vehicle modifications.
All Wheel Drive: Taken literally AWD means
all four wheels can be driven, but there is some ambiguity
as to just what "driven" means. If a centre diff'
is used between the front and rear axles then all wheels
share equal torque (unless one slips and an LSD or diff'
lock takes over). A cheaper arrangement is to drive one
axle via a viscous coupling or similar. In this case one
axle receives no torque until the other axle slips - is
this all wheel drive? Debatable.
Anti-Roll Bar: torsion bar between left
and right ends of an axle - it increases roll-stiffness
which can improve on-road handling but can also restrict
Approach Angle: the angle at which a line
drawn from the leading part of the vehicle's bodywork and
touching the front tyre meets the ground. It gives an indication
of the steepness of a step-up that a 4x4 can approach without
its nose digging in. The bigger the angle, the closer it
is to 90 degrees the better for offroad work. See also [web
page] and departure angle.
ATV: All Terrain Vehicle, often very basic,
possibly with skid-steering, balloon tyres, no suspension.
AWD: All Wheel Drive.
Back-lash: the free-play between gears -
a certain amount of backlash is essential.
BAS: Brake Assist System (Mercedes Benz,
1990s), electronics detect sudden application of brakes
and increase braking effect under the assumption that this
is, or should be, a panic stop.
Boge Self-Levelling Unit: a self-contained
unit which uses suspension movements to pressurize itself
and so level the suspension under heavy load - as fitted
to the Range Rover (Classic).
Capstan: type of winch.
Carawagon: (ex-) British firm that did camper
conversions, esp' on Land Rovers and even Range Rovers.
Centre Differential: incorporated in the
transfer case of a full-time 4WD vehicle to allow the front
and rear axles to rotate at different speeds during cornering
- is pioneered in the 1902 Spyker 4WD.
Champ: Austin Champ, British military four wheel drive see
CJ: Civilian Jeep.
Crew-Cab: body configuration, two rows of
seats and generally four doors, also fitted with a tray
(ute). Also known as double-cab.
Cross-Axle Diff' Lock: a differential lock
in an axle differential, ie. it makes the half-shafts rotate
at the same speed.
CV Joint: Constant Velocity joint, used
in drive-shafts where the input and output shaft must rotate
smoothly at the same uniform speed of rotation.
CVT: Continuously Variable Transmission,
e.g. [web page].
Dakar: city on the Atlantic coast of Senegal,
finish of the Paris - Dakar, lately Granada - Dakar, offroad
rally. (The start of the 2000 Dakar - Cairo rally.)
Dead Axle: uses a tube (or beam) to connect
wheels but the tube does not contain a differential or half
shafts. Drive is delivered to the wheels by separate half-shafts
fitted with universal joints or cv joints.
Departure Angle: the angle at which a line
drawn from a vehicle's rearmost bodywork and touching a
rear tyre meets the ground. It gives an indication of the
maximum steepness of a step-down that a vehicle can negotiate
without dragging the rear bodywork. Long body overhangs
reduce the departure angle. The closer the angle is to 90
degrees the better for offroad work. See also approach angle.
Differential: has one input and two outputs,
e.g. allows left and right wheels on an axle to revolve
at different speeds during cornering.
Differential Lock: dog-clutch, prevents
differential action e.g. in slippery conditions. See [web
Direct Injection: where fuel is injected
directly into the (main) cylinders of an engine, esp' in
diesels or very rarely in petrol engines; more efficient
than indirect injection where diesel is injected into a
small chamber off the main cylinder.
DOHC: Double Overhead Cam Shafts (two per
bank in a V-engine) enable valves to be further separated
than with a single camshaft (SOHC), allowing valves to be
larger and/or better placed, giving more power.
Dormobile: British firm carried out camper
conversions including pop-top roofs, often on 4x2 vans,
notably Bedfords, but also on four wheel drives.
DUKW: large [amphibious] military 6x6 vehicle
dating from WWII.
ECU: Electronic Control Unit - heart of
the engine management system of a modern car.
Efi: Electronic Fuel Injection.
ESP: Electronic Stability Program, a Mercedes-Benz-ism
from the late 1990s, e.g. on the Mclass - electronics manipulate
the brakes and engine torque to prevent or reduce skids;
also see ACE.
F-Head: see IOEV.
FC: Forward-Control or cab-over design,
with the cab over the engine and front wheels - makes for
a larger load space. [Example.]
Four Wheel Drive: Taken literally 4WD means
four wheels, all of which are (or can) be driven. See full
time and part time 4WD.
Full Time 4WD: all four (or more) wheels
are driven at all times. Strictly, a centre diff' should
be employed to share equal torque to front and rear axles,
but see `all wheel drive'.
Fully Floating Axle: this is nothing to
do with amphibious vehicles, rather it refers to a fully
floating half-shaft in a live axle. In a F.F. axle, the
wheel hub is fully supported by twin taper roller bearings.
The half shaft therefore only transmits torque from the
differential to the hub. If the half shaft breaks, the wheel
won't fall off!
FWD: Four Wheel Drive Auto Co (1911-).
Gipsy: Austin Gipsy (UK).
GPA: General purpose amphibious, the amphibious
Jeep or Seep; built by Ford.
GPW: WWII Jeeps as built by Ford.
Green Laning: following (British) public
rights of way, or green lanes, in a four wheel drive vehicle.
Haflinger: small 4WD (was) made by Steyr
HDC: Hill Descent Control, electronic system
applies brakes automatically to crawl down a steep hill,
as on the Freelander, ~ 1997.
HMMWV: High Mobility Multi-purpose Wheeled
Vehicle, aka [Hummer] or HumVee.
Hookes Joint: universal joint.
Hub Reduction Gears: reduction gears in
the hub carrier, often used in conjunction with a portal
Hummer or Humvee: see HMMWV.
Hydraulic Lifter: self-adjusting tappet,
uses oil-pressure and one-way valve to control the backlash
between cam-shaft and engine valves (as opposed to solid
Hydraulic Stall: if water is drawn into
the engine cylinders, e.g. during wading, it will stop the
engine immediately, often bending the con-rods, because
water is incompressible.
Indirect Injection: where fuel is injected
into a small combustion chamber that leads off the main
cylinder in an engine - especially in (some) diesel engines.
Intercooler: a small radiator used to lower
the temperature of air compressed by a turbo-charger (or
super-charger). This increases its density, so more air
can enter the cylinders - more power.
IOEV: Inlet Over Exhaust Valve - the inlet
valve is in the cylinder head but the exhaust valve is in
the block, e.g. Willys CJ3B Jeep F-head, or Land-Rover Series
Jeep: The term was first applied to a vehicle
in the form of the WWII Jeep MB.
Kinetic Recovery: the use of momentum and
a snatch strap to extricate a bogged vehicle. See [web page].
LandCruiser: 4x4 by Toyota.
Live Axle: uses a rigid axle tube. Half-shafts
pass down centre of tube (cf dead axle). This system is
strong and simple, and ground clearance does not reduce
under braking, but it has more unsprung weight than independent
suspension. See [web page].
Locker: replaces the planet and side-gears
in a diff', torque goes to the non-slipping wheel, may give
"twitchy" handling. See [web page].
LPG: Liquified Petroleum Gas, butane, propane
and/or propylene compressed. Popular dual-fuel conversion
for large petrol cars and four wheel drives because LPG
is very cheap in Australia, 20c to 25c/L v. 70c to 75c/L
(1997). Power is slightly reduced. Those engines susceptible
to burning valves should perhaps not be converted.
LSD: Limited Slip Differential See [web
LWB: Long Wheel Base, usually counting anything
over 100" (2540mm).
MA: Willys Overland MA, which developed
into the MB model, won the US army competition for what
came to be known as the Jeep, as described in the Rifkind
Military Vehicles: web page.
MPFI: see MPI.
MPI: Multi-Point Injection, Efi system where
fuel is injected into the intake of each cylinder rather
than at one point (throttle body injection) - allows more
precise fuel metering.
Mule: minimalist four wheel drive - M274
Mutt: Military Utility Tactical Truck M151
(they must do it deliberately). See [web page].
OHC: Over Head Camshaft, cam shaft is in
the head, above the valves.
OHV: Over Head Valves where the inlet and
outlet valves are in the cylinder head (in contrast to side-valves).
Valves are operated by push-rods from a cam-shaft at the
side of the engine.
Open Differential: a "normal"
differential without diff' lock or LSD features - axle looses
traction if one wheel slips.
Overdrive: a top gear that is higher than
1:1. Originally overdrives were only provided as optional
units bolted onto the original gearbox, and often employing
epicyclic gears. The term is now also applied to the top
(usually 5th) gear ratio in the main gearbox when it is
higher than 1:1.
Oversteer: tendency of a car to turn more
sharply than the driver intended, probably leading to a
rear wheel skid and eventually a spin, especially rear wheel
drive vehicles when too much acceleration is applied.
Panhard Rod: provides sideways location
of a live axle.
Part-Time 4WD: a vehicle that is normally
in two-wheel drive but one that can engage drive to the
other two wheels, usually through a dog-clutch.
Portal Axle: system where the half-shaft
enters the hub-carrier higher than the stub axle, thus raising
the diff' and half-shafts for extra ground clearance. Drive
is carried to the hub by gears. See Hummer, Pinzgauer or
PTO: Power Take Off, unit bolts onto transfer
case (usually), incorporates a dog clutch and is used to
drive a winch or other special equipment.
Quattro: A series of four wheel drive road
/ rally cars by Audi.
Ramp-Over Angle: The minimum internal angle
of an inverted-V ramp that a vehicle can drive over without
dragging its belly, ie. a measure of the sharpest bank it
can drive over. A typical figure is about 150 degrees; the
smaller the better offroad. NB. sometimes the ramp's `external
angle', 180-ROA, is given, typically a figure of about 30
degrees; subtract from 180 to convert. See [web page].
Register: a club that specialises in the
history and the restoration of vehicles, usually to original
RST-V: US Marines' plans for what is in
effect the Jeep for 2000+ - Reconnaissance, Surveillance
and Targeting Vehicle.
Scout: four wheel drive made by International
Seep: the [amphibious] Jeep, all based on
the Ford built Jeeps.
Series: the [SI-SIII] leaf-sprung Land-Rovers,
Side Valve: where the inlet and outlet valves
are in the cylinder block rather than the cylinder head
(OHV), e.g. as in the Willys Overland Jeep MB.
Snatch Strap: elastic strap used in kinetic
recovery. See [web page].
SOHC: Single Over-Head Cam, operates engine
valves. See DOHC, OHC.
Solid Lifter: Non self-adjusting (i.e. solid)
tappet, see Hydraulic lifter.
Speeding Ticket: Voluntary form of taxation.
Super-Charger: A turbine driven directly
by the engine to compress the engine intake air.
Sway bar: see anti-roll bar.
SWB: Short Wheel Base, usually counting
anything under 100" (2540mm).
Tirfor: Brand of hand-winch which pulls
the rope through it.
Torsen: Type of limited slip differential,
incorporates pairs of worm gears driving the side-gears.
Torsion Bar: Type of spring, rod or bar
twisted by suspension movement, esp' independent front suspension.
Transfer-Case: Secondary gearbox used to
transfer drive sideways so that it may then be carried forward,
around the engine, to the front diff' and axle. Usually
also provides high and low gear ratios.
Transmission Wind-Up: Stress in the transmission
system caused by wheels travelling different distances (e.g.
cornering) but unable to be relieved because diff' locks
are engaged or because part-time 4WD is engaged.
Trial: A four wheel drive competition on
a closed course that emphasises precise vehicle control
rather than outright speed.
Turbo-Charger: Exhaust gases drive a turbine
which drives a compressor which raises the engine air intake
pressure or charges the engine with more air - more power,
Tyre Dimensions are explained [here].
Understeer: Tendency of a car to turn less
sharply than the driver intended, especially a front wheel
drive vehicle under hard acceleration.
Unimog: All wheel drive trucks made by Mercedes
Benz See [web page].
Universal Joint: See [web page].
Viscous Coupling: An arrangement of discs
in a viscous fluid that allows two shafts to rotate at the
same or only slightly different speeds. It can be incorporated
in a differential to allow a slow, but not a high speed,
differential action, ie. preventing wheel-spin without transmission
wind-up. See [example]
Willys Overland: Makers of the WWII [Jeep].
Winch: Various kinds, see [examples].
Wishbone: A-frame component of independent