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Automotive
Encyclopedia
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L -
| L-head
engine |
An
engine design where the valves are located in the block next to the
cylinder. In such an arrangement, the combustion chamber protrudes
past the edge of the piston and forms the the shape of an L. Because
the valves are in the block, a low-profile or "flat" cylinder
head can be used. L-head engines are commonly referred to as Flatheads,
or side-valve engines. |
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| L-Jetronic
injection |
The
name of a Bosh fuel injection system that uses electromechanically
controlled fuel injectors and sensors. Fuel metering is done by controlling
the amount of time injectors are open. Sensors include an airflow
sensor and oxygen sensor. A refinement to this system is the LH-Jetronic
system which incorporates a air-mass sensor in place of an airflow
sensor. |
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| Ladder
frame |
A
frame made of two heavy-duty parallel steel rails with smaller connecting
members positioned transversely (shaped similar to a ladder). Used
widely in trucks and sport utility vehicles (SUV's) and on a few full-sized
cars. Although relatively heavy, a steel frame helps reduce noise
and vibrations transmitted to the passenger compartment. Replaced
by unitized chassis construction on most passenger cars. |
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| Ladder
rack |
A
metal or wood structure which can be bolted to top of vans or pickup
trucks to carry long objects such as a ladder. Pickup trucks used
for construction often have a structure that mounts to the truck's
bed and extends over it's hood. |
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| Laminar
flow |
An
aerodynamic term where the flow of air over a surface is predominately
parallel such as seen on wind tunnel demonstrations. Smooth parallel
airflow over a surface such as an automobile body is desired as
it indicates greater aerodynamic efficiency.
Also,
the smooth flow the air/fuel mixture through the intake ports of
an intake manifold and cylinder head.
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| Laminated
glass |
A
type of safety glass used on automotive windshields. Consists of two
sheets of glass with a clear plastic layer between which results in
a tougher, safer glass. If laminated glass is damaged, cracks tend
to appear locally. When damage is severe, the glass shatters but stays
adhered to the plastic lamination film. The film may stretch and flex
but resists puncturing and splintering. All vehicles sold in the U.S.
require the used of laminated glass windshields. Side and rear windows
use Tempered glass. See Tempered glass. |
| Landau
top |
Refers
to a formal automobile with a convertible top, or vinyl or cloth
top, which covers it's rear pillars and rear half of it's roof.
Originates from convertible carriages invented in the Bavarian town
of Landau (Germany) in the 18th century. The Landau carriage had
an enclosed, drop-center body and seated four occupants (two on
each side that faced each other), the driver was seated external
of the cabin. The carriage was designed for comfort and featured
a low step-in height and a leather convertible top that folded down
in two pieces (front and back) and latched in the center. The formal
landau carriages were used mainly for ceremonies such as weddings
and funerals and transporting notable guests. A Dress Landau had
a continuous curved design (not dropped) and were considered even
more formal and often used by nobility. Today they are a popular
style of carriage used for weddings and touring the downtown's of
many large cities.
Early
auto designers which were often former carriage designers adopted
the split-top design to the rear of early automobile roofs to make
them appear more luxurious. Landau bars (see below) appear on nearly
all modern day hearses. Also see Faux top, Convertible and Brougham.
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| Landau
bars |
Distinctive
formal trim pieces roughly shaped like an elongated "S"
found on the rear pillars of most hearses. Smaller Landau bars are
often positioned on the B-pillars or rear pillars of vinyl top-equipped
automobiles with an upper level trim package. A hold over from Landau
horse carriages produced in Germany in which externally positioned,
slightly curved bars served the function of holding up the retractable
soft top. The curved bars were a signature of the highly formal Landau
carriages. |
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| Lash |
Clearance
between two parts. The term lash is often used when describing the
play or clearance between valve stems and rocker arms. |
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| Latch |
A
mechanism mounted inside doors and under the hood and trunk which
secures hinged panels to the chassis. Doors and the hood use two-stage
latches for safety. The first stage latches the panel even when minimal
effort is used to close it. The second stage latches doors and the
hood when they are fully closed. Rods generally connect door handle
levers to the latches while a cable connects a handle to the hood
latch. Also see Striker. |
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| Lateral
acceleration |
The
outward pulling force on a vehicle as it negotiates a curve. Centrifugal
force acts on the vehicle and tries to pull it outward. At the same
time, tires develop an equal and opposite force which acts against
the road. Lateral acceleration is measured on a skid pad and expressed
in g's. On a skid pad, a car is driven around a 100-300ft circle as
fast as possible without skidding out of control. The steady-state
lateral acceleration of a vehicle can be calculated by knowing the
size of the circle and the time required to make a revolution. |
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| Lateral
arm/link |
The
name of the lower locating arm used in a MacPherson or Chapman strut
suspension system. The lateral link is positioned horizontally and
along with the strut helps maintain vertical wheel alignment. |
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| Lateral
runout |
Side-to-side
movement of a wheel or pulley as it rotates. Also referred to as Shimmy. |
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| Lateral
support |
A
characteristic of a car seat to restrain sideways forces exerted on
passengers during a curve. Bucket seats, especially those with protruding
side panels or hip cushions such as used on sports cars help prevent
occupants from sliding sideways during aggressive cornering maneuvers. |
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| LCD |
See
Liquid Crystal Display. |
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| Lead-free
gasoline |
Gasoline
that does not contain lead or any lead additives, now called Unleaded
Gasoline. Tetraethyl lead was added to gasoline to increase it's
octane rating and lower an engine's tendency to produce knock (detonation)
which can lead to engine damage. The lead also served to lubricate
valve seats. Because of health hazards associated with lead exposure
from automotive exhaust, lead additive levels were reduced, and ultimately
eliminated from U.S. gasoline during the 1970's-1980's. Some of the
side affects of the changeover were, detuned engines (compression
ratios needed to be reduced), accelerated valve seat wear and problems
with detonation and run-on. High-octane gasolines, hardened valve
seats and electronic engine controls have increased engine output
more than compensating for the switch to unleaded gasoline. |
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| Leading
arm |
A
suspension arm that connects on one end to the wheel's mount and to
the vehicle's chassis on the other end and allows the wheel to pivot
up and down. Leading arms lay horizontal and parallel to the vehicle
and rearward of the wheel's mounting hub. Since the wheel is ahead
of the leading arm's forward pivot point it is said to "lead"
the arm's fixed point. |
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| Leaf
spring |
A
suspension component composed of long, flat, flexible steel pieces
that suspends a vehicle. Most leaf springs are a composed of one main
leaf spring with eyelets on each side which mount to the frame with
several smaller leaves banded to the main leaf. A solid rear axle
is bolted to the center of the leaf springs. At one time, nearly all
cars and trucks used leaf springs for front and rear suspension, but
independent suspension has replaced leaf springs in nearly all cars.
Trucks and most sport utility vehicles still use leaf springs to locate
and suspend their rear axles. A fiberglass composite rear leaf spring
was used on the Chevrolet Corvette beginning in 1991. |
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| Lean |
An
air/fuel mixture that contains more air than necessary for normal
combustion. An undesirable condition that can cause an engine to hesitate,
idle improperly, and produce lower than normal power. Opposite of
Rich. |
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| Leather
seats |
Seat
upholstered with leather. Generally leather seats are leather 'surfaced'
meaning vinyl of the same color is used on the sides and back as a
way of conserving costs. |
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| Leather
conditioner |
A
lotion usually containing lanolin or other softening agent that can
be applied to leather seats to replenish natural oils and prevent
them from becoming dry, hard and cracked. |
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| LED |
See
Light Emitting Diode |
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| Left-hand
threads |
Bolt
threads which are orientated in the opposite direction than normal.
Tightening requires torquing towards the left rather than the right.
Used in situations where a counterclockwise spinning shaft might work
a normal bolt loose. |
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| Left-hand
drive |
An
automobile in which the steering wheel is mounted on it's left side
such as that used in the U.S. Automobiles in England, Australia, Japan
and other countries where vehicles are driven on the left side of
the road have their steering wheels and pedals mounted on the left
side. |
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| Leg
pipes |
Another
term for side pipes. See Side pipes. |
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| Lemon |
A
term applied to a vehicle plagued with problems. |
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| Lemon
law |
State
laws which specifically outline what constitutes a lemon. Owners who's
vehicles have reoccurring problems that qualify under the laws can
legally seek reimbursement, exchange, or legal action from the manufacturer.
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| Leveling |
See
Automatic leveling. |
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| Lever-arm
shock absorber |
A
type of suspension and shock absorber design used on some British
cars where a lever arm attached to the wheel hub actuated a shock
absorber. |
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| Lexan |
The
name of a clear shatterproof plastic developed by DuPont which is
used as side windows on some automobiles. Also used as windshields
on some race cars. Similar to Plexiglas. |
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| Lift |
Raising
an off-road vehicle to increase it's frame-to-ground clearance and
therefore it's off-road capabilities. By increasing a truck's clearance,
it can accommodate larger tires and traverse larger obstacles such
as stumps, rocks and ruts. Aftermarket companies produce lift kits
of two main types: body lifts and suspension lifts. A body
lift generally consists of taller rubber bushings which
replace the OEM frame-to-body bushings raising the body off the
frame several inches. A more expensive suspension lift
includes replacement springs and suspension arms as well as a new,
dropped pitman arm and extended brake lines to maintain correct
steering geometry and braking safety. Many states have enacted laws
which limit the amount of lift.
Also,
the term lift is used to describe the tendency of a vehicle's rear
end to lift during braking and the tendency of the front end of
a rear-wheel-drive car to lift during acceleration.
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| Liftback
|
A
car with a fastback body style that incorporates a hatchback. See
Hatchback, Fastback. |
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| Lifter |
A
cylindrical device inside the motor that is moved by the camshaft
and acts as an intermediate device to actuate the engine's intake
and exhaust valves. Used in all pushrod-type engines and many overhead
valve engines where the rocker arms aren't directly controlled by
the camshaft. |
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| Liftgate
|
A
hinged rear door such as used on minivans and sport utility vehicles
that lifts upward. Also called Tailgate. |
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| Lift
kit |
A
preassembled kit that includes the necessary items to "lift"
or increase a truck or sport utility's ground clearance. See Lift
(above). |
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| Lift
struts/supports |
See
Hood struts. |
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| Light |
An
early automotive term that signified a car's side or door windows.
A "four-light" car had four doors (a window on each door),
a "two-light" car had two doors. The rear window was often
referred to as the Backlight, or Backlite. |
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| Light-actuated
pickup |
An
optical sensor used in some modern vehicles' ignition system instead
of a distributor. Similar concept as a magnetic pickup. Also referred
to as an Optical pickup or Optical/Light sensor. |
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| Light
alloy |
A
term for a lightweight alloy made of aluminum or magnesium. |
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| Light-emitting
diode (LED) |
A
semiconductor diode that emits light when current flows through
it. LED colors are Infrared, red, orange, yellow, green and blue.
LED's
are being used more an more on vehicles to replace standard incandescent
light bulbs because they are brighter, use less current, produce
less heat and last longer. An arrangement of many LED's are now
beginning to be used as taillights for semi-trucks and third row
brake lights for automobiles. The advantage is, the loss of one
or two burnt out bulbs won't affect visibility of the entire taillight
arrangement.
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| Limited
slip differential |
A
differential that typically uses clutch discs and springs to lock
both rear axles together so that power is applied to both wheels.
Greatly improves traction. In a conventional differential, one wheel
is the main drive wheel and power goes to the wheel with the least
traction. A limited slip differential applies traction to both wheels
regardless of traction. By using clutch discs, some differentiation
between the axle speeds can occur such as then vehicle is making a
sharp turn (the outer wheel makes more revolutions because it turns
in a larger circle). |
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| Limousine |
A
term often used to describe a stretched luxury car (usually a full-sized
Lincoln or Cadillac) that is chauffeur-driven and passengers are
separated from the driver with a glass window.
Limousines
are usually custom built by limousine manufacturers who buy vehicles
from the manufacturer. Customization begins by cutting the cars
in half, adding additional supports to the frame to accommodate
the additional weight/length (sometimes installing new frame members),
beefing up the suspension with heavier springs and even installing
suspension and brake systems from full-size pickup trucks. Finally,
new sheet metal is added to the spliced region and a custom interior
job is applied. The most common type of vehicles used for limousine
in the U.S. are full-sized Cadillacs and Lincolns.
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| Line |
In
racing, it's an imaginary path through a corner that allows late
braking and high cornering speed to achieve the fastest possible
speed around the corner.
In
off-road terms, it's an imaginary path a vehicle can take that will
allow the vehicle to traverse or maneuver around obstacles with
the least chance of getting stuck or causing vehicle damage.
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| Liner |
A
metal sleeve that fits into a cylinder bore that the piston rides
in. Cylinder liners are used widely in large commercial diesel motors
and can be removed from an engine for servicing or replacing. Dry
Liners (also called a Sleeve) are relatively thin and fit inside
a machined bore. Wet Liners are thicker because they do not fit inside
a bore. They make up the entire cylinder and are surrounded by coolant. |
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| Lining |
The
thin layer of friction material adhered to brake pads and brake shoes
that contacts moving discs or brake drums to slow a vehicle down.
Asbestos was once widely used as a friction material but has since
been replaced with other, safer, organic compounds. Semi-metallic
linings have metal particles imbedded into the friction material that
holds up better under higher brake temperatures and helps reduce brake
fade. Brake linings are typically fastened to the metal brake shoe
or pad with rivets or with cement. Brake linings were once replaceable,
however, very few (if any) shops today actually replace just the linings,
rather the whole shoe or pad is replaced. |
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| Link |
A
steering or suspension member or arm with a connecting link on each
end.
Also,
a single segment of a chain
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| Linkage |
A
system of rods and levers that transmits motion from one device to
another. A common example is the transmission shift linkage which
connects a shifter mounted to the steering column or floor to the
transmission via multiple levers and rods. |
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Liquefied
Petroleum Gas (LPG)
|
Commonly
called Propane. LPG typically consists of butane and propane mixed.
Used as a alternative fuel in many vehicles, particularly municipal
and fleet vehicles (police cars). Some advantages of LPG are reduced
engine maintenance, lower exhaust emissions and lower fuel costs.
On the down side, converting to LPG requires certain vehicle modifications
such as installing stainless steel exhaust valves, and refueling sources
are limited. LPG must also be stored in a sturdy (heavy) pressurized
tank as a liquid. |
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| Liquid
Crystal Display (LCD) |
A
type of digital display used with automotive diagnostic instruments,
GPS systems, car stereos and onboard computer monitors. Transparent
electrodes are sandwiched between two plates of glass along with a
liquid crystal material. When voltage is applied to the electrodes
the molecular orientation of the crystal liquid material is altered
which modifies the amount of light which can pass through -- making
visible. Liquid crystal displays have become cheaper and more sophisticated
and are being used more frequently inside automobiles. Compared to
traditional cathode ray tube (CRT) displays, LCD's are more compact,
cheaper to produce, weigh less, use far less current and produce almost
no heat or radiation. |
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| Liter |
A
metric unit of capacity equal to 1000 cubic centimeters. Used by most
countries to measure liquids and volume. In automobiles, engine cylinder
displacement is measured in liters (e.g.. a 350 cu. in. motor equals
5.7 liters). Similar in size to a U.S. quart. One gallon equals 3.785
liters. |
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| Live
axle |
A
solid axle assembly consisting of axles and a differential inside
a single housing. Frequently found on the rear end of most pickup
trucks, SUV's and front engine, rear-wheel-drive cars. |
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| Loaded
radius |
The
distance from the center of the wheel to the bottom of the tire and
takes into consideration reduced height due to tire bulge from vehicle
weight. In contrast, free radius is measured from the center of the
wheel to the top of the tire and does not factor in tire bulge created
by vehicle weight or cargo. Used by racers and automotive/tire engineers. |
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| Loaded
section height |
The
height of a tire measured from the road surface to the bead. Due to
tire-bulge from the vehicle's weight and cargo, the loaded section
height will be less than the tire's normal section height (distance
between treat and bead measured at top of tire). |
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| Load
index |
A
number usually printed on the sidewall of a tire that represents the
amount of weight it can carry (when properly inflated) as determined
by the tire manufacturer. |
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| Load
range |
An
alphabetical index used for classifying a tire's weight carrying capacity,
inflation limits (lb/PSI) and service requirements, as related to
it's ply rating (number of belts used in the tire's construction).
The more weight a tire must (or can) carry the more plies it typically
uses - for strength. Tires used on passenger cars have a low load
range rating usually A or B (2, 4 plies respectively). Light truck
tires are typically rated at C, D & E (6, 8, 10 plies) all the
way up to N (24 plies) used on big rigs. A tire's load range is printed
on it's sidewall. |
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| Lobe |
The
high spot on a camshaft's eccentric that lifts open a valve. By adjusting
the height and curvature of a lobe, manufacturers can determine the
height and duration that a valve opens. High performance camshafts
typically used tall lobes that open the valves more and hold them
open longer. The result is greater opportunity for intake gasses to
enter and exhaust gasses to escape the combustion chamber. |
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| Locking
gas cap |
A
fuel cap with a lock. Restricts entry to the fuel tank. |
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| Locking
hubs |
Front
wheel hubs used on four-wheel-drive vehicles which can be switched
between "locked" and "free" modes to reduce
wear on the front differential gears and driveshaft when four-wheel-drive
is not in use. Switching can be accomplished electrically with solenoid
on the axle or in the hubs themselves, or manually by turning a
dial on each front hub. In the "locked" position, the
hub and wheel are locked to the front axle and torque can be applied
to the wheel. In the "free" position the wheel can freewheel,
meaning it does not turn the axle or any gears while it is cruising
down the road -- resulting in reduced drivetrain wear and increased
economy.
Although
there has been a move towards automatic systems, off-road enthusiasts
appreciate the ruggedness and certainty of manual locking hubs.
Also
see, Four-wheel-drive, Shift-on-the-fly and Approach angle.
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| Lockout
switch |
A
switch that prevents a user from using certain functions. Most common
application is a window lockout switch which allows the driver to
disable other power window switches usually to prevent children
from opening windows.
Another
application allows the interior door latches to be disabled by moving
a toggle switch in the door jamb. The door can be opened from the
outside but not the inside. Prevents children from accidentally
opening doors while driving.
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| Lock-to-lock |
The
furthest a steering wheel can be turned -- from the furthest point
to the furthestmost point in the other direction until the steering
wheel stops (locks). Often used by engineers to judge steering ratios
by noting the number of revolutions required to turn the wheel all
the way one direction to all the way the opposite direction. |
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| Lockup |
A
term often used to describe when the brakes are applied with enough
force they stop the wheels and lead to a skid. Antilock brake systems
prevent wheel lockup allowing a driver to have steering control
while making panic stops.
Also
used to describe when a lockup torque converter "locks"
to engine rpm electromechanically. Results in greater fuel economy.
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| Lockup
torque converter |
A
type of torque converter used in modern automatic transmissions where
the converter's output shaft locks in place eliminating slippage between
the motor and the transmission. Lockup typically occurs at higher
speeds (40-50 MPH). The result is greater fuel economy and more power
at higher speeds. |
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| Longitudinal
link |
A
suspension link that is positioned parallel to the length of the vehicle. |
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Longitudinal
location/
orientation |
Where
a motor is placed in a longitudinal (parallel) plane with the vehicle
such as in most rear-wheel drive vehicles. A few front wheel drive
vehicles also use the same design scheme. |
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| Loose |
Typically
meaning loose steering/handling. Lack of steering response caused
by worn suspension components such as ball joints and bushings.
In
racing, 'Loose' refers to oversteer because the rear end of the
vehicle feels like it wants to swing wide during turns.
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| Louver |
Slots
in the hood or other body panels usually intended to increase airflow
around the engine or other components for cooling.
Also
a popular design 'trick' street rodders, used for aesthetics.
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| Low
back seat |
A
car seat with a low backrest generally without a headrest. Commonly
found on classic cars such as early Mustangs, Corvettes and Thunderbirds. |
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| Low
beam(s) |
The
low (dim) headlight setting used for most night driving. In a two-lightbulb
vehicle, it is the primary filament (two in each bulb--the other for
bright lights). In a four-light setup, low beam and high beam bulbs
are separate. Low beam headlights work better in fog because the lights
are aimed lower (fog tends to hover above the road surface), is less
intense than high beams, meaning less light is reflected off water
droplets suspended in the air and back into the driver's eyes. |
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| Low
gear |
First
gear in manual transmissions. In automatic transmissions low gear
is designated by a L or L1. |
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| Low-speed
circuit |
See
Idle circuit. |
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| Low-tension
leads |
Wires
associated with the ignition system that carry low voltage (6-12)
volts such as battery cables and wiring to the switch, coil and distributor. |
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| LPG |
See
Liquefied Petroleum Gas. |
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| Lubricant |
A
substance, usually oil or grease, used to reduce friction between
moving parts. Lubricants also help form a seal around parts such as
piston rings and valve guides. Different kinds of lubricants are used
in vehicles depending on specific needs - grease on door hinges and
power accessories, motor oil in the crankcase, gear lube (thicker)
in manual transmissions and rear differentials. Even though automatic
transmission fluid (ATF), power steering and brake fluid are used
for hydraulic purposes, they are also used to help seal and lubricate
parts. |
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| Lubrication
system |
Oil
galleries and other components of an engine's oiling system that are
involved in feeding pressurized oil throughout an engine to cool and
lubricate parts. An engine's lubricating components include: oil pan,
oil pump, oil galleries and tubing, oil filter and oil coolers. |
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| Lug
bolt |
A
bolt used to fasten a wheel to a vehicle's hub. Most vehicles, however,
don't use lug bolts, rather they use lug nuts. Lug nuts
fit over studs that are pressed into the axle or drive hub. One advantage
of using studs instead of bolts is it is easier to position the wheels
onto the hub. |
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| Lug
nut |
A
nut used to fasten a wheel to a vehicle's hub. Most vehicle's use
four or five lug nuts per wheel. Most four-wheel-drive pickup trucks
use six lugs per wheel. 3/4 ton and higher trucks usually use eight
lugs per wheel. Large trucks may use 10 lug nut or more per wheel.
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| Lug
wrench |
A
wrench usually supplied by the manufacturer which can be used to loosen
wheel lug nuts or bolts. |
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| Luggage
compartment |
Same
as Trunk. A storage area usually in the rear of a car behind the rear
wheels. |
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| Luggage
rack |
A
rack, usually made of metal or plastic, that mounts to a vehicle roof
for hauling items on the roof such as luggage. Prevents luggage or
items from shifting or sliding during transport. |
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| Lugging |
Driving
a vehicle in a gear that is too high, and engine rpm too low for a
given speed or driving condition. The result is a jerking feeling
and the sense that the motor may soon quit. |
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| Lugs |
Tread
blocks on tires. Usually associated with large tread blocks like those
found on large truck tires. Manufacturers often use different sized
lugs and stager their position to reduce tire noise. |
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| Lumbar
support |
How
well a seat supports an occupant's lower back (lumbar region). Quality
seats have good lumbar support, often adjustable, which reduces diver
fatigue, particularly during long trips. |
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