ONE-WIRE CIRCUIT- One that uses the vehicle frame as a return wire to the power source.

OPEN CIRCUIT- Electrical circuit with a gap or break in continuity so that current cannot flow.

OPEN LOOP- Control system using preset values in the computer to operate the engine.

OUTBOARD CV-JOINT- The outer universal joint on a front-wheel drive vehicle.

OUTER STUB SHAFT- In a front-wheel drive vehicle, the short shaft connecting outer universal joint and the front-wheel hub.

OUTPUT- The signal sent by a computer as a result of processing inputs it has received.

OUTPUT SHAFT- Transmission shaft on which the output gears are mounted.

OUTPUT SHAFT GEARS- Gears that turn the output shaft of a manual transmission.

OVERDRIVE RATIO- The situation in which a large gear is used to drive a smaller gear with an increase in speed as a result.

OVERRUNNING CLUTCH- Device that locks a pinion gear in one direction and releases it in the other.

PACKING WHEEL BEARINGS- Filling the bearing shells with grease to prevent excessive wear.

PARKING PAWL- A latch that locks the transmission so that the vehicle will not roll when the selector lever is in the PARK position.

PEDAL FREE PLAY- The amount of brake pedal movement before braking action begins to take place.

PEDAL HEIGHT- Distance of the brake pedal above the floor of the vehicle.

PICKUP COIL- Component that sends pulses to the control unit of an electronic ignition system as a result of trigger wheel action.

PICKUP COIL AIR GAP- The space between the pickup coil and the trigger wheel tooth.

PILOT BEARING- The bushing or bearing that supports the forward end of the transmission input shaft.

PINION GEAR- Differential gear turned by the drive line. It meshes with the ring gear. Also, a gearbox component that meshes with the rack gear or a small gear on a starter motor that engages a larger gear to rotate the engine flywheel.

PINION GEAR BEARING PRELOAD- Degree of tightness of bearings, adjusted by compressing a spacer or using shims.

PINION GEAR CLEARANCE- Distance between the pinion gear and drive end frame when the gear is engaged.

PINION GEAR DEPTH- The distance the pinion gear extends into the carrier to mesh with the ring gear.

PINION PILOT BEARING- A bearing used to support the pinion gear in the differential.

PINION SHAFT- Shaft holding the two differential idler (pinion) gears.

PITCH LINE- Imaginary line along the center of a gear tooth.

PITMAN ARM- Component that transfers gearbox motion to the steering linkage.

PITMAN SHAFT OVER-CENTER ADJUST-MENT- Adjustment of clearance between the sector gear and the ball nut teeth in a recirculating ball gearbox.

PLANETARY GEARSET- A set of gears consisting of several "planet" gears rotating around a central "sun" gear.

PLUG GAP- Distance between the center and side electrodes on a spark plug.

PLUG HEAT RANGE- Numeric indicator of how hot a spark the plug will develop.

PLUG REACH- Length of the threaded portion of a spark plug.

PLY SEPARATION- Pulling apart of tire plies as a result of overheating due to under inflation or other causes.

POLE PIECE- Magnetic component of a motor that keeps the armature rotating.

POWER STEERING FLUID- A hydraulic oil, usually automatic transmission fluid.

POWER STEERING PRESSURE TEST- Use of a pressure gauge to check pump and associated components for correct pressure.

POWER STEERING PUMP- Unit that provides the hydraulic pressure needed in a power steering system.

POWER TRAIN- Gearing system and other components used. to transfer energy from the engine to the wheels of the vehicle.

PRESSURE BLEEDING- A method of system bleeding using additional pressure supplied by an external air tank.

PRESSURE PLATE- Spring-loaded device that clamps the clutch disc against the flywheel.

PRESSURE PLATE COVER- Lid that bolts on the pressure plate to hold various components in place.

PRESSURE PLATE FACE- A large ring that contacts the friction disc as the clutch engages.

PRESSURE PLATE RELEASE LEVERS- Levers hinged inside the pressure plate that help move the pressure plate face away from the clutch disc and flywheel.

PRIMARY AND SECONDARY SHOES- Front and back shoes in a drum brake system. The secondary shoe has a larger surface area.

PRIMARY CIRCUIT- In an ignition system, all components are operating on battery (low) voltage.

PRIMARY WIRE- Small insulated conductor that carries battery or alternator voltage.

PROPORTIONING VALVE- Valve designed to equalize pressure at the wheel cylinders on vehicles with front disc and rear drum brakes.

PULLING BRAKES- Situation in which a vehicle veers to one side when the brakes are applied.

QUICK CHARGE TEST- A method of determining whether battery plates are sulfated (no longer able to hold a charge).

RACK AND PINION STEERING GEAR- A steering gear in which a pinion of the end of the steering shaft meshes with a rack of gear teeth on the major cross member of the steering linkage.

RACK AND PINION STEERING GEAR ADJUSTMENT- Tightening or loosening rack adjustment screw as needed for optimum steering.

RADIAL RUNOUT- Uneven rotation caused by differences in diameter.

RADIAL TIRE- One that has cord plies running straight across, from bead to bead. Additional stabilizer plies are placed beneath the tread.

READING SPARK PLUGS- Determining cause of a problem by examining condition of the spark plug.
READING TIRES- Identifying alignment, suspension, and other problems through the wear patterns on tire treads.

REAR AXLE ASSEMBLY- A combination of gears and axles converting rotary motion of the drive shaft to forward or backward motion of a vehicle.

REAR AXLE RATIO- The relationship between the numbers of teeth on the pinion gear and ring gear. Ratio affects acceleration, pulling power, and fuel economy.

REAR DRIVE AXLE ASSEMBLY- Differential, axles, and other components transferring power from the drive line to the rear wheels.

REAR DRIVE AXLES- The components that transmit power from the differential gears to the wheels.

RECIRCULATING BALL- Most common type of gearbox used with linkage steering system.

RECTIFIED- Term used to describe ac current that has been changed to dc.

REDUCTION STARTER- One that uses extra gears to increase the torque applied to the flywheel gear.

REGULATOR BYPASS TEST- Test that connects full battery voltage to the alternator field, leaving the regulator out of the circuit.

REGULATOR VOLTAGE TEST- Test the charging system under low output, low load conditions.

RELAY -Electrically operated switch.
RESERVE CAPACITY RATING- The amount of time a battery will continue to provide as acceptable current flow when not being recharged by the alternator.

RESERVE DISTANCE- Amount of travel remaining between pedal and floor when the brakes are applied.

RESISTANCE- Opposition to current flow.
RESISTANCE PLUG WIRE- Special type of spark plug wire that eliminates most radio interference.

RETRACTING AND HOLD-DOWN SPRINGS- Springs that pull the shoes away from the brake drum surface when the pedal is released.

REVERSE BIAS- Arrangement in which a diode acts as an insulator.

REVERSE IDLER SHAFT- Shaft in a manual transmission on which the reverse idler gear is mounted.

REVERSE POLARITY- Accidental backward connection of primary wires.

RING AND PINION BACKLASH- The amount of space between the meshing gear teeth.

RING AND PINION NOISE- Whining or howling sounds that change pitch with speed change, usually cause by wear or damage to differential components.

RING GEAR- Large gear in the differential that is driven by the pinion gear and, in turn, drives the spider gears.

RING GEAR RUNOUT- The amount of wobble that occurs as the gear rotates.

ROLLING RESISTANCE- A measure of the amount of resistance that is generated as a tire rolls on the road surface.

ROTOR- A rotating contact inside the distributor that routes electrical pulses from the coil to the spark plugs. Also, the metal disc against which brake pads are forced to stop a vehicle.

ROTOR CURRENT TEST- Method used to check alternator windings for an internal short.

ROTOR WINDING OPEN- An open (broken) winding in an alternator rotor.

ROTOR WINDING SHORT- A short-to-ground fault in an alternator rotor.

RZEPPA CV-JOINT- Ball-and-cage type constant velocity joint used on front-wheel drive vehicles.