ASE T-Series flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Wet compression test

A compression test repeated after adding a small amount of oil to the cylinder; a pressure increase indicates worn piston rings, while no change points to valve or head gasket leakage.

Cylinder leakage test

Shop air is applied to a cylinder at top dead center on compression; escaping air is located by sound at the oil filler (rings), throttle body (intake valve), tailpipe (exhaust valve), or radiator bubbles (head gasket).

Stoichiometric air-fuel ratio

The chemically ideal mixture for gasoline, about 14.7 pounds of air to 1 pound of fuel, at which combustion consumes essentially all of the oxygen and the fuel.

PCV system function

The positive crankcase ventilation valve meters crankcase vapors back into the intake so they are burned; a clogged valve causes crankcase pressure, oil leaks, and rough idle.

Cetane number

A rating of diesel fuel ignition quality; higher cetane fuel ignites sooner after injection, shortening ignition delay and improving cold starts and idle smoothness.

Diesel compression-release brake

Also called a Jake brake; it opens the exhaust valve near top dead center of the compression stroke, releasing compressed air so the engine absorbs energy and slows the vehicle.

Diesel exhaust smoke colors

Black smoke indicates overfueling or an air restriction, white smoke indicates a cold engine or retarded timing with unburned fuel, and blue smoke indicates burning lubricating oil.

Wet-sleeve liner cavitation

Cylinder liner pitting caused by coolant vapor bubbles collapsing against the liner; it is prevented by maintaining the correct coolant nitrite (SCA) concentration and pH.

Axle ratio calculation

Divide the ring gear tooth count by the pinion tooth count; a 41-tooth ring gear and an 11-tooth pinion produce a 3.73:1 axle ratio.

Driveline U-joint phasing

The yokes at both ends of a driveshaft must be aligned in the same plane so the two U-joints cancel each other's speed variation; misphasing causes vibration.

Limited-slip friction modifier

An additive required in limited-slip differentials to prevent clutch plate chatter during turns; missing or depleted modifier causes noise and grabbing in tight turns.

Automatic transmission stall test

With the brakes held and throttle wide open in a drive range, engine speed is compared to specification to evaluate torque converter and clutch pack condition.

Governor cut-out pressure

The air pressure at which the compressor governor stops the compressor from building more pressure, typically about 120 to 135 psi on a heavy truck system.

Slack adjuster pushrod stroke

The distance the brake chamber pushrod travels; when it exceeds the adjustment limit stamped on the chamber, the brake is out of adjustment and must be corrected.

Low air pressure warning

A buzzer or light that must activate before system pressure falls below 60 psi, warning the driver before the spring brakes apply automatically.

DOT 5 brake fluid

A silicone-based brake fluid that is not compatible with DOT 3 or DOT 4 glycol fluids; mixing them can cause seal swelling and brake failure.

Positive caster effect

Caster tilts the steering axis so its top leans rearward; more positive caster increases straight-line stability and steering return but also increases steering effort.

Thrust angle

The angle of the rear axle centerline relative to the vehicle's geometric centerline; a nonzero thrust angle causes dog tracking and an off-center steering wheel.

Included angle

The sum of camber and steering axis inclination; comparing it side to side reveals a bent spindle, strut, or knuckle even when camber has been adjusted to specification.

Feathered tire wear

Tread worn in a sawtooth pattern across the rib edges, caused by incorrect toe; the sharp edges point in the direction the tire is scraping.

Voltage drop test

Measuring the voltage lost across a circuit while it operates under load; total drop should be under about 0.5 volt, and each connection under 0.1 volt.

Battery state of charge

Estimated from open-circuit voltage after surface charge is removed: about 12.6 volts is 100 percent, 12.4 volts is 75 percent, and 12.2 volts is 50 percent.

Parasitic draw

Current drawn from the battery when all modules are asleep and everything is off; more than roughly 50 milliamps indicates a fault that will drain the battery.

J1939 data bus termination

Two 120-ohm resistors at the ends of the bus are in parallel, so a good bus measures about 60 ohms between CAN high and CAN low.

Superheat

The number of degrees the refrigerant at the evaporator outlet is above its saturation temperature for the measured low-side pressure; it confirms the refrigerant is fully vaporized.

A/C undercharge symptoms

Both low-side and high-side pressures read below normal, cooling is poor, and the compressor may cycle rapidly because the refrigerant charge is low.

Receiver-drier function

Stores liquid refrigerant and removes moisture and debris from the system; a restricted drier causes a temperature drop or frost across its fittings.

Evacuation to 500 microns

Pulling a deep vacuum removes air and moisture before charging; the system should hold that vacuum for several minutes to prove it is leak free.

Steer tire tread minimum

FMCSA requires at least 4/32 inch of tread depth on front steer tires and 2/32 inch on all other tires of a commercial vehicle.

Driver Vehicle Inspection Report

A report in which the driver records defects found during a required pre-trip or post-trip inspection so the carrier can certify that repairs were made.

Cold tire inflation check

Tire pressure is set to the placard value when tires are at ambient temperature; hot tires must never be bled down because pressure rises normally with heat.

Oil analysis purpose

Laboratory testing of used oil for wear metals, fuel dilution, coolant, and silicon; trends reveal internal wear or contamination before a failure occurs.