Red Seal Truck and Transport Mechanic cheat sheet
Red Seal Truck and Transport Mechanic · Keep the key ideas within reach.
Occupational Skills
Before service, isolate and lock out all energy sources; verify zero energy at the control point.
Use jack stands under the frame or axle after lifting; never work under a vehicle supported only by a jack.
Torque conversion: N·m = ft·lb × 1.3558; ft·lb = N·m × 0.7376.
Read and follow the Safety Data Sheet for any chemical before handling, storage, or spill response.
A repair order must record complaint, cause, correction, parts used, and technician identification.
Measure with a calibrated micrometer or caliper; check zero and use the same units as the specification.
Disconnect the battery negative cable first and reconnect it last unless the manufacturer states otherwise.
Fastener grade markings and torque-to-yield bolts must match the manufacturer's replacement and torque procedure.
Engine and Engine Support Systems
A four-stroke diesel cycle uses intake, compression, power, and exhaust strokes; the crank turns two revolutions per cycle and the cam turns one.
Diesel ignition occurs from compressed-air heat; typical compression ratios are about 16:1 to 18:1.
A turbocharger wastegate bypasses exhaust around the turbine to limit boost; a VGT changes turbine geometry to control boost.
A charge-air cooler lowers intake air temperature after the turbocharger, increasing air density and reducing NOx.
Cooling system pressure cap: each 1 psi raises coolant boiling point about 3°F (1.7°C).
A cylinder leak-down test listens at the intake, exhaust, crankcase, and radiator to locate compression leakage.
Cylinder head bolts are usually torqued in a spiral sequence from the center outward in stages.
Excessive crankcase blowby suggests worn rings, worn cylinder walls, or failed turbo seals.
Electrical and Electronic Systems
Ohm's law: V = I × R; power: P = V × I.
Series: same current, voltage drops add, resistance adds. Parallel: same voltage, branch currents add, total resistance falls.
A fully charged 12-volt battery rests near 12.6 V; charging system output is typically about 13.8–14.8 V.
Cranking voltage below about 9.6 V at 20°C indicates a weak battery, excessive resistance, or starter draw.
Voltage-drop testing must be done with the circuit loaded; compare results with the manufacturer's limit.
A CAN bus with power off typically measures about 60 ohms between CAN high and CAN low because two 120-ohm terminators are in parallel.
Use a clamp ammeter or correct meter range for parasitic draw; do not interrupt the circuit with an unfused jumper.
Relay coils are low-current control circuits; relay contacts switch the high-current load.
Air Brake Systems
Typical compressor governor cut-out is 120–135 psi; cut-in is usually 20–25 psi below cut-out.
A low-pressure warning must activate before system pressure falls to 60 psi.
Spring brakes apply when air pressure is lost; air pressure releases them by compressing the spring.
Measure pushrod stroke and compare it with the chamber manufacturer's limit; excessive stroke requires adjustment or repair.
The air dryer removes moisture and oil; its purge valve must open during compressor unload.
A relay valve uses a control signal to speed brake application and release at remote chambers.
A tractor protection valve protects the tractor air system if the trailer breaks away or a hose separates.
After any air-brake repair, perform leak, low-pressure warning, and spring-brake tests before releasing the vehicle.
Hydraulic Brake Systems
Hydraulic pressure is transmitted equally in a confined fluid; force = pressure × piston area.
DOT 3 and DOT 4 glycol fluids absorb moisture; DOT 5 silicone fluid is not interchangeable with glycol fluid.
Bleed hydraulic brakes from the wheel farthest from the master cylinder, then follow the ABS scan-tool procedure if required.
A spongy pedal indicates air in the system or a leaking component; a fading pedal can indicate fluid boil or a leak.
Check brake hose condition for cracking, bulging, or rubbing; replace hoses that show damage.
A proportioning valve reduces rear hydraulic pressure to prevent rear-wheel lockup under light loads.
Disc brake rotor runout and thickness must be measured against specification before resurfacing or replacement.
A residual pressure valve may be used on drum-brake systems to maintain a small pressure; do not install one where not specified.
Steering and Suspension Systems
Camber is the inward or outward tilt of the wheel; negative camber tilts the top inward.
Caster is the forward or rearward tilt of the steering axis; positive caster improves straight-line stability.
Toe-in means the front of the tires are closer together; total toe is the sum of both wheel toe angles.
Set air suspension ride height and tire pressure before measuring alignment angles.
Excessive wheel-bearing play can cause steering wander, uneven tire wear, and ABS sensor damage.
Leaf springs locate the axle and carry load; a broken leaf or loose U-bolt changes pinion angle and alignment.
Shock absorbers control spring oscillation; worn shocks cause tire cupping and poor handling.
Kingpin inclination and included angle help diagnose bent steering components after impact.
Drive Train Systems
Differential ratio = ring gear teeth ÷ pinion gear teeth; higher numerical ratio means more torque and lower speed.
Driveshaft U-joint yokes must be phased per the manufacturer to cancel vibration.
Clutch free play must allow the release bearing to clear the pressure plate when the pedal is released.
Synchronizers match gear speeds before engagement; grinding during shifts indicates worn synchronizer or clutch release problems.
Limited-slip differentials may require friction modifier; use the specified lubricant.
Automatic transmission fluid level is usually checked hot, level, engine running, and in the specified range; follow OEM procedure.
A torque converter multiplies engine torque at low vehicle speed and acts as a fluid coupling at cruise.
Check rear-axle backlash and pinion preload with a dial indicator and inch-pound torque gauge per specification.
Heating, Ventilation and Air Conditioning Systems
Refrigerant cycle: compressor → condenser → expansion device → evaporator → compressor.
The condenser rejects heat and changes high-pressure vapor to liquid; the evaporator absorbs cab heat and boils liquid to vapor.
Superheat is measured at the evaporator outlet; subcooling is measured at the condenser outlet.
Moisture in an A/C system forms acids and ice; evacuate with a vacuum pump before charging.
R-134a and R-1234yf must not be mixed; use the correct refrigerant identifier and service equipment.
A receiver-drier is used with an expansion valve; an accumulator is used with an orifice tube system.
The heater core uses engine coolant; no heat can be caused by a plugged core, air lock, or blend-door fault.
Refrigerant contact can freeze skin; wear goggles and gloves and work in a ventilated area away from open flame.
Cab, Frame and Body Systems
Do not weld, heat, or drill high-strength frame rails unless the OEM repair procedure permits it.
Loose or collapsed cab mounts cause noise, vibration, and misalignment; replace per OEM.
Check door and hood alignment at hinges and latches before adjusting; worn hinges can mimic body damage.
Urethane-set glass requires the specified adhesive and cure time before vehicle use.
Before SRS work, disconnect the battery and wait the OEM-specified time for backup power to discharge.
Fifth-wheel jaw adjustment and mounting bolts must be checked for wear and torque.
Corrosion protection must be restored after panel repair to prevent rust recurrence.
Cab air suspension ride height and leveling valve adjustment affect cab height and vibration.
Fuel, Exhaust and Emission Control Systems
Cetane number rates diesel ignition quality; octane number rates gasoline resistance to knock.
Common-rail fuel systems store fuel at very high pressure; never crack a high-pressure line to bleed it.
EGR lowers combustion temperature and reduces NOx; a stuck EGR valve can cause rough idle or black smoke.
A DPF traps soot and regenerates by burning it at high exhaust temperature; excessive idling can prevent regeneration.
SCR uses DEF to reduce NOx; DEF is about 32.5% urea in water and freezes near -11°C.
A water separator/fuel filter must be drained; water in diesel can damage the high-pressure pump and injectors.
Exhaust leaks upstream of sensors can cause false oxygen or NOx readings and derate.
OBD monitors must complete before emission inspection; clearing codes resets readiness monitors.