Cert III Heavy Commercial Vehicle cheat sheet

Work health and safety duty of care applies to every task: identify hazards, assess risk, and apply the hierarchy of controls before starting any repair.

A diesel engine's compression ratio typically ranges from 14:1 to 23:1; higher ratios improve thermal efficiency but raise peak cylinder pressure and NOx formation.

Four-stroke cycle order is intake, compression, power, exhaust; a six-cylinder inline engine fires every 120 degrees of crankshaft rotation.

Torque is force times perpendicular distance (T = F x d); a 300 N force on a 0.5 m wrench applies 150 Nm.

Hydraulic pressure equals force divided by piston area (P = F/A); doubling bore area halves pressure for the same load.

Electrical power in a DC circuit is volts times amps (P = V x I); a 24 V circuit drawing 40 A consumes 960 W.

A vehicle's gross vehicle mass (GVM) is the maximum loaded mass specified by the manufacturer, while gross combination mass (GCM) covers the towing vehicle plus trailer.

Brake system inspection requires minimum friction material thickness and drum/disc wear limits measured against the manufacturer's specification, not an assumed figure.

Battery safety: disconnect the negative (earth) terminal first and reconnect it last to avoid short circuits through the chassis.

A constant-mesh manual gearbox keeps gears permanently in mesh; sliding synchroniser sleeves lock the selected gear to the output shaft.

Gear ratio equals driven gear teeth divided by driving gear teeth; a 12-tooth driving gear and 48-tooth driven gear give a 4:1 reduction.

Output shaft speed equals input shaft speed divided by the gear ratio; 1800 rpm input at 4:1 yields 450 rpm output.

A synchromesh cone clutch equalises shaft speeds before dog-tooth engagement; worn baulk rings cause gear clash on downshift.

Twin-countershaft (range-change) gearboxes split torque across two layshafts, reducing tooth loading and allowing higher torque capacity.

A range-change section doubles the available ratios; a splitter section divides each main ratio, commonly giving a 0.8 or similar step.

Clutch free play is measured at the pedal or release bearing; insufficient play causes release bearing drag and clutch slip.

Air-assisted clutch actuation uses a servo booster; loss of air pressure typically results in a clutch that cannot be disengaged.

A torque converter multiplies torque at stall through stator reaction; multiplication falls to approximately 1:1 at coupling point.

Converter stall speed is the engine speed reached at full throttle with the output shaft held stationary; it is a key diagnostic reference.

Planetary gear sets achieve ratios by holding one member (sun, ring, or carrier) and driving another; the number of teeth determines each ratio.

Automatic transmission fluid (ATF) level is checked with the transmission at operating temperature in the specified range, engine running, in the specified selector position.

A slipping torque converter clutch or worn clutch packs typically show as flare during shifts, shudder, or burnt fluid smell.

Electronic control units use input signals from throttle position, output speed, and turbine speed sensors to schedule shift points.

Retarder or transmission retarder operation reduces service brake wear; it must be disengaged on low-friction surfaces to avoid wheel lock.

Transmission fluid contamination by coolant produces a milky emulsion and requires flushing plus cooler repair, not just a fluid change.

Personal protective equipment is the last line of defence in the hierarchy of controls; it supplements but does not replace engineering controls.

Manual handling risk is reduced by mechanical aids, team lifting, and keeping loads close to the body's centre of gravity.

Isolation before maintenance follows lock-out/tag-out: identify all energy sources, isolate, lock, tag, and verify by test.

A fire extinguisher is selected by class: Class A for ordinary combustibles, Class B for flammable liquids, Class C for flammable gases, and Class E for electrical equipment.

Environmental duty requires containment of spills with absorbent material and correct disposal of waste oil through licensed recyclers.

Vehicle lifting points are specified by the manufacturer; jack stands must be rated above the supported mass and placed on stable ground.

A job card or work order records the complaint, cause, and correction; accurate documentation supports warranty and audit requirements.

Measuring tools require calibration checks; a torque wrench should be verified against a known standard at intervals specified by the workshop.

A systematic diagnostic process is verify the complaint, gather information, test, isolate the fault, repair, then confirm the repair.

Voltage drop testing measures resistance in a live circuit; more than 0.5 V drop on a heavy vehicle earth circuit indicates excessive resistance.

Multimeter continuity testing is performed with the circuit de-energised; measuring resistance on a live circuit can damage the meter.

Diagnostic trouble codes identify a circuit or system, not necessarily the failed component; the code is a starting point for testing.

A compression test on a diesel engine compares cylinders within a specified percentage; a low cylinder indicates ring, valve, or head gasket leakage.

Bearing failure analysis distinguishes fatigue spalling, contamination, and inadequate lubrication by the wear pattern and colour.

Fastener torque values apply to clean, lubricated, or dry threads as specified; changing thread condition alters the achieved clamp load.

A road test after repair confirms operation under load and validates that no new faults were introduced.

Australian Design Rules set vehicle standards for braking, emissions, lighting, and noise that apply to heavy vehicles supplied to the market.

The National Heavy Vehicle Regulator administers heavy vehicle access, mass, and dimension requirements across jurisdictions.

A defect notice requires the vehicle to be repaired and inspected before it may be used again; operating contrary to a notice is an offence.

Maintenance records must show the date, odometer reading, work performed, and parts used to demonstrate compliance.

Hazard reporting should be documented and escalated to a supervisor; unresolved hazards are recorded and monitored until controlled.

Safe work method statements are required for high-risk construction work and must be reviewed when the task or conditions change.

Communication with a customer about a fault includes describing the symptom in plain language and confirming authorisation before additional work.

Waste classification separates used oil, solvents, batteries, and tyres; each stream has its own storage and disposal requirements.

A torque wrench is stored at its lowest setting to prevent spring fatigue and loss of calibration.

Hydraulic presses and pullers apply controlled force; never use heat on components containing sealed bearings or pressurised fluids.

Micrometers are read by combining the barrel scale with the thimble scale; a 0.01 mm resolution requires careful parallax-free reading.

Vernier calipers are checked for zero error before use; a positive zero error is subtracted from the measured reading.

Torque-to-yield fasteners are tightened to a torque then rotated a specified angle; they are single-use and must not be reused.

Air tools require lubrication and correct pressure; excessive pressure accelerates wear and can damage fasteners.

Battery charging releases hydrogen; ventilation and removal of ignition sources are required in the charging area.

Lifting slings and chains are inspected before use for cuts, distortion, and tag validity; damaged slings are removed from service.