Craftsman Motor Vehicles Maintenance cheat sheet

Lifting rule: jack only under manufacturer-designated lift points; always place axle stands before any part of the body goes under the raised vehicle - a hydraulic jack is a lifting device, not a support.

Torque wrench selection rule: the target value should fall between 20% and 100% of the wrench's rated range; a 20-100 N·m wrench should not be used for a 15 N·m fastener.

Torque conversion: 1 kgf·m = 9.81 N·m; 1 lbf·ft = 1.356 N·m; 1 lbf·in = 0.113 N·m. Tightening torque is measured on the fastener thread, so lubricated threads need lower torque than dry threads.

Torque-to-yield (TTY) bolts stretch plastically during tightening and must be replaced, not reused; they are usually tightened to a torque plus a specified angle (e.g. 40 N·m + 90°).

Fire classes: A = solids (water/foam), B = flammable liquids (foam, CO2, dry powder - never water), C = gases, D = metals, E = live electrical (CO2 or dry powder only).

Battery charging area rule: lead-acid charging releases hydrogen; no open flame or sparks, ventilate the area, and disconnect the negative terminal first and reconnect it last.

Hand tool safety rule: never use a cheater bar on a ratchet or torque wrench; use a breaker bar for loosening and the torque wrench for final tightening only.

Personal protective equipment baseline in the workshop: safety glasses when grinding, drilling, or working under a vehicle; gloves for chemicals and sharp edges; steel-toe boots for any load handling; ear protection above 85 dB(A).

Measurement tool accuracy: a vernier caliper typically resolves 0.02 mm, a micrometer 0.01 mm, and a dial bore gauge 0.01 mm; check zero before each measuring session and store micrometers with the anvil open.

Oil pressure warning at idle with correct oil level points to worn bearings, a stuck relief valve, or a failing oil pump - verify with a mechanical gauge before condemning the pump.

Engine oil viscosity notation (e.g. 5W-30): the first number is the cold (W = winter) pumping behaviour, the second is kinematic viscosity at 100 °C; both must match the manufacturer specification, including API/ACEA grade.

Coolant boiling point rises with system pressure: a 15 psi (approx. 1 bar) cap raises the boiling point of a 50/50 glycol mix by roughly 25 °C, so a weak cap causes overheating under load.

Thermostat diagnosis: an engine that never reaches operating temperature or cools at speed has a thermostat stuck open; rapid overheating at low speed with a cold radiator hose suggests stuck closed.

Cooling system pressure test: pump to the cap rating, hold and observe; a falling gauge with no external leak indicates an internal leak (head gasket, heater core, or EGR cooler).

Air-fuel ratio basics: stoichiometric petrol is about 14.7:1 by mass; rich mixtures (lambda < 1) cool combustion and raise HC/CO, lean mixtures (lambda > 1) raise NOx and risk detonation.

Fuel trim interpretation: long-term fuel trim above about +10% indicates a lean condition (vacuum leak, weak pump, dirty injector); below about -10% indicates rich (leaking injector, high fuel pressure, faulty sensor).

Diesel common-rail injection pressures reach 1,800-2,500 bar; never crack a high-pressure line to bleed it - the jet can penetrate skin, which is a surgical emergency.

Oil change interval logic: severe-service schedules (short trips, dust, towing) shorten intervals; used-oil analysis (iron, copper, silicon, fuel dilution) is the evidence-based way to extend them.

Compression test rule: throttle wide open, all plugs removed, engine at operating temperature; a cylinder more than 10% below the highest cylinder, or a wet/dry difference above 10%, indicates ring or bore wear.

Cylinder leakage test: pressurise each cylinder at TDC on compression with 5-7 bar; air out of the intake = intake valve, exhaust = exhaust valve, crankcase breather = rings, radiator = head gasket or cracked head.

Valve clearance check is done with the engine cold unless the manufacturer states otherwise; record every clearance and compare against the specification table before adjusting with shims or rocker screws.

Cylinder head flatness limit is typically 0.05 mm across the length and 0.02 mm across the width; measure with a straight edge and feeler gauge in both diagonals.

Timing belt replacement is interval-based, not condition-based: a belt that looks good can fail past its interval; on interference engines the result is bent valves, so replace the tensioner and water pump at the same time.

Bore measurement: measure at three heights and two planes (thrust and axial) with a bore gauge; out-of-round and taper limits are usually 0.02-0.05 mm depending on the engine.

Head gasket failure indicators: coolant loss without external leak, white exhaust smoke, bubbling in the expansion tank, mayonnaise-like emulsion in the oil, and hydrocarbon detection in the coolant.

Engine noise mapping: a deep knock at half engine speed suggests a main or big-end bearing; a lighter double knock at half speed suggests piston slap; a ticking at camshaft speed suggests valve clearance or a hydraulic lifter.

Warped or cracked heads are checked by pressure testing and crack detection (dye penetrant or magnetic particle for cast iron) before any resurfacing.

Clutch slip test: in a high gear at low speed, apply full throttle; if engine speed rises without a matching road-speed increase, the clutch is slipping - check free play and release bearing first.

Clutch drag symptoms: difficulty engaging first and reverse with the pedal fully down, and a vehicle that creeps with the pedal depressed, point to insufficient release travel or a warped friction disc.

Manual gearbox oil level is checked at the fill plug on a level vehicle; the correct level is the bottom edge of the fill hole, and the plug should be removed before draining so the box can be refilled.

CV joint diagnosis: a rhythmic clicking on full lock under power indicates a worn outer joint; vibration under acceleration with a worn inner joint; a split boot with grease loss is an immediate replacement item.

Driveshaft universal joint wear shows as a clunk on take-up and drive-line vibration; check for play in both planes and for a missing or seized needle bearing.

Automatic transmission fluid level must be checked at the manufacturer-specified temperature (often 35-45 °C) with the engine running and the selector cycled through all positions; overfilling causes foaming and aeration.

Differential gear whine that changes with speed but not with load direction suggests pinion bearing preload; whine on drive only versus coast only points to different gear contact faces.

Two-wheel-drive versus four-wheel-drive tyre rule: all four tyres on a permanent 4WD or AWD vehicle must be within a small rolling-circumference tolerance, or the centre differential winds up and fails.

Hydraulic principle: pressure is force divided by area (p = F/A); a larger master cylinder piston reduces pedal travel but increases pedal effort for the same calliper force.

Brake fluid is hygroscopic; DOT 4 has a wet boiling point of about 155 °C versus 230 °C dry, so fluid older than two years or with more than 3% water content should be replaced.

Never mix DOT 5 (silicone) with DOT 3, 4, or 5.1 (glycol); the mixture is not miscible and will damage seals and performance.

Pedal feel diagnosis: a spongy pedal indicates air in the system; a pedal that sinks slowly under constant pressure indicates an internal master cylinder leak; a hard pedal indicates a failed booster or seized calliper.

Brake pad minimum thickness is typically 2-3 mm above the backing plate; discs have a minimum thickness stamped on the hub, and below that value the disc must be replaced, not machined.

Run-out limit for a brake disc is usually 0.05 mm or less; excessive lateral run-out causes pedal pulsation and is measured with a dial gauge on the disc face.

Bleeding sequence follows the longest hydraulic path first: typically right rear, left rear, right front, left front; ABS units may require a diagnostic scan tool to cycle the pump.

Parking brake adjustment: with the lever at the specified number of clicks, the rear wheels should turn freely and lock when the lever is fully applied; cables stretch and must be adjusted at the equaliser.

Proportioning and ABS: a fault lamp on with a stored wheel-speed sensor code disables ABS and often EBD; verify sensor signal with live data before replacing parts.

Alignment angles: camber is the wheel's vertical tilt (negative = top inward); caster is the steering axis tilt (positive = top rearward) and provides straight-line stability; toe is the difference in distance between the front and rear of the wheels.

Total toe is the sum of both wheels; a positive total toe-in reduces straight-line wander but increases tyre scrub; toe is set last because it depends on camber and caster.

Thrust angle is the difference between the geometric centreline and the rear axle centreline; a non-zero thrust angle causes the steering wheel to sit off-centre and the vehicle to dog-track.

Tyre wear patterns: wear on both shoulders = under-inflation; wear in the centre = over-inflation; one-sided wear = camber or toe error; feathered tread = excessive toe.

Wheel bearing diagnosis: a growl that changes when loading the bearing left or right in a curve, or a hum that disappears when the wheel is unloaded, indicates a worn bearing; confirm with a dial gauge hub run-out check.

Ball joint play is checked with the suspension loaded and unloaded; 0.5 mm of radial play or any axial play beyond specification requires replacement, and a torn boot means replacement regardless of play.

Shock absorber test: more than two rebounds after a firm push on the corner, or visible oil misting on the body, indicates a worn damper; dampers are replaced in axle pairs.

Power steering diagnosis: whine that increases on full lock with a correct fluid level suggests pump wear or air in the system; heavy steering at idle with normal pressure at speed suggests a faulty flow-control valve.

Ohm's law: V = I × R; power P = V × I = I²R = V²/R. A 55 W headlamp on 12 V draws about 4.6 A and has a hot resistance of roughly 2.6 Ω.

Voltage drop testing is the definitive circuit test: measure across the load or cable under load; more than 0.5 V on a main power or ground circuit indicates excessive resistance.

Battery state of charge: about 12.6 V at rest is fully charged, 12.4 V is 75%, 12.2 V is 50%, and below 12.0 V is discharged; a reading below 9.6 V during a loaded cranking test indicates a failed battery.

Alternator charging voltage is typically 13.8-14.4 V at idle with loads off; below 13.2 V or above 15.0 V indicates a regulator or alternator fault.

Parasitic drain test: with all modules asleep (allow 20-60 minutes), a clamp meter should read typically below 50 mA; higher values require fuse-by-fuse isolation.

CAN bus basics: two twisted wires, CAN-High and CAN-Low, with nominal 60 Ω resistance between them (two 120 Ω terminators in parallel); 120 Ω indicates an open terminator, 0 Ω a short.

Sensor types: a two-wire inductive crank sensor generates its own AC signal; a three-wire Hall sensor needs a supply, ground, and produces a square wave - a multimeter may not capture it, so use an oscilloscope.

Relay test: 85 and 86 are the coil, 30 is the supply, 87 is the switched output, and 87a is the normally closed contact; a click without output means burnt contacts, not a faulty coil.

Tyre pressure is checked cold; pressure rises about 0.1 bar per 10 °C of temperature increase, so a hot reading must not be corrected downward.

Tread depth legal minimum is 1.6 mm across the central three-quarters of the tread; replace at 3 mm for wet performance, and check for uneven wear, cuts, bulges, and DOT date codes.

Service interval logic: fixed intervals apply to normal use; severe service (short trips, dust, towing, extended idling) halves oil and filter intervals and shortens brake and air filter checks.

Pre-trip inspection order: fluids and leaks, tyres and pressures, lights and horn, wipers and washers, brakes and steering, belts and hoses, then a road test.

Belt condition rule: glazing, cracking, fraying, or more than about 10 mm of deflection on the longest span indicates replacement; automatic tensioners should be checked for correct pointer alignment.

Brake fluid and coolant are time-based items as well as condition-based: brake fluid every 2 years, coolant per manufacturer (often 5 years or 100,000 km for long-life OAT).

Battery maintenance: clean terminals, check hold-down, and verify charging voltage; a battery that fails a conductance test should be replaced regardless of age.

Documentation rule: record mileage, date, parts used, and measured values (tread depth, pad thickness, fluid condition) so that the next service can be compared against a baseline.

Diagnostic sequence: verify the complaint, gather conditions (when, how often, hot or cold, speed, load), check for technical service bulletins, then test - never replace parts on a guess.

Intermittent faults are best captured with a data logger or flight recorder triggered by the symptom; a snapshot of live data at the moment of failure is stronger evidence than a stored code alone.

A diagnostic trouble code identifies the circuit or system, not the component: a P0301 misfire code means cylinder 1 misfired, and the cause may be spark, fuel, compression, or wiring.

Freeze-frame data records the conditions at the moment the code set (rpm, load, coolant temperature, speed); use it to reproduce the fault rather than to guess.

Customer interview checklist: what changed and when, any recent repair or fuel stop, warning lamps, noises or smells, and whether the fault is temperature or weather dependent.

Explaining a repair: state the symptom, the measured evidence, the cause, the remedy, and the consequence of deferring - avoid unexplained technical jargon and never quote a price before diagnosis.

Warranty and comeback handling: document the original complaint and repair, retain removed parts on request, and treat a repeat visit as a diagnostic failure to be re-tested, not re-argued.

Road test rule: reproduce the customer's conditions (cold start, load, speed, gradient) and record data; a fault that cannot be reproduced should be documented with the conditions tested.