Mechanic Motor Vehicle – 2-Year Comprehensive Notes

CLUTCHES

• Fundamental purpose – smoothly connect / disconnect engine torque to gearbox; allow gear shifting & idling.
• Working principle – Friction $T=\mu N r<em>{mean}$ where $\mu$ = friction coefficient, $N$ = axial spring force, $r</em>{mean}$ = mean radius.
• Principle employed – Friction (Q-3→C).
• Constructional variants (Q-4/5/6)
‑ Single-plate (coil or diaphragm spring)
‑ Cone
‑ Dog (positive, no slip)
‑ Multi-plate (dry / wet)
‑ Fluid coupling / torque converter (hydrodynamic).
• Noise-free option – Diaphragm spring clutch (Q-46).
• Large frictional area/simple build – Cone clutch (Q-48).
• Advantages – dog clutch: zero slip, instantaneous engagement (Q-47).
• Hydraulic single-plate clutch: pedal effort minimised (Q-49).
• Key parts & IDs
‑ Damper spring (torsion) on driven plate (Q-50)
‑ Flywheel, pressure-plate, hub etc. (Q-51).
• Inspection / tools
‑ Pressure-plate warp – straight-edge + feeler gauge (Q-11/43).
‑ Alignment – clutch-aligner mandrel (Q-12).
‑ Flywheel run-out – dial indicator (Q-13/17).
• Dual-mass flywheel – cuts gearbox/body noise (Q-44) by isolating mass via vibration damper (Q-45).

TRANSMISSION / GEARBOX

• Battery system heavy vehicles – $24\;\text V$ (Q-2).
• Gearbox types
‑ Sliding-mesh, Constant-mesh, Synchromesh (single & double cone, baulk-ring, Porsche), Automatic.
‑ Pictures Q-15/16/23/24.
• Synchromesh speciality – enables silent, easy shift while moving; eliminates sliding of gears on shafts (Q-82/83).
• Heavy commercial synchromesh – Multi & double-cone (Q-70).
• Torque multiplication (>3×) – Multi & double-cone unit (Q-69).
• Gear slip causes – excessive end-float, worn clutch, wrong lever selection (Q-76).
• Hard shift cure – adjust clutch free play (Q-78).
• Noisy neutral – worn/dry bearings (Q-79).
• Tripod C-V joint limits: axial disp. $55\,\text{mm}$ (Q-18); angle $26^{\circ}$ (Q-19).
• Pot joint angle $22^{\circ}$ (Q-34); Double joint $50^{\circ}$ (Q-32).
• Rack-and-pinion converts rotary ↔ linear motion (Q-35).
• Spur gear – straight teeth parallel axis (Q-38); Helical – multiple teeth in mesh, axial thrust; Herring-bone neutralises thrust (Q-71).
• Advantages Constant-mesh – smooth power flow (Q-41), uses helical gears (Q-42).
• Allowed pedal free-play heavy vehicle clutch $6\text–10\,\text{mm}$ (Q-66).

DRIVE-LINES & JOINTS

• Drive-line layouts – Rear-wheel (Q-21), Front-wheel (Q-22), Four-wheel, Hotchkiss vs Torque-tube (Q-29/30).
• Universal joints: cross-type, ball-&-trunnion, pot, tripod, double.
• Slip joint offers small angle + axial movement (Q-31).
• Prop-shaft connects gearbox to final-drive (Q-73); flexible torque transfer via universal (Q-74).

STEERING & SUSPENSION

• Steering purpose – guide vehicle (Q-64).
• Power steering benefit – low driver effort (Q-63).
• Types: Integral (rotary-valve), Linkage, Electronic EPS. EPS continues even if engine off (Q-135).
• Major EPS parts – motor (Q-85), rotary flow-control / unloading / relief valves (Q-86-88).
• Average p.s. ratio – $\approx 40\%$ lower than manual; general range $11{:}1\text{–}24{:}1$ (Q-99/100).
• Wheel-alignment angles
‑ Camber, Caster, King-pin-inclination, Thrust, Included, Combined.
‑ Typical combined $9^{\circ}–10^{\circ}$ (Q-96).
‑ Excess negative camber → inside-edge wear (Q-173); excess positive → outer-edge wear (Q-174).
• Suspension systems
‑ Conventional leaf (semi/quarter/full elliptical, transverse), coil spring, torsion-bar, strut (MacPherson), air, rigid vs independent.
‑ Air-bag pressure 120–125 psi (Q-113); advantage – levelling (Q-159).
‑ Weak suspension → directional instability (Q-154).
‑ Non-reactive multi-axle setup gives good rear braking (Q-149).
• Shock absorbers – telescopic (gas-pressurised, hydraulic), vane, piston, mechanical. Gas-pressure type shown Q-109/110. Automatic load-adjust unit maintains ride height (Q-153).
• Tyres & wheels
‑ Aspect ratio = % of tyre height to width (Q-119). Height = outer-dia – rim-dia (Q-120).
‑ Ply rating 14PR denotes load index (Q-123).
‑ Over-inflation – centre wear (Q-167); Under-inflation – edge wear (Q-187).
‑ Bead/plies give strength & seat (Q-168).
‑ TPMS warns if pressure diff >30 % (Q-172).
‑ Nitrogen inflation prolongs life (Q-163).
‑ Wheel types: disc, split, wire; split wheel = two clamped discs (Q-127).
‑ Servicing: camber-check shown (Q-130).

BRAKING SYSTEMS

• Hydraulic brake obeys Pascal’s law (Q-202) $P<em>1=P</em>2$.
• Master cylinders – single, tandem, centre-feed. Brake pedal free-play $6\text–12\,\text{mm}$ (Q-224).
• Power assist
‑ Vacuum booster, air-suspended, electro-hydraulic. Vacuum assisted schematic Q-221.
• ABS slip-ratio $=((V<em>{veh}-V</em>{wheel})/V_{veh})\times100$ (Q-207).
• EBD – balances rear-wheel pressure, lamp indication on dash (Q-231/228). G-sensor measures deceleration (Q-226). TCS/ELSD adjust engine torque (Q-229/230).
• Proportioning valve prevents front lock (Q-222).
• Brake lining materials: semi-metallic (steel-wool, Q-213), organic (resin binder, Q-214), carbon-carbon for racing (Q-212).
• Drum components – shoes, hold-down pin, retract springs (Q-203/218). Slack-adjusters for S-cam (Q-210/211).
• Permitted pedal travel: hydraulic system 7-12 mm (Q-215).
• Troubleshooting – low pedal: air, leaks; hard steering noise hydraulic: air in fluid (Q-175/176).

ELECTRICAL – IGNITION & EFI

• Ignition system: battery-coil, distributor, breaker, condenser. Faraday’s law governs EMF (Q-276).
• Distributor functions – time & distribute HT to plugs (Q-289). Condenser suppresses arcing (Q-290).
• Centrifugal / vacuum advance mechanisms parts (Q-286/287).
• Spark-plug gap ≈$2.03\,\text{mm}$ (Q-284), checked with feeler gauge (Q-279). Long heat path → hot plug (Q-293).
• Firing order 4-cyl: 1-3-4-2 (Q-272).
• Sensors
‑ Crank / Cam position (Hall / magnetic) (Q-277/280).
‑ MAP/Mass air-flow in intake; O₂ sensor in exhaust (Q-304/305).
‑ Knock, temp, TPS, blind-spot, parking etc.
• Engine Control Module (ECM) regulates fuel, spark, idle; Idle speed control prevents stalling (Q-295). ECU types: PCM = ECM+TCM (Q-445); BCM – body; VCM – vehicle (Q-444-447).
• EFI advantages – better start & acceleration, precise mixture (Q-312/300).
• Cold-start: thermo-time switch, auxiliary air valve (Q-310/313).
• Radiator fan on/off below 98 °C / 93 °C (Q-273).

CHARGING & STARTING

• Heavy-vehicle system voltage 24 V.
• Alternator – electromagnetic induction (Q-335); converts AC via silicon diodes (Q-338) to DC, regulated by voltage-regulator (Q-354). Low output reasons – faulty regulator, loose belt (Q-361-364).
• Starter motor – 12 V series-wound DC giving high torque (Q-324/349). Bendix / over-running clutch drive; pinion must disengage to protect motor (Q-350). Minimum crank rpm ≈100 (Q-347). Armature leads soldered to commutator (Q-351).

AUTO-LIGHTING & ACCESSORIES

• Headlamps – halogen provide +25 % over sealed-beam (Q-375); LED fastest bright (Q-376). Gas in sealed-beam = Argon (Q-370). Dip/dim switch in head-light circuit (Q-385).
• Indicator colours: front – white, rear pilot – green, tail – red etc. (Q-365-372). Cornering lamps light blind spot (Q-374).
• Horns – air, bulb, electric, wind-tone. Electric horn faults: fuse blown, stuck relay, tone-disc etc. (Q-432-434). Horn relay shown Q-411.
• Wipers – electric most common (Q-431); current draw 2.7-3.4 A (Q-428). Heavy vehicles may use compressed-air wipers (Q-430).
• Power windows – BCM controlled; lock-out switch for safety (Q-436). Glass not lifting – defective regulator (Q-437).

HVAC & AIR-CONDITIONING

• Refrigerant R-134a boils at $26.5^{\circ}\text C$ (Q-392).
• Main parts: Compressor (Q-386), Magnetic clutch (Q-387/400), Condenser (cools hot vapour, Q-401), Receiver-drier (moisture absorber Q-402), Expansion valve (Q-389/394), Evaporator (removes cabin heat Q-403), Blower.
• Ambient temp sensor behind grille monitors outside air (Q-406/407).
• Airflow modes – Recirculation for dusty outside (Q-404).
• Servo-motor (5 V) positions blend doors; contains DC motor, reduction gear & position sensor (Q-395-398).
• Performance test – airflow ≥8 kg/min (Q-393).

SAFETY & NETWORKING

• Air-bags use accelerometer sensors (Q-415); inflator module mounted in steering wheel (Q-416). System self-check – warning lamp flashes then off at start (Q-424). Inflator fires in ms to protect occupants; seatbelt pretensioners tighten simultaneously (Q-423/425).
• Immobilizer prevents engine start without authorised transponder key (Q-427/438).
• GPS = Global Positioning Satellite (Q-414). ICAT = Intelligent Computerised Anti-Theft (Q-417).
• Multiplex networking lowers weight/cost; enables vehicle tracking (Q-420/451). Triangulation locates vehicle using ≥4 satellites (Q-421).

MOTOR-VEHICLE ACT & FORMS (India)

• Motor Vehicle Act enforced 1 July 1989 (Q-232).
• Licence ages – transport 20 y (Q-234); learner validity 6 months (Q-235); transport licence 3 y (Q-236); non-transport 20 y (Q-237); International permit 1 y (Q-238).
• Vehicle categories – Maxi-cab carries 6-12 passengers (Q-233).
• Dimension limits rigid 2-axle goods: 12 m length, 4.2 m height (Q-240/246).
• Traffic signs: red circle = prohibition (Q-247); narrow bridge, school, etc. (Q-239-243).
• Key Forms
‑ Form-1 physical fitness; 1-A medical; 9 licence renewal; 20 registration; 26 duplicate RC; 30 ownership transfer; 33 change address; LLD loss of DL; CF-Sub temp auth when fitness lapsed. (Q-244-253).

TROUBLESHOOTING QUICK-TABLE (selected)

• Low oil pressure – worn crank/cam bearings (Q-256) or clogged strainer (Q-257).
• Engine erratic – water in fuel (Q-262), air leak induction (Q-314).
• Overheating – loose fan-belt (Q-260), carbon deposit piston (Q-264).
• High fuel use – clogged air cleaner (Q-268).
• Hard cold start – faulty thermo-time switch (Q-315).

FORMULA & DATA BOX

• ABS Slip ratio $\displaystyle SR=\frac{V<em>{veh}-V</em>{wheel}}{V_{veh}}\times100$.
• Battery voltages – light vehicles $12\,\text V$, heavy $24\,\text V$.
• Clutch pedal free-play $6\text{–}10\,\text{mm}$; Brake pedal free-play $6\text{–}12\,\text{mm}$.
• Steering ratio (pitman twice steering arm) $=1{:}2$ toe geometry (Q-98).
• Spark plug gap $\approx2.0\,\text{mm}$.
• R-134a boiling point $26.5^{\circ}\text C$.

ETHICAL / LEGAL / PRACTICAL NOTES

• Labour Acts – Workers Compensation 1923 (accidents, disability), Payment of Wages 1936.
• Manuals – Owner, Shop, Repair, Labour guide each serve different data (Q-441-443).
• Safety systems (air-bag, seatbelt) must never be reused post-deployment; diagnostics via scan-tool codes (3-digit, 9 = I/O & controls; 6 = computer system).