No on-board diagnostics
Many old cars have no control unit to give you a fault code. The cause is found by inspection, testing and the wiring diagrams.
Common faults
Common faults
Old cars have recognisable ailments: corrosion, unreliable contacts, carburettor quirks, leaks from hardened rubber. This section helps you link a symptom to a possible cause; the repair procedure for your model is set by the workshop manual and a specialist.
The ailments of old cars
| Symptom | Possible causes | Where to start |
|---|---|---|
| Rust spots, bubbling paint | Moisture in hidden cavities, blocked drain holes | Inspect the sills, arches and underbody; assess whether structural parts are affected |
| Instruments or lights not working, intermittent faults | Corroded contacts, poor earth, old wiring insulation | Check terminals, connections and earth points; inspect the wiring |
| Uneven idle, hesitation when accelerating | Dirty carburettor, air leak, adjustment off, ignition | Check for air leaks and the ignition system, then the fuel side |
| Oil or fluid leaks, water in the cabin | Hardened oil seals, gaskets, hoses and weatherstrips | Find the leak on a clean unit; inspect the rubber parts |
| Brakes pull to one side or lose effectiveness | Old hoses and seals, moisture in the brake fluid | Do not drive until a specialist has checked the braking system |
How to trace the cause
A general approach that works for most old cars.
Describe the symptom
When it appears, what makes it go away, whether it depends on the weather and warm-up. The more precise the description, the fewer unnecessary replacements.
Rule out the simple things
Battery terminals, fuses, fluid levels, connectors — on old cars many faults start with a poor contact.
Work through the system
For the engine — ignition and air leaks first, then fuel delivery. For electrics — from the source to the consumer, following the wiring diagram in the manual.
Change one thing at a time
If you replace several parts at once, you cannot tell what helped. This is especially important when adjusting a carburettor.
Check the documentation
Take adjustment values and dismantling procedures from the workshop manual and catalogues for the model, not from second-hand accounts.
What sets old cars apart
Age matters more than mileage
Rubber, wiring and fluids age even at low mileage. A car that has stood for a long time may need more attention than one that has been driven.
Traces of previous repairs
Home-made wiring changes or non-standard parts make fault-finding harder. Compare with the factory diagram and catalogue.
Sources
- Factory workshop manuals and wiring diagrams
- Parts catalogues for specific models
- Trade publications on running classic cars
This reference covers the history of automotive engineering and general principles. Take service schedules, capacities, torque settings and component specifications for a particular model only from the factory manual and parts catalogues. Check registration rules and the rules on modifications with the official authorities.