Buying a classic car: how to make mechanical checks

Most classics are like big Meccano kits; if you treat items such as the engine, gearbox and back axle as sealed units, you can just swap bits over with relatively little hassle.

The cost of rebuilding these items can be very high though, so get an idea of replacement costs before you inspect your potential purchase. At least the brakes, steering and suspension are usually cheap and easy to sort – but not always, so again, price up any replacement parts before you make any offers to buy the car.

The brakes, steering and suspension are usually cheap and easy to sort
  • Don’t start the engine until you’ve inspected the bodywork and interior, giving it time to cool down if the owner has run it up to temperature before your arrival. Look for bad oil leaks and suspect out-of-balance carburettors if the engine runs unevenly. A worn engine will usually smoke badly, but even the most knackered powerplant can be rebuilt – although costs can be very high if it’s something unusual.
  • Knocking sounds on start up indicate bearing wear, caused by oil starvation, high mileage or hard use. Continuous rumbling signals worn main bearings while clattering from the top of the engine means the valve clearances need adjusting or something (probably the camshaft) has worn. Only the latter means a top-end rebuild; the others mean the bottom half needs reviving – and that’s usually costly unless you just fit a used powerplant.
  • Make sure no water has collected at the bottom of the radiator, signalling leaks; a recore is usually £100+. Get the engine hot (to ensure the thermostat hasn’t been removed) and if there’s an electric fan, make sure it cuts in at the required temperature. Then switch off the engine and try to restart it a few seconds later; hot starting problems can be hard to sort out.
  • On the test drive, if the car has a manual gearbox, change up and down through the gears quickly, to reveal any synchromesh weaknesses. While doing this listen out for any whining from the gearbox and diff; rebuilding these is usually £250+ apiece, although first gear whine is normal on many classics. Check the overdrive works, if fitted; most (but not all) problems are electrical and easy to fix.
  • Clonks as you release the clutch signal that the universal joints on the propshaft and/or the driveshafts have worn out. Replacement is usually cheap and easy, but if there’s a vibration at a certain speed it’s because the propshaft is out of balance; a replacement is normally £100-£150. Also ensure the clutch isn’t slipping; replacement parts are usually cheap but labour charges can increase the cost considerably.
  • Sourcing replacement steering boxes is often tricky, but originals tend to be durable with the possibility of adjusting out wear in most cases – if this has already been done, there might be stiff spots as a result. Steering racks are usually easier to source; they wear through use or because the rubber gaiters on each end have split, allowing dirt in, accelerating wear. Rebuilt racks are £40+; power assistance typically quadruples this cost.
  • The dampers are shot if you press down sharply at each corner and the car doesn’t settle quickly. Leaf and coil springs wear out or break; the latter should be obvious from underneath, but wear isn’t so easy to detect. Look at the ride height; if the car is sitting low at one end or the other it’s time for new springs. Replacement dampers and springs are normally cheap, and they’re easy to renew.
  • Uneven tyre tread wear may show that the tracking is out or it could show more serious problems such as misaligned suspension – especially if the car has been rebuilt. It could also be that the suspension bushes are worn. If the latter is the case, a visual inspection should suffice, but vague steering can also be the result. Also listen for worn wheelbearings; they grumble as you corner.
  • Pressed steel wheels rust, while wires suffer from worn splines and damaged spokes – replacements are typically £75-150 each. Alloy wheels can suffer clearance problems if they’re oversized. Braking systems are usually simple, but servos pack in (so you have to push the pedal harder to stop), wheel cylinders leak and brake pipes corrode. They’re individually cheap to fix, but if it all needs doing the bill could be extra-large.
  • Most classics have simple electrics, but problems can arise from poor earths, dodgy connections and brittle looms. Looms are cheap but fitting is tricky, while sourcing components such as switchgear and instrumentation can be impossible. If any upgrades have been carried out (such as an alternator conversion), make sure the work has been done properly. Also check there’s no chafing anywhere; electrical shorts could lead to a conflagration.