Modern automatic transmissions are pretty complex things and there’s a lot that can go wrong from the simple low fluid level to the catastrophic like a broken torque converter or failed valve body, gearset, oil pump or clutch pack.

But mechanics know that the first sign of this transmission failing totally is a refusal to select Drive. Take the car to a transmission specialist who will have seen these symptoms before and will have a pretty good idea of what’s going on before they even lay a spanner on the car. And be prepared to replace the transmission as the only proper fix.

A second-hand transmission from a wrecked Commodore might be an option, but only if you can prove that the unit has done moderate mileage and, therefore, is probably not about to produce the same symptoms as yours already has.

Presumably the car makes this noise when you hit a bump or undulation. The Commodore’s front end is not particularly complex and is, in fact, a pretty standard MacPherson strut set-up.

With that in mind, there are only so many things that could cause the front end to bang or rattle, including a worn ball-joint, tie-rod end, or suspension bush. But don’t forget about the bushes in the steering rack, too, as these can contribute to a noise from the front end.

If all the suspension checks out, then you need to go a bit deeper into things like the cross-member mounts, engine mounts and even wheel bearings. Any wear or play in these components will cause a clunk in the right circumstance.

If none of that helps then you need to look beyond the suspension and into areas like a loose battery tray in the engine bay or even a loose piece of trim or sheet metal somewhere on the car. Exhaust heat shields are prime candidates for this, as are the metal shields at the back of each brake disc.

An automatic gearbox relies on fluid pressure as well as volume to make everything work as it should. So, if the level of fluid is correct, you then need to move on to the pump and accumulators involved to ensure that the correct hydraulic pressure is being applied to the bands and clutches that actually apply drive to the gears and physically move the car.

Your problem could be something as simple as a worn pump, but it could also indicate internal wear and tear that requires a complete transmission rebuild. A transmission specialist is your best bet. The good news is that this is a common and well understood transmission, so finding an expert shouldn’t be difficult.