Subaru Brumby Gearbox & Transmission Problems

You could have a missing tooth on the differential or some other problem that is leading to the clunking noise. But don’t rule out something like a broken or worn engine or transmission mount, either. These mounts control the movement of the driveline relative to the chassis and wear in them can allow excess movement that can sometimes be heard as a clunk or knock.

You may also have a problem with the suspension. This is a very common source of knocking sounds, caused when something worn or loose has develops enough movement to contact another part of the car or suspension. You could start by checking the suspension struts, ball-joints and bushes for wear and play.

The Brumby had a four-speed manual right to the end. It's possible someone has fitted a five-speed to improve highway performance, but it would have been a private conversion.