What is an Overdrive Unit?

Simply, it is an additional gearbox using a planetary gear cluster mounted after your standard gearbox. Overdrive is usually engaged by an electrical solenoid, which allows clutchless gear changes. But its primary purpose is to lower the engine’s revs when cruising at speed.

Which given today’s fashion for high-geared cruising on motorways means any classic that is ‘overdrive-equipped’ is much-prized amid the classic car fraternity. They were used in sports cars such as Ferrari, MG, Healey and Triumph TR, saloons such as Rover, Sunbeam, Jaguar and Vauxhall, and commercial vehicles such as Land Rovers and Ford Transits. Possibly the final cars to be offered with overdrive instead of a five-speed gearbox were the Volvo 240 and 260 series from the 1980s.

What goes wrong with them? They share the same oil as the gearbox. So, they wear similarly, but can also suffer electrical faults.

If your overdrive doesn’t work, is slow to engage or disengage, thumps going into gear, makes noise or has any other fault, get in touch with Project Shop straight away. We can rebuild overdrive assemblies and ensure your high-speed cruising is comfortable and quiet.

Share This