Over-revving bolt-on unit
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A BOLT-ON unit to prevent engine damage by over-revving has been produced by Martin Transmission Developments. It can be fitted to all buses with semi-automatic gearboxes and electro-pneumatic control systems.
When the box is fitted, reverse gear cannot be obtained above 3mph. Instead, the gearbox reverts to neutral. All the forward gears are available normally up to a predetermined speed for each, which corresponds to an engine speed usually slightly above the governor run-out speed.
If a gear is engaged that would cause the engine to overspeed, the next higher gear is engaged until the vehicle speed falls low enough for the gear selected to engage safely. But once the selected gear is engaged it is held if the engine speed rises above the speed that would prevent its initial engagement. The unit consists of a small circuit box interposed between the selector switch and EP unit, and a probe mounted on the gearbox output shaft to sense the passage of the coupling flange bolts.
The introductory price for 12 is £52 each plus VAT. The company's address is 1 Old Rectory Garden, Alcester, Warwicks.