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The Dennis Patent Automatic Clutch and Easy-Change Gear
by Tim Stubbs

In February 2002, the Owners Newsletter carried a copy of a 1932 advertisement for an Automatic Clutch / Easy Gear-Change - available on new chassis for an extra £40. This was a little-known Dennis product, even amongst ardent enthusiasts, and it was only when Gerry Bixley came up with his researches, we were able to answer the question "what was this?"
“This”, it turns out, was an electro-vacuum operated device which was worked by the driver using a push button beside the pedals. The gearbox was fitted with an additional dog-clutch at the output end, no doubt similar to the dog clutches with shaped teeth as used in the overdrive part of the normal 5-speed Lance/Lancet gearboxes. The operation of the special push button activated a solenoid which in turn used a vacuum piston arrangement (similar to a vacuum brake servo) to operate the 'Easy-Change' mechanism.

On pressing the button, the vacuum piston rapidly disengaged the normal clutch, the additional dog clutch and operated the existing clutch-stop, this stopping the rotation of all the gearbox shafts. The driver was then able to select any desired gear with the gearbox stationary and, on releasing the button, the dog clutch and then the main clutch were gradually re-engaged. Dennis publicity claims - "It's so simple!" and refers to the "sub-conscious mental strain which is probably the greatest contributor to fatigue in drivers" who have to change gear by the old-fashioned double de-clutching method! Or was it a way forward to compete with other manufacturers who were developing fluid flywheels and epicyclic gearboxes to make the driver's work easier.

It was undoubtedly an ingenious piece of Dennis design but the general lack of information about the "uncanny" gadget suggests that the idea was short lived, possibly even unsuccessful. Can any of our more senior members shed any further light on the system? Has anyone ever heard of one in operation? It would be interesting to hear.

Click on drawing to see an enlargement
Click on drawing to see an enlargement

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