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The ERAS which competed
at Phillip Island and Winton this year caused a great deal of
interest and represent a unique collection of 1930’s motor
engineering. The supercharged six cylinder motor drives
through a Wilson pre-selector gear box and these are somewhat
unusual devices.
The gears are all ( four forward
and reverse ) in constant mesh and each has a break drum with
brake bands. Activation of the band in the drum selects the
individual gear and disengages the other.
The engine is started with the
pre-selector lever in neutral and then used to select first
gear ( or reverse ). Motion is achieved by depressing the gear
change pedal ( similar to a clutch pedal ) and then matching
its release travel with the revs.
Underway, the next gear to be
used is preselected with the lever and engaged by using the
pedal when required. The designer at the time considered this
special box allowed faster changes than with the normal clutch
– gear box combination and avoids missed gear changes which
cause fast revving race engines to over-rev and thus destroy
themselves. As well, having the gear change out of the way lap
times improve as drivers then concentrate on braking and
correcting techniques. All very well, but reliability is an
issue as maintenance requires the service of an experienced
mechanic. As a number of observers noted at the two meetings
“the ERA’S needed total rebuilds between events”.
Never the less, the marque made
its mark in the history of European motor racing and we are
most privileged to experience their grace and pace.
The pre-selector gearbox was
also used in the Lago-Talbot racing cars and the Armstrong
Siddeley and MG K3’s and also the Magnette road cars. Thanks
goes to Bill Prowse for this terminology assistance and
provision of the rare 1930 MG Technical Manual.
- Written by Roger James
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