As I recall fluid drive came out on Imperials in 1939, with
a three speed behind it. If you believe the Dodge ads from
1941, with that setup there's "no need to touch the clutch
pedal, stay in high without stalling, even in emergency
stops!" "A 'cushion of oil' transmits the power that gives
new smoothness to driving," "airplane fast getaway," etc.
etc.
They came out with the M-3 Vacamatic on Chrysler and DeSoto
sixes in 1941, a four-speed planetary gear transmission
behind the fluid drive coupling with vacuum-electric
controls. However, the 8's used Fluid Drive pushing a three
speed plus overdrive with the low gear blocked. The
electric shift on the integral overdrive allowed "shifting"
without clutching. The Vacamatic was used on 8's in '42.
After the war the semi-automatic M-6 Prestomatic replaced
the
M-3. Though the hydraulic-electric engineering was
superior, the operation was very similar. This was used
behind a Fluid Drive unit [1:1] or Fluid Torque converter.
It is necessary to first engage drive or low range [or
reverse] by using the clutch. The clutch can then be let in
with the car stopped and theoretically does not need to be
used again. [In a test of '41 DeSotos, two cars drove coast
to coast with a display on the roof to count the number of
shifts. The semi-automatic driver only used the clutch
about three times.]
There is no way that any of these version could be
considered automatic, in the sense that no driver control is
needed. The shift within the range [1>2 in low range, 3>4
in drive range] is accomplished by momentarily taking one's
foot off the gas pedal until a click [some would say a
clunk] is heard. Thus the driver has to shift, just with
his/her foot and not hand.
When coming to a stop, the torque of deceleration would hold
the planetary gear in the higher gear. Therefore there's an
"interrupter switch" that momentarily kills the ignition on
deceleration to reverse the torque momentarily.
Passing gear, the lower gear of the range, is accomplished
by flooring the gas pedal, which trips the "accelerator
switch." This works much like the interrupter switch. The
biggest problem is that as you rev up to pass a car, and you
want to be in the higher gear, you must take your foot off
the gas pedal and wait for what seems an interminable time
before you hear the click/clunk.
If you ever get the chance to ride in or drive one of these
cars, you'll find this odd yet extremely reliable unit to be
very interesting.
Even the big time car writers such as Richard Langworth
don't really understand, often confusing Fluid Drive with
"semi-automatic."
--Roger van Hoy, '55DeSoto, '42DeSoto, '66Plymouth,
'73Duster, '81 Imperial, Washougal, WA
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