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How the Model T Transmission Works
So lets look at how everything works, remembering these
simple rules:
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Each of the Triple Gears does exactly the same as the
other
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The driven gear and therefore brake drum always do
whatever the car is doing, be the car stationary, going forwards or in
reverse.
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The clutch is only used in direct drive (high gear)
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The Triple gears are only used to drive in low gear and
reverse.
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The low speed drum and reverse drums spin unless clamped
by the pedal bands.
With the engine running and the car standing still the
following happens:
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The car is stationary, which means the driving plate is
stationary because it is permanently fixed to the driveshaft and rear axle.
The reason the engine can still run is because the link follows this:
Driveshaft, driven plate, brake drum, large clutch discs and driven gear are
all stationary. (remember the driven gear spins freely on the transmission
shaft, so when its still, the shaft spins inside it) because they are all
joined together.
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Flywheel, transmission shaft, clutch disc drum, small
clutch discs all spin, because either the emergency brake lever or the
driver (via the low speed pedal) is holding the clutch spring pressure off
the discs, allowing the large to be stationary and the small to spin with
the clutch disc drum and small discs.
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All drums can, and to some degree will, spin when the
car is in neutral, unless held by the bands when a pedal is depressed.
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Simulator Instructions
In the Simulator, the gears that are attached to the drums are shown only as
an example of the number of gear teeth, action and direction of rotation when a
gear is selected.
Low Speed
When the driver wishes to move off (forwards), the emergency brake is released
halfway (to allow the rear wheels to turn), but still preventing the clutch
spring to clamp the discs together. (obviously you can't just "drop" the car
into high gear as it would stall the engine - although this is physically
possible
The driver pushes and holds the low speed pedal down whilst altering the engine
speed to compensate. This clamps the low speed drum and gear still. Because
there is a difference in gear teeth between the low speed gear and meshed triple
gear teeth, the triple gears turn on their axis at a slower rate than the
flywheel and in turn rotate the driven gear in the same direction as the
flywheel also at a slower rate.
Because of the difference in gear size between the low speed drum gear and
meshed low speed triple gear, the driven gear is forced in the same direction as
the flywheel at the same slower rate. Remember the driven gear is locked to the
brake drum and therefore turns the brake drum and driven plate (remember its
bolted to the drum) and therefore the driveshaft at the same reduced rate.
Click on the handbrake in the Simulator, then click on the low speed pedal
and see what the gears do.
Reverse gear
When the driver wishes to move in reverse, the emergency brake must be released.
The emergency brake is released halfway (to allow the rear wheels to turn), but
still preventing the clutch spring clamping the discs together.
The driver pushes and holds the reverse pedal whilst altering the engine speed
to suit. This clamps the reverse drum and gear still and forces the driving
motion through the meshed triple gear to the driven gear.
In this instance, because the difference in reverse gear teeth and triple gear
teeth is 30 teeth on reverse and 24 on the meshed reverse triple gear, the
triple gear turns faster (6 extra teeth for each revolution of the flywheel on
its own axis.
The triple gear meshed with the driven gear will also do the same and force the
driven gear in the opposite direction.
Click on the handbrake in the Simulator, then click on the reverse pedal and
see the changing gear speeds.
High Speed Gear
when the driver wishes to engage high gear (direct drive), the emergency brake
lever must be released fully forward (whilst the low pedal is either held
halfway or fully depressed engaging low gear) so that it no longer prevents the
clutch spring from compressing the clutch discs. As the car speed is increased,
ready to shift to high gear, the driver momentarily lowers the engine revs and
simultaneously releases the low gear pedal (and therefore the last resistance
holding the clutch spring back), this allows the clutch spring to apply full
pressure to the discs, clamping the small discs between the large discs. Now
remember that the small discs are directly fixed to the disc drum and therefore
transmission shaft and flywheel, and, the large discs are fixed to the brake
drum and therefore driven plate. So the action of clamping the two together,
provides a direct link as follows:
Flywheel to transmission shaft, to clutch disc drum to small clutch discs to
large clutch discs to brake drum and driven plate to the driveshaft and rear
axle.
Click on the handbrake to put it in the fully forward position and then click
on the low/high speed pedal to engage high gear; and see the gears in direct
drive.
Transmission Brake
When the driver wishes to stop (without stalling the engine), either the
emergency brake lever or low speed pedal must be changed, handbrake pulled back
or pedal pushed halfway to release the clutch spring pressure off the clutch
discs and freeing the direct connection between the engine and rear axle, then
(or simultaneously) apply the brake pedal.
This clamps the brake drum and because of the direct connection with the driven
plate, slows the vehicle down to a stop.
The brake can be applied to slow the car without altering the handbrake lever,
but only to a point before the engine stalls. For the purpose of this
explanation, we will disengage the clutch and apply the brake.
Click on the handbrake once to disengage the clutch, then click on the brake
pedal and see the action on the driven gear
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