- First gear, second gear, fourth gear,
sixth, eighth, twelfth gear.
(engine revving)
We're talking about manual transmission.
You probably know the basic idea.
The transmission changes the gear ratio
to make sure you're getting the optimum power
from your engine to the wheels.
When two gears are in mesh,
an almost lossless transfer of power occurs.
In this case, a force is applied to the gear on the left,
which is in turn moving the gear on the right.
For every revolution the left gear completes,
the right gear completes one in the opposite direction
and with equal force.
Pretty straightforward.
What makes gears truly useful though
is when they aren't the same size.
Let's shrink that driving gear down by half.
Now it has to complete two rotations
to move the right gear once.
Well, that sucks.
But wait a sec, the total amount of energy
required to move the second gear one revolution
hasn't changed.
But now the driving gear delivers the same amount of energy
over twice as many revolutions,
meaning it requires half the amount of force
at any given moment.
It's like climbing stairs.
Make the steps smaller and each step's easier,
but you gotta take twice as many.
We've all ridden bikes,
so you know what it does.
But how does it work?
A standard manual transmission
is made up of an engine shaft or input shaft,
and that's the side that comes from the engine.
A drive shaft or output shaft,
that's the side that goes to the drive wheels,
and here, underneath both of those,
is the counter shaft.
And on these shafts are the gears.
- How familiar are you with the gear wars exactly?
- All of this has to do
with getting the right amount of torque to the wheel.
If you like learning about torque,
check out our Science Garage on torque and horsepower.
If you want to know about toque and hose powder,
ask a Canadian.
(speaking in foreign language)
But let's get back to the gears.
- Okay, it was about 754 years ago.
- If I turn the input shaft,
the gear on that turns this counter shaft,
and that turns all of the gears on the output shaft.
But all these gears are moving at different speeds.
When the gears aren't engaged,
they spin freely from the output shaft
because they're not anchored to it.
Only one gear at a time is spinning the output shaft,
and that's because of what is anchored to the output shaft,
these hubs.
Around these hubs are sleeves.
These sleeves slide over the teeth on the gear
and anchor them to the hub to drive the output shaft.
But wait, there's more.
Look at those tiny little teeth.
Matching up those tiny teeth at the edge of our gear
with the sleeves' tiny teeth.
Well, that's almost impossible.
So between them are these synchronizers.
We cut the power to the counter shaft,
let the wheels drive the output shaft for a change,
and when we push the synchronizer ring,
it gets squeezed against our gear
and locks it to the hub,
so it's anchored to the output shaft.
That's why when you're shifting,
you get that uh-uh.
(engine revving)
Now the wheels in the drive shaft and the counter shaft
are all spinning in mesh.
Voila, we've shifted gears.
Some manual five-speed transmissions
may have minor differences here or there.
This is pretty standard for the most part.
The big gear here, which is enmeshed
with the smallest gear in the counter shaft is first gear.
First gear is always gonna be
the largest gear in the transmission,
producing more torque for the back wheel.
It's taking a lot of fast turning force
and making one big slow turning force.
The slightly smaller gear next to that's second.
Then goes third and smallest one's fourth.
On most four- and five-speed transmissions,
fourth gear is what's called direct drive,
or a one-to-one gear ratio,
meaning the input and output
are turning at the same rate of speed.
Okay, let's pop the shift fork into first gear
and engage that big ol' gear here in the front.
In first, this particular transmission's
got a gear ratio of 3.83 to one,
so I can turn the input, one, two, three
in exactly 0.8 times,
and you can see the output has turned once.
That's torque, baby.
Pop it into second,
and the gear ratio on this guy's 2.062 to one.
Third gear is 1.4 to one.
You know the drill.
One and .4 turns turns it one time.
And then as we mentioned earlier, fourth, one to one.
They're turning at the same speed.
That's gear ratios.
Guys, we did it.
(children cheering)
Now a lot of you are probably saying
what about fifth gear?
We're getting there.
Fifth gear is kinda hidden in the back here,
and we call it overdrive.
Remember how first or third gear were high gear ratios?
Well, get ready for a low gear ratio, buddy boy.
In fifth gear, I only need to turn this shaft .8 times
to get a full turn on the output.
That's overdrive, which gets mucho better fuel economy.
At this point, you're getting power
from the forward momentum of your vehicle
and don't need as much power
going to your engine or your wheels.
Some six- and seven-speed cars can have double overdrive
for even better fuel economy at those high, high speeds.
Oh, reverse is over here.
Boop, boop, boop.
It hits this gear, it makes your drive shaft
spin the same direction as your counter shaft.
Now here's the rub.
The drive shaft's attached to the wheels, remember?
When we shift gears, the wheels are gonna want to
spin the counter shaft at a different speed
than the engine's trying to spin it.
We have to take that power off somewhere,
or it'll make a grinding sound,
like when your brother's robot hamster
won't stop body shaming you
so you throw it in the blender
with all the bad forks and spoons
and press puree to teach it a lesson.
So where do we let all that spinning energy go?
The clutch.
The clutch looks like this.
The clutch has a disc
with a high friction material on both sides.
The engine is actually driving the flywheel.
And the input shaft to the transmission
is mounted to the disc.
When the disc is pressed firmly against the flywheel,
it catches and can drive the shaft.
In the case of this clutch,
it's squeezed by these springs
and attached to a pressure disc
and anchored by this pressure plate,
which gets bolted to the flywheel.
Most clutches use three springs,
but in performance clutches you can have more.
And that makes the connection between the disc
and the flywheel even stronger and more effective
in high torque application.
Like racing.
And this is where things get a little tricky.
A diaphragm spring is connected to the pressure disc
under the pressure plate.
When you hit the clutch it pushes the center
of that diaphragm spring and that pulls up on the springs,
which lifts the friction plate off the flywheel.
Awesome.
Now we've disengaged the power from the shaft,
but we let off the clutch pedal
and re-engage the friction disc,
you're gonna bang, pop right into action.
We don't want that.
We want to ease into the movement.
So attached to the friction plate
there's these other plates with coil springs in them.
These springs are attached to a hub
and that plate is the one that anchors the shaft,
and that goes to the transmission.
Those springs absorb the jolt of re-engaging
the friction plate to take a little stress
off the other parts of your drive train.
You want to try to get on
and off your clutch pretty quickly,
or you might burn it out.
(engine revving)
That happens when the flywheel and the friction plate
rub together too much.
It happens.
Usually waiting on a hill to get into a Dodgers game.
(engine revving)
So what is a double clutch?
- Rarely shifting, not double clutching like you should.
- Well, it's not really two clutches.
Double clutch is clutching twice.
Once when you shift into neutral
to hit the gas and match the engine revs
to the gear you want to go into.
Then you hit the clutch a second time
to shift into that gear.
I always use the double clutch when I'm racing,
drivin' big rigs, and dunking.
♪ I believe I can fly, whoo ♪
- Pretty cool.
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You like replacing your clutch,
check out this video on turbos.
You want to hear about a car
with maybe the coolest transmission ever?
Check it out on this Up to Speed on Conigzig.
Don't tell my wife I burned out the clutch
and had to get it repaired, it's expensive.