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Why press the clutch down to change gear?

Why do I need to press the clutch down to change a gear?

I understand that when I press the clutch down I disengage from the flywheel thereby cutting off the power from the motor to the wheels. What does this have to do with changing gears though? :confused:

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Reply 1
Avatar for Camoxide
Camoxide
14
You can actually change gear without the clutch.
Reply 2
Avatar for Steezy
Steezy
15
Cos it makes a ****ing awful sound and feels like the car's gonna break.

Unfortunately that is the most mechanical answer I can give you.
And now you know: http://auto.howstuffworks.com/transmission.htm
Reply 4
Avatar for J1mjam
J1mjam
2
Original post by boo28
Why do I need to press the clutch down to change a gear?

I understand that when I press the clutch down I disengage from the flywheel thereby cutting off the power from the motor to the wheels. What does this have to do with changing gears though? :confused:


When the engine speed and the flywheel speed differ, and dont use the clutch, youll get that horrible crunch sound as the two different discs hit each other. by using the clutch, you separate the gears from the engine. and then slowly engage it back. this allows the discs to get to the right speed slowly. its hard to explain. its possible to match the speed of your engine(its RPM) to gears and change without a clutch. however this requires a very high level of skill.

take a look here for more info http://auto.howstuffworks.com/clutch.htm
Reply 5
Avatar for Camoxide
Camoxide
14
^ it's not that hard to rev match. The gear stick will just slide into the right gear when at the correct revs, it should never be forced.

It's a good skill to have if your clutch pedal goes. Wish I knew you could drive home without the clutch pedal when my clutch cable snapped.
(edited 11 years ago)
Reply 6
Avatar for h-g-1
h-g-1
14
Original post by boo28
Why do I need to press the clutch down to change a gear?

I understand that when I press the clutch down I disengage from the flywheel thereby cutting off the power from the motor to the wheels. What does this have to do with changing gears though? :confused:


The clutch (when pushed down) disengages the engine from the transmission. When that happens, there is no more torque going into the transmission. The transmission contains (very simply) the gearset. So therefore, you can shift into another gear. You then release the clutch and then engine and the transmission are connected again (essentially) and then you can accelerate.

So normally, you get torque from the engine to the clutch which turns shafts that lead into your transmission (where your gears are) which are then engaged and then that force gets transferred to your wheels which is what makes the wheels move. So it's essentially all about the transmission. :smile:
(edited 11 years ago)
Reply 7
Avatar for boo28
boo28
OP
8
Original post by h-g-1
The clutch (when pushed down) disengages the engine from the transmission. When that happens, there is no more torque going into the transmission. The transmission contains (very simply) the gearset. So therefore, you can shift into another gear. You then release the clutch and then engine and the transmission are connected again (essentially) and then you can accelerate.

So normally, you get torque from the engine to the clutch which turns shafts that lead into your transmission (where your gears are) which are then engaged and then that force gets transferred to your wheels which is what makes the wheels move. So it's essentially all about the transmission. :smile:


Thanks, that's a great explanation of what's happening. But I still don't understand why do I need to disengage the engine from the transmission to change the gear. I know that if I don't use the clutch I get a horrible sound, but what's really going on?
(edited 11 years ago)
Reply 8
Avatar for boo28
boo28
OP
8
Original post by J1mjam
When the engine speed and the flywheel speed differ, and dont use the clutch, youll get that horrible crunch sound as the two different discs hit each other. by using the clutch, you separate the gears from the engine. and then slowly engage it back. this allows the discs to get to the right speed slowly. its hard to explain. its possible to match the speed of your engine(its RPM) to gears and change without a clutch. however this requires a very high level of skill.

take a look here for more info http://auto.howstuffworks.com/clutch.htm


Thanks!
Reply 9
Avatar for CurlyBen
CurlyBen
19
Imagine two discs spinning round. Both discs have a hole in, and you have to push a peg through both holes. If the discs are spinning at the same speed you can line the holes up and push the peg through easily. If they're spinning at different speeds its very difficult, the peg gets mangled and you get a horrible noise. That's not quite what happens, in the gearbox you're using dog clutches instead of pegs and discs, but it's kind of similar - both halves of the dog clutch have to be spinning at the same speed for a clean change.


Btw there are some errors (mostly minor) in some of the previous explanations, so don't worry if anything appears contradictory.
Reply 10
Avatar for ROG.
ROG.
6
Many drivers these days do not know how to drive a manual when the clutch pedal fails to work
When I go into 1st gear (or reverse, which is the same place as the 1st gear slot) it makes a horrible grinding noise. Only like twice a month though. It's pretty annoying when that happens.
Reply 12
Avatar for 455409
455409
17
Original post by Camoxide
Wish I knew you could drive home without the clutch pedal when my clutch cable snapped.


Can't think of anything more dangerous. What happens if you need to make an emergency stop? Can't disengage the drive and brakes will be much less effective, even if you stall the engine.

Never ever do this people.
Reply 13
Avatar for Camoxide
Camoxide
14
Original post by james1211
Can't think of anything more dangerous. What happens if you need to make an emergency stop? Can't disengage the drive and brakes will be much less effective, even if you stall the engine.

Never ever do this people.


Just slam your foot on the brakes... The brakes will stop the engine.

You brake quicker with the engine engaged anyway.
Reply 14
Avatar for CurlyBen
CurlyBen
19
Original post by james1211
Can't think of anything more dangerous. What happens if you need to make an emergency stop? Can't disengage the drive and brakes will be much less effective, even if you stall the engine.

Never ever do this people.

If you can't think of anything more dangerous your IQ must be in single digits.
In addition to being wrong about the brakes, gearboxes tend to have a 'neutral' position, don't know if you've heard of it. Also automatics seem to manage, and drive isn't disengaged as such when you brake hard in those.
Reply 15
Avatar for 455409
455409
17
Original post by Camoxide
Just slam your foot on the brakes... The brakes will stop the engine.

You brake quicker with the engine engaged anyway.

With the gear still engaged, especially higher gears such as 4 or 5, the car will start to jerk about and bounce once you drop below its required speed and then stall, and this will all contribute to an increased stopping distance.


Original post by CurlyBen
If you can't think of anything more dangerous your IQ must be in single digits.
In addition to being wrong about the brakes, gearboxes tend to have a 'neutral' position, don't know if you've heard of it. Also automatics seem to manage, and drive isn't disengaged as such when you brake hard in those.


So you're gonna have time to slam it into neutral and brake while coasting before you hit the child that just ran out into the road? I'd rather wait for the AA to come out and replace the cable to be honest.
Reply 16
Avatar for CurlyBen
CurlyBen
19
Original post by james1211
With the gear still engaged, especially higher gears such as 4 or 5, the car will start to jerk about and bounce once you drop below its required speed and then stall, and this will all contribute to an increased stopping distance.




So you're gonna have time to slam it into neutral and brake while coasting before you hit the child that just ran out into the road? I'd rather wait for the AA to come out and replace the cable to be honest.

Frankly I'd just hit the brakes knowing the engine being engaged won't significantly increase the stopping distance.
With the gear still engaged, especially higher gears such as 4 or 5, the car will start to jerk about and bounce once you drop below its required speed and then stall, and this will all contribute to an increased stopping distance
How? Do you actually understand what that jerking is all about?
If the engine stalls in gear how does this increase your stopping distance?
Original post by mphysical
How? Do you actually understand what that jerking is all about?
If the engine stalls in gear how does this increase your stopping distance?


No he doesn't. I bet he thinks that ABS reduces stopping distances too.
My current car is my first with ABS.
The first time I had to stop fairly sharply I was scared it wouldn't stop in time.
Why are my tyres not screeching and why does the pedal feel odd were the thoughts going through my head.

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