Double Declutching, why double declutch?? (1 Viewer)

[Zozo6969]

Hi guys I drive manual and when I'm bothered I double declutch (dump clutch>neutral>drop clutch>blip throttle>dump clutch>change gear>drop clutch). However, sometimes I don't bother doing it twice so I just (dump clutch>change gear and blip throttle same time>drop clutch). It pretty much does the same thing but I just wanna know why the method was always to declutch twice when declutching once has the same effect. People tell me that its because high revs when the clutch is in burns it up and it can damage the pressure springs and all this, but I've always thought that when the clutch pedal is fully in, it doesn't do minimal damage.

Anyone have any answers??

 

[lengy]

I don't really know what you're asking. From what I know about double clutching, the first jab at the clutch is to disengage it and the second is for the actual gear selection so the clutch can match the revs easier or something to promote clutch durability.

 

[Serius]

lol do you drive a 1970's car? if not you dont need to double shuffle. The reason its done is because back in the day, cars didnt have a synchronising thingy, so you had to neutral, hit the right revs then gear up. These days even my car [16years an still going] can change gears with 1 clutch movement...

so to answer your question, there is no reason to do it unless you are driving a classic antique car.

 

[luscious-llama]

lol do you drive a 1970's car? if not you dont need to double shuffle. The reason its done is because back in the day, cars didnt have a synchronising thingy, so you had to neutral, hit the right revs then gear up. These days even my car [16years an still going] can change gears with 1 clutch movement...

so to answer your question, there is no reason to do it unless you are driving a classic antique car.

He's completely correct I can verify because my dad used to have to double clutch back in the 60s in some of his cars. The synchromesh trans synchronises with the speed of the gear box with that of the engine I think. Basically to my understanding you double clutch in when you're driving in slippery conditions so eliminating braking/skidding. You probably know already that double clutching gives a smoother ride... Oh and it saves a bit of wear/tear on the gearbox

 

[Zozo6969]

Yeh even though you dont need to do it cuz of synchros i still do it just because its smoother and it sounds good when u downchange and you hear the pre-rev. I'll rephrase the question:

Does revving the car with the clutch pedal fulling in do any damage to the clutch?

 

[blue_chameleon]

Does revving the car with the clutch pedal fulling in do any damage to the clutch?

No.

 

[Zozo6969]

What about at friction point with accelerator?? whats the difference

 

[blackkatz]

Sorry for asking a stupid question, but i get confused a lot...
What do you mean by 'dump-ing the clucth'? Do you press the pedal when you said so?

Really, pls help me, any1?
I can barely understand what the guys're talking bout here
Thx

 

[CieL]

He's completely correct I can verify because my dad used to have to double clutch back in the 60s in some of his cars.

*Very off topic*

But... Daymmmmmmm my parents were born in the 60s

blackkatz: To dump... yes, you press down on the clutch... you know, the pedal on the very left in a manual car... did I confuse you there? To drop... you release the pedal back into it's original state...

 

[ToO LaZy ^*]

ermm..dumping the clutch and dropping the clutch mean the same thing i thought..:confused..

 

[synthesized]

What about at friction point with accelerator?? whats the difference

when you slip the clutch there is friction between the flywheel and the clutch. (when it the clutch is fully engaged or disengaged there is no friction). so slipping the clutch makes it heat up faster than normal, which causes it to wear out quicker. of course you have to slip it to match speeds but for most cars it is advisable to do it reasonably quickly.

 

[CieL]

ermm..dumping the clutch and dropping the clutch mean the same thing i thought..:confused..

Just putting in ref to zozo's post so blackkatz can understand what zozo was talking about

dump clutch>neutral>drop clutch>blip throttle>dump clutch>change gear>drop clutch

Unless I misinterpreted something? Then it'll be my bad

 

[loquasagacious]

Clearing things up abit:

Everyone should blip the throttle all the time on downchanges this brings the engine up to drivetrain speed and reduces stresses on the engine/flywheel which increases lifespan and makes the change smoother. Smoothness is a big part of speed. To do this blip under brakes you will need to be able to heel-toe.

Double-de-clutching adds some time to the change. It gives the gearset a couple of seconds to slow down which means they engage smoother. It is slower though. Synchromesh is a technology which allows the gears to engage smoothly without the need to double-de-clutch(DDC). Though DDC-ing does still make the change smoother the change is not as great. Generally speaking the only time that DDC-ing is used is when driving an older car, when driving a car on which the synchros have worn out and in trucks which do it to lengthen lifespan.

DDC-ing is not something race drivers do. A racecar driver doesn't have to worry about wear and tear like others. They will often flat-change. That is hold the accel down through the change it prevents engine revs dropping and so shaves seconds from lap times.

 

[Dumsum]

I don't get it.

What's different about the state of the car when the clutch is in as opposed to being in neutral? Can't you just keep the revs up while the clutch is in? That's what I do and what I was taught to do by an instructor :\

 

[loquasagacious]

Colli you seemed to contradict yourself saying first doubling is good, then that it caused wear and finally it is just a perception.

The purpose of double-de-clutching is NOT to match engine speed with main shaft speed. The purpose of DDC-ing is to allow the gearset to slow slightly and thus engage more smoothly.

The purpose of heel-toeing is to match engine speed with drivetrain speed thus reducing wear.

Dumsum you are a victim of one or both of the following: poor written expression and/or poor teaching.

The way you write suggests flat-changing (not lifting off the accel while changing) this decreases shift time but drastically increases wear and tear.

For a nice smooth ride you should blip (jab with foot) the throttle on downchanges and should come off on upchanges.

 

[blackkatz]

Another off-topic question:
How do you heel-toe?

Terms like that are simply non-existant where i live. In manuals, we just lift the throttle, apply brakes, dump the clutch, change gears then abuse the throttle.

Also what is meant by engine speed and drivetrain speed?
Again, here we just know how to dump the clutch and abuse the throttle......

 

[petar13]

Engine speed - speed of flywheel and crank (the one measured in rpm's)
Drivetrain speed - speed of driveshafts, wheels, gearbox

Heel-toeing has been explained before. It is the process of using your right foot to depress both the brake and accelerator. Using this procedure you can brake and downshift simultaneously. It is usually only reserved for fast cornering around tracks, where upon downchanging the gear, you blip (explained previously) the accelerator, for a smooth and quick gear change out of the corner. Some older (passenger) cars require you to have clown feet to do this, however most newer cars have close-set pedals, suitable for heel toeing.

Some other things to make you think - At ANY time in which you have depressed the clutch, you are wearing out the (clutch release, I think) bearing. Unless you press the clutch to the very, very bottom of the floor, you are also wearing out the friction plate at the same time. This is exarcebated by any revving of the engine - like flatshifting, at the extreme.

This is why it is recommended you disengage the car from gear when at a stop light (instead of sitting on the clutch) - so that you preserve the life of the bearing and friction plate.

Food for thought.

 

[Serius]

Engine speed - speed of flywheel and crank (the one measured in rpm's)
Drivetrain speed - speed of driveshafts, wheels, gearbox

Heel-toeing has been explained before. It is the process of using your right foot to depress both the brake and accelerator. Using this procedure you can brake and downshift simultaneously. It is usually only reserved for fast cornering around tracks, where upon downchanging the gear, you blip (explained previously) the accelerator, for a smooth and quick gear change out of the corner. Some older (passenger) cars require you to have clown feet to do this, however most newer cars have close-set pedals, suitable for heel toeing.

Some other things to make you think - At ANY time in which you have depressed the clutch, you are wearing out the (clutch release, I think) bearing. Unless you press the clutch to the very, very bottom of the floor, you are also wearing out the friction plate at the same time. This is exarcebated by any revving of the engine - like flatshifting, at the extreme.

This is why it is recommended you disengage the car from gear when at a stop light (instead of sitting on the clutch) - so that you preserve the life of the bearing and friction plate.

Food for thought.

actually it isnt suggested you neutral by the RTA. The reason? because if you need to move for emergency vehicles or to avoid an accident you can move alot faster if your clutch is disengaged than if you were in neutral.

Unless your clutch has a friction point very close to the floor, depressing it is the same as in neutral where wear and tear is concerned.

 

[loquasagacious]

The RTA also says you shouldn't speed...

Also can you read? Presumably so in which case you would have seen petar said that when the clutch pedal is fully depressed and the clutch thus completely disengaged that you are wearing the clutch release bearing (too lazy to look it up but throw-out bearing is springing to mind).

 

[petar13]

(too lazy to look it up but throw-out bearing is springing to mind)

That's the one!

The bearing isn't a big deal ($$-wise), however getting to it is - so once you open up the car to get to it (esp if it's FWD), you'll change everything - friction plate, pilot bearing (if rattly), remachine the flywheel, etc, etc...

Anyway, I wasn't aware of RTA's recommendations - but they're free to pay the $1k it costs to replace everything on the 405, to get to the throw out bearing. I'm being a little facetious, but at the end of the day - it's just a matter of caring for your car.

And in my experience with emergency vehicles, one usually has enough notice to put the car into gear. As to accident avoidance - it is doubtful that the fractions of a second you would gain by keeping the car in gear would make a difference to the outcome - a greater role would be played by the 'native' accelerative power of your car.