Double clutching

Lord Nikon

I've heard about it and want to know more. What is it and how do you do it?

kaimera

http://elecdesign.com/Articles/Index.cfm?AD=1&ArticleID=6137

Let's say you're accelerating in second gear. When you're ready to shift into third, you decide not to use the standard approach, which is just to tromp on the clutch, take your foot off the gas, shove the shift lever into third, and let the clutch back out. Instead, you opt to double-clutch properly:

First, you take your foot off the gas and kick in the clutch. You shift into neutral, AND let the clutch out. You wait perhaps 0.3 to 1.0 seconds for the engine to slow down from its high revs, depending on how fast you were revving when you started to shift and how much inertia the engine has to slow down. THEN you kick in the clutch and shift into third, and let the clutch out quickly, feeding the gas appropriately. If you have judged it right, when you let the clutch out, there isn't any JERK. And when you shove the lever into third, the gears and engine are at a synchronized speed, so there's minimum wear on the synchronizers, which are the tiny clutches that bring the clutch plate and the gears into smooth synchrony. There's also usually less wear on the clutch plates.

What's the big deal? The main point is that when you try to shift into third gear, the engine has slowed itself and the clutch plate down to the right speed—just about the same speed as the gearbox—so it saves wear on the synchronizers and the clutch. It can also save shock and strain on the whole drive-train, because the speeds are just about synchronized when you let out the clutch

Lord Nikon

Thanks for the reply, gonna give a go in the morning after work.

kaimera

let us know how you get on

C_Breeze

eh???
double clutching is used to make the car accelerate faster not waste time and slow down to maintain the syncronization of watever! -at least so i thought.

when youre in gear and anbout to change up you put in the clutch and rev it to to where the amount of revs that gives most power* , you then put into next gear and and release while the you are reving to those revs!

done right it gives a bit of a boost or push when changing gears.


*= itll show this in the car manual eg . 140bhp@5,500rpm


edit: if this is not actually wat double clutching is , i have inveted a new method and it is patented and to be called C-Clutchin' :-p

TempestSabre

My understanding...

It used to be done when gearbox'es didn't have synchromesh. The gears were square cut and it was nigh impossible to go from one gear into the other unless you matched the speeds. These days with synchromesh you don't need to do it.
As for wear, what difference does it make when a normal gear box can do well over a 100k with normal use. In racing cars square cut gears are more common. I think you can change gears faster and theres less power loss than with a synchromesh. Dunno if that still applies though.

SouperComputer

technically its called double de-clutching and is rarely used. It was needed with older cars with non-synchro gearboxes.

The more modern equvilaint is Heel\Toe. Basically when the clutch is on the floor during a normal downchange you use your heel to blip the throttle and match the revs for the next gear before engaging it. It comes in handy on roundabouts, you can drop from 4th or 5th into second without hurting your drivetrain and\or passengers.

Its used in racing to maintain the balance of the car under braking and for mecanical sympathy.

double clutching is used to make the car accelerate faster not waste time and slow down to maintain the syncronization of watever

Thats slipping the clutch, I have heard people call it double clutching for some reason.

With a modern synchro box, the only thing I can think double clutching does is but double the wear on the release bearing!


[edit] jasus, wikipeida really has everything: http://en.wikipedia.org/wiki/Manual_transmission_driving_technique#Advanced_techniques [/quote]

C_Breeze

I still think its what i said
when releasing the clutch instead of keeping your foot off the accelerator , you keep it at high revs and drop the clutch while revs are high.

Capt'n Midnight

Once upon a time cars had straight cut gears and you needed to double declutch to change. Then a French company invented synchromesh gears so you could change more easily. They like the idea so much they used it as their logo. And then everyone started to use it. Only down side is it makes it more difficult to just shove the gear lever across when the clutch is out.

TempestSabre

Quickest way is not to clutch at all. If you match gear speeds you can change up and down without using a clutch. I think they do this in racing. I've only ever done it when a clutch cable snaps. I think you mainly use it changing up and double declutch going down.

I think its called "double declutching" not "double clutching" too.

Again I'm fuzzy on the details and could be talking complete....:)

(Too many people posting at the same time )

SouperComputer

TempestSabre wrote:

Quickest way is not to clutch at all. If you match gear speeds you can change up and down without using a clutch.

It depends on the gearbox. Some will allow you to just lift and change up or down without a clutch, but in a road car with synchro gears not usuing the clutch takes longer.

TempestSabre

SouperComputer wrote:

It depends on the gearbox. Some will allow you to just lift and change up or down without a clutch, but in a road car with synchro gears not usuing the clutch takes longer.

I've only heard of doing it on older (30-40yrs ago) cars or on racing cars. Or when your clutch cable snaps. Which has happened to me in a transit and a old seat ibiza.

fletch

kaimera wrote:

http://elecdesign.com/Articles/Index.cfm?AD=1&ArticleID=6137

I'd agree with C_Breeze on this one....the above method is used to change gear without using the clutch at all....I do it a fair bit as my clutch is near the end of it's life.

JamesM

It is called double de-clutching and "Souper Computer" and "Capt'n Midnight" are correct.

Completely seperately: If your clutch goes, you can start many cars in gear and by getting the revs right you can change up and down gears. I once drove from Kerry to Dublin without a clutch. Another time from Dublin past Blessington and back.
Jim.

Zascar

Its only done when chaing down gears, and usually the lower ones, not necessarilyfrom 5th to 4th, but more like 3rd to 2nd, as there is usualy a bigger difference in the revs. I always use Heel & Toe - I have aftermarket peadles on my car, and the brake and accelerator peadles are quite close together. When breaking I haev the side of my right foot just touching the accelerator - if I am traveling quickly in relativly high revs in 3rd, if I changed normally to 2nd, the wheels are going a lot faster then the engine so the car jerks forward. What I do is brake, and in between changing into 2nd gear, I blip the throttle so the revs rise to match what it will be in 2nd gear. Supercars like Ferrari's with tiptronic (paddle shifters) do this automatically. Makes a cool sound

Lord Nikon

Well, i gave what Kaimera posted a shot, and yes, the gear changes are more fluid. Saying that, it takes longer to gear change, and it's somewhat a waste of time. Gear changes take longer than I would like, and acceleration or de-celeration times are increased. It's interesting though.

Reading some other posts, about changing gears with foot pressed on the accelerator is a no-no. It's pure clutch-burning as it's finest.

Litcagral

TempestSabre wrote:

My understanding...

It used to be done when gearbox'es didn't have synchromesh. The gears were square cut and it was nigh impossible to go from one gear into the other unless you matched the speeds. These days with synchromesh you don't need to do it.
As for wear, what difference does it make when a normal gear box can do well over a 100k with normal use. In racing cars square cut gears are more common. I think you can change gears faster and theres less power loss than with a synchromesh. Dunno if that still applies though.

100% agree. As others posters have said it should be correctly described as "double-declutching". It was particularly important when driving heavy trucks before synchromeshing. It was vitally important to match the speeds or you could miss a gear which could have severe consequences especially when transporting heavy loads in hilly terrain. Some older truck drivers still do it although it is generally unnecessary now. I can't understand why anyone would be bothered doing it in a car though!