What the hell is double clutching?

Paul Perreca · May 2, 2005

I heard this in the movie TFATF - and i always wondered what it was - i fugured id use common sense and figure you hit the clutch pedal twice or somethin lol what is it!
Paul Perreca

cheddarbacon · May 2, 2005

not van

First off its not van diesle hes a douce bag double cluthing for instence the duck boats used a old tranny that had like 14 gears and olny like 7 slots for the stick i dont know exaclly how it works all i know is i went on a duck boat before double clucthing is not used today (uslllay) unless you have a ****y ass car

tjm73 · May 2, 2005

You're pretty much right on the money. Double clutching is used mostly in heavy trucks and some antique cars. It's definitly not high performance.

Basically it goes like this. Let's say you are already accelerating in first gear...

- push in clutch, pull shifter in between 1st and 2nd
- let clutch out, push clutch in and pull shifter into 2nd gear
- repeat up through the gears
- repeat in reverse down through the gears

Now if you're heavy truck has a 2 speed rear axle there is yet another step that you go through (basically pull a knob and push the clutch in again without movingthe shifter), but you didn't ask about that so I don't want to confuse things.

Michael Yount · May 2, 2005

Many of the old transmissions didn't have synchromesh. So you had to try and match engine speed to gear speed in order to get the gears to mesh without crunching a lot.

In order to do that, you do what tjm describes above on upshifts. When you pause in neutral, and let the clutch back out, you slow the tranny down a bit, which makes the next higher gear easier to select/mesh.

The procedure is different on downshifts however. On a downshift, you need to speed the tranny up in between gears. So when double clutching on a downshift, you would actually blip the throttle while the shifter is in neutral and the clutch is back out. This spins the tranny up in speed so that, for example, when going from 4th to 3rd, the gears would engage.

It all became unnecessary when synchros came along. Only due to my advancing years do I know anything about it.

True story. My dad as young non-comm in the Army was trying to teach a young Lt. how to drive an old duece and a quarter truck. No synchros on the gears - so double clutching was required. As the young Lt. made terrible crunching noises while trying unsuccessfully to shift the tranny, dad said "It'll help if you double clutch..." The young Lt., who'd obviously been burned before replied "You can't fool me Sarge; that other pedal is the brake!!!"

True story.

Michael Yount · May 2, 2005

With a little experimentation, you can sort of get a feel for what it was like by shifting without using the clutch at all. Wind first out to about 2500 rpm, then when you ease off the gas pull it out of first (no clutch), and just apply steady pressure into second. When the gear and engine speeds match, it'll lightly 'clunk' into the next gear. You should be able to do that all the way through the gears. Same is true downshifting - but you have to blip the throttle in neutral and then apply a little force into the next lower gear. When the engine speed is dropping back down from the 'blip', as soon as the engine and gear speeds match, it'll drop into the next lower gear. It works better on higher mileage trannys where the gears/synchros have lots of wear on them.

tjm73 · May 2, 2005

Michael Yount said:
True story. My dad as young non-comm in the Army was trying to teach a young Lt. how to drive an old duece and a quarter truck. No synchros on the gears - so double clutching was required. As the young Lt. made terrible crunching noises while trying unsuccessfully to shift the tranny, dad said "It'll help if you double clutch..." The young Lt., who'd obviously been burned before replied "You can't fool me Sarge; that other pedal is the brake!!!"

True story.

I love those funny ol' Army stories.

TheUser · May 2, 2005

cheddarbacon said:
First off its not van diesle hes a douce bag double cluthing for instence the duck boats used a old tranny that had like 14 gears and olny like 7 slots for the stick i dont know exaclly how it works all i know is i went on a duck boat before double clucthing is not used today (uslllay) unless you have a ****y ass car

You'd say whatever they told you to too if you were getting paid a few million bucks to do it. The writers made up those lines, not the actors. I like Vin Diesel.

And I've tried shifting w/o the clutch before just to learn how...easier said than done. I don't know if it's just incompetence or the fear of breaking my tranny...

Michael Yount · May 2, 2005

User - yeah - you have to have a certain confidence about it. It's as if the tranny has an anxiety chip in it -- and if you try it without the clutch without full confidence that you know what you're doing, it'll bite you.

I used to wow my buddies by going all the way up and back down through the gears with no clutch. 'Course, that was in a vehicle with a 120k on it - those synchros/gears were smooth as a baby's behind - I could shift it just as smoothly with or without the clutch.

crazypete · May 2, 2005

I sorta figured that out on my own through experimentation.

I was driving around speed matching and I was able to pull the transmission through gears with no clutch. 5th needs clutch and downshifting was a no-go but I could get the car to just glide down the road otherwise. When I hit 2500 rpm, I pull it out of gear and apply some pressure to the next gear. Around 2k rpms as the rpms fell, it would slide into the next gear. The key is to be really light throttle. Think coasting. You cant be accelerating when you do this. My t-5 had no synchro left so this was half for fun and half necessity.

BlackGT89 · May 2, 2005

Michael Yount said:
I used to wow my buddies by going all the way up and back down through the gears with no clutch. 'Course, that was in a vehicle with a 120k on it - those synchros/gears were smooth as a baby's behind - I could shift it just as smoothly with or without the clutch.

Yep, this method is also useful if you have to get a car home after the clutch cable has broken. Only problem arises if you have to come to a stop in heavy traffic, then you have to cut the key off and stop when the light turns red and then start it in gear when it turns green. Not good on the equipment but only useful as a last resort (no flames please). It also worked a lot better on my old German Capri V6 with a four speed than it does on my GT.

No need to double clutch on modern trannies.

Michael Yount · May 2, 2005

Pete - it'll work for downshifting too - just remember to blip the throttle when you're in neutral - just as the revs have to drop from 2500 to 2000 on an upshift, they have to RISE from about 2000 to 2500 on a downshift.

I_AM_CANADIAN · May 2, 2005

BlackGT89 said:
Yep, this method is also useful if you have to get a car home after the clutch cable has broken. Only problem arises if you have to come to a stop in heavy traffic, then you have to cut the key off and stop when the light turns red and then start it in gear when it turns green. Not good on the equipment but only useful as a last resort (no flames please). It also worked a lot better on my old German Capri V6 with a four speed than it does on my GT.

No need to double clutch on modern trannies.

I had to do this when my clutch cable broke in my truck. It was...... interesting.

Nobody · May 2, 2005

Back to the original question - I have herad that some of the low displacement guys "double clutch" under power to get revs up to get the car moving faster. Sorta llike the small engine class carts - they hop up and down in their seats to get the weight off the cart to accelerate faster.

Not sure if it's true or not tho'

Michael Yount · May 2, 2005

I've raced MANY more small displacement cars than big displacement cars. Hopping up and down in the seat would be more effective than double clutching to increase performance - although neither would actually accomplish anything.

On downshifting under braking, many racers blip the throttle (some with double clutching, some without) to match engine speed to tranny speed so that engine compression braking doesn't lock the rear tires while you're trying to set up for a turn. That's a big no-no.

Speeds8erM-1 · May 2, 2005

Paul Perreca said:
I heard this in the movie TFATF - and i always wondered what it was - i fugured id use common sense and figure you hit the clutch pedal twice or somethin lol what is it!
Paul Perreca

Thats why that movie is considered such a joke, stupid lines like that and all the rice, 10 minute long races, akkkkkk.

z9_87 · May 2, 2005

Speeds8erM-1 said:
Thats why that movie is considered such a joke, stupid lines like that and all the rice, 10 minute long races, akkkkkk.

Especially the 10 min races. I'd have topped out my car long ago if I went for 10 mins WOT. Then I really like in the 2nd one when they beat the 2 muscle cars. Kind of funny they couldn't do it without the one the muscle car guy being crappy drivers. Although that race lasted forever also. Did you ever watch the speedo when they showed it. It was like 1mph/min.

RacEoHolic330 · May 2, 2005

Michael.. do you know if there are any long term damages that could occur from clutchless shifting? I used to do that every once and a while, but stopped because I was afraid I'd screw something up.

shonoff · May 2, 2005

I_AM_CANADIAN said:
I had to do this when my clutch cable broke in my truck. It was...... interesting.

HA ha that happened to me too.I had to drive it like that for a couple days.I had to have a friend with me to help push it to get it rolling to get it into 1st......Good times And Paul Perraca--Burn that movie.It has been poisoning the minds of our youth.

jpyjfrdmstng · May 2, 2005

i always double clutched my jeep transmission becuz the clutch wouldnt totally disengage the powertrain, the transmission still works fine, 220,000km later

oohsoobad2 · May 2, 2005

A friend bought the 2Fast2Furious bonus DVD, and in the extra they showed you how to drive like a "pro". The demostrated what they called double clutching and is was what Mustang guys call powershifting, Shifting thru the gears at WOT while using the clutch.

What the hell is double clutching?

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