Can somebody tell me how to double clutch correctly?
thanks

 

You are not driving an old work truck, nor are you running a non-synchromesh transmission. Why in gods name do you need to double-clutch?

 

the 'fast and furious' is not set in reality!

 

if you have bad syncros in your tranny, you can double clutch to prevent the grinding sound when you downshift.

Its only done when down shifting. I will explain what to do without getting into the details of what goes on in the gear box while you are doing it.

First, you have to know what RPMs your gears are going to be at when you are at a specific road speed. Don't worry, I will use an easy to understand example.

Lets use these numbers as an example. Say when you are at 45 MPH, and are in 4rd gear, you are at 2200 RPMs. At 45 MPH in 3rd gear you are at 3800 RPMs. Here is what you would do.

You are traveling at 45 MPH in 4th at 2200 RPMs and want to downshift (double clutch style) to 3rd. Here is what you do. Let of the gas while pressing the clutch (like normal shifting) and move the stick to nuetral and release the clutch pedal. Now the car will be slowing and the RPMs will be falling off. While in nuetral with the clutch pedal released, rev the gas until the RPMs are at about 4300 RPMs. Now shift from nuetral down to 3rd. While you are shifting, the RPMs will fall, and you should go into 3rd when they are right about 3800. When 3rd gear engages, you should be in its power band for the current road speed, which is 45mph.

As mentioned before, with a transmission that has functioning syncros, you don't need to do this.

To understand better how syncros work, go to www.howstuffworks.com and search for manual transmission. I used to have a link to a site that explained what was going on inside the tranny while you were double clutching, but I don't have it now. Sorry. I could explain it, but I don't have time, I'm about to go to work.

 

A. Old synchros. Not all of us have rebuilt transmissions. Especially when cold, older ones don't work for ****.

B. Large unexpected changes in speed followed by a need for rapid acceleration. An example would be having to slam on your brakes from 50mph and slowing down to 15mph. At this point, you've either clutched, or are WAY out of the power band.
In order to get it into 1st (for mind numbing acceleration), you need about 4000 RPM on the input shaft. My synchros won't go from idle to 4000 RPM - and even if they could, it would be rather hard on them. So, a quick blip of throttle in neutral lets me get back into gear where I want to be.

Theoretically you don't have to double-clutch, and for the most part it's not needed in normal driving, but knowing how to do it can be useful.

-=Russ=-

 

1) push clutch pedal in
2) shift out of gear
3) release clutch pedal
4) rev engine to proper rev "range"
5) push clutch pedal in
6) shift into next gear
7) release clutch pedal

That's the basic gist of it.
There are variation of this, but I think this is the "proper" double-clutch method.


-Ted

 

some cars or trucks if you lightly apply some pressure on the stick in the direction of the next gear from N-
the shifter will drop right into the next gear with no C-
at the correct point when the RPM's are falling.

This is not recommended and should not be tried
at home or anywhere.

 

I know someone who is good enough with most of his cars to drive then clutchless (as adzam7XR explained). If the RPMs are matched just right, you don't need the clutch at all, and it slides right in.

-=Russ=-

 

Why would you need to double-clutch. RX-7's are fast just hammer on the gas and go go go. (Shift when neccesary)

 

clutchless shifting is fun
just need to find the right rev-range

 

See above. To maintain "fast" after having to slow down suddenly. If your synchros can handle a shift to 1st at 15-20mph, more power to them, but a lot of us can't get that to happen without a double clutch.

Plus, it reduces wear on the transmission, and is generally a good skill to have. Required? Nope. Useful? Certainly.

-=Russ=-

 

I don't know about y'all. But the last time I checked my stock TII tranny doesn't have a synchro for first gear. So if you want to go into first above 5mph you just have to shove the b in there.

- Steiner

 

ohhhh.... i thought f&f actually did make that up. LOL

i've been doing that as long as i've been driving--with the exception of i don't take my foot off the clutch. my feet are too big and i'm too clumsy for heel-toe, so i just tilt my foot a little bit and hit the gas from the side.

i even do it with no clutch at all! mine doesn't work very well right now so i only use it for starting and hard braking when i have to downshift fast. :p

 

f&f made up the fact that it has street racing applications. the only application of double clutching that makes sense to me is if ur slowing to a stop. I see many people do this automatically, simply because it prepares them to waiting at a light. now why can't one press the clutch in and then drop it into first and simply wait for the right speed/rpms and then release the clutch?

 

This is going to get complicated to explain, since you asked......

Its all got to do with the gears and shafts in the transmission. There are 2 shafts. The main shaft, with all the forward gears (1-5) and then the countershaft, which has gears that are matched to the forward gears. When you are in Nuetral, all the gears are free-wheeling on the shafts. The shafts will spin faster when you rev the gas in Nuetral. When you move the stick to 3rd, you are moving a coupler into that gear to lock it to the shaft. This gear now determinds the tranny output ratio.

So, when you are in 3rd and want to go down to 2nd, the road speed becomes a factor because the rear diff and the tranny output shaft are rolling at the same speed. You can just hold the clutch and down shift, but the 2nd gear will be rotating way faster for that specific road speed (MPH) so the syncro will match the gear speeds and road speed as you are shifting. This defeats the need to double clutch.

When you double clutch, you go to nuetral and let the clutch pedal out. Now remember I said that all shafts and gears will spin when you rev the gas in nuetral. Rev the gas to the RPM you will need the engine to be at for that specific gear and that specific road speed. Now you will shift into 2nd and the all the speeds (road speed, engine/tranny RPM) will be the same and the gears will mesh without the need of the syncros to speed everything up.

This only works for downshifting because when you up shift, say from 3rd to 4th, the 4th gear is a bigger gear, so it is spinning slower at the specific road speed, so the syncro doesn't need to speed the gear up before the engagement.

For illustrations of the inside of a manual tranny, click here

 

when i'm tearin' *** up a windy road and have to slow down REAL quick for a turn, it help to match the rpm i will be at when i downshift--to keep the back wheels from chirpin' and losing the *** and flying off a 200 foot cliff. it makes the downshifts smoother.


but with 200k+ miles on the last tranny, it didn't like downshifting

i know engines pretty well, but this is a really informative thread cu i don't know jack about trannies. thanks for all the info!!

 

actually, my 5th gear synchro is out. so, i have been double-clutching to get into 5th gear pretty much for the entirety of my driving experience with my 2nd gen turbo. if i dont double-clutch, then i just grind the hell out of it until it decides to jam in. since i am not too keen on screwing up my 5th gear, i simply double-clutch it to upshift into 5th. so, you may also double-clutch to get into a higher gear, if your synchroes are shot. take it from experience from a guy with a ragged tranny (for now).

 

There is a common misconception that double clutching means this: If you are accelerating quickly in 1st gear and then shift into second hard but then push the clutch in with your gas foot floored and then release the clutch. It's supposed to boost your acceleration, but i think it just f's up your clutch

 

I learned that in my GTi, never ever been able to use it usefully but its fun for show

 

Yea clutchless shifting is a neat little trick. My friend was awe struck and said How did you do that? I simply explained that when the gears are spinning at the proper speed they like to join with each other, so you don't need the clutch.

 

Why would you want to double clutch on acceleration?? That makes no sense to me at all. If your synchros are so shot that you feel you need to double clutch on accel, get off the pedal a little bit, just granny shift and help your tranny last a little while. In other words, quit driving like a jerk.

In all fairness, I double clutch one of my vehicles all the time, my 1953 chevy truck.

 

it is alot easier to upshift on the synchos than downshift....
it doesnt have to spin the inputshaft and the clutch up to a higher rpm... just need to slow it down

on my tranny, i always have to do it on my downshifts or it makes that sound and you coudl feel the gear grind at the shifter....

if i do it, it just slides in smoothly

by the way, great explaination, project 84