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Old 07-04-2004, 09:49 PM   #1
VMJYogi
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A (good) question about the double clutch

okay well i know how to do it and everything..... BUt couldn't someone just press the clutch put it in neutral rev the engine to the rpm needed and then put it in gear and release the clutch? why do you have to let it go in neutral just to press it again right away?
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Old 07-05-2004, 03:23 AM   #2
Inygknok
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im gonna give me my best shot, so if i say something wrong, somebody correct me (i would appreciate it if its done in a non-lets-start-a-war-manner).

1) that would be burning the clutch, just like when they tell u to learn how to get the car going without so much clutch playing. in other words, not letting go of the clutch slowly while stepping on the gas a bit hard (like many people do when first learning, that wears out the clutch fast).

2) i dont think u fully understood the whole double clutching thing. u let go of the clutch the first time (after putting it in neutral) so that the engine connects back to the transmission. when u rev the engine at that point, its not just the engine that gets put up to speed, but since its connected to the transmission, the trans is moved up to speed too. in other words, they are synchronized

3) u step on the clutch again to just put it into gear again (duhh).

its all to avoid massive clutch wear (or atleast more than normal) and keep ur trans healthy.
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Old 07-05-2004, 07:03 AM   #3
jcutsh
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Ok fellows,
Your almost there. The purpose of the double clutch is to spin the input shaft of the transmission.
Letís say your traveling at 50 mph in 5th gear and engine rpm is 2500. How many rpm would you need if you were traveling at 50 mph in 4th gear, letís say that engine rpm in 4th is 3500 rpm at 50 mph. Thatís 1000 rpm difference. So lets put the car into 4th from 5th at 50 mph.

1. Push the clutch.
2. Pull gear shift to neutral.
3. Push gas peddle till engine hits 3500 (we know itís 3500, because we know our car and thatís the rpm it runs at 50mph in 4th gear).
4. Pop the clutch (the clutch needs to move fast here about .10 seconds, about the time it takes to say the m in Mississippi, let the clutch out then right back in). This leaves the clutch disk and input shaft of the transmission spinning at 3500 rpm. Now we know that the tail shaft and gear assembly inside the tranny are all lined up at 3500 rpm at 50 mph. The syncro doesnít have any work to do because everything inside the transmission is all synced up. So...
5. Place the gear shift into 4th and release the clutch. Do not release the throttle from that 3500rpm point. You might throw yourself through the windshield. Unless your going for maxium effect release the throttle slowly or floor it to pass someone.

Letís say we want to shift to 3rd gear from 5th. Then we better know that we need to push the gas to 4700rpm, cause thatís the speed the engine turns at 50 mph in third.

If You donít release (Pop) the clutch in neutral and raise the rpm of the input shaft then nothing in the tranny is turning the same speed and the syncroís still have to do all the work for you. If your doing this constantly like on a track, the sycroís heat up and lose lubrication ability. This can cause the syncro to freeze to the gearset and your screwed.

Inygknok,
There is nothing in this procedure that will help or harm the clutch. All the clutch is doing is turning a 5 lb mass for that .10 sec. Thatís not much work compared to moving a 3000 lb car.

To be able to double clutch, you need to know what MPH and what RPM, for every single gear. All cars are different. Otherwise you wonít know what rpm to tap the engine to, in order to sync the gears.
Keep in mind, this is to help your transmission stay healthy. If itís to much for you then get an automatic or just drive normal. Driving can be hard work sometimes. If you are young, it will be fun. Once you learn it you wonít even think about it anymore. As you learn the speed of your car through the gears, use your ears. We use to play a game, we would use a blindfold, let a friend drive the car and try to guess speed, rpm, and gear with our ears only. Even by yourself you car close your eyes rev the engine and guess the rpm, (car not moving of course). Your car will constantly talk to you if you just listen.

There is another technique called clutch-less shifting which makes all this very apparent, but that is a whole other post.
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Old 07-05-2004, 07:28 AM   #4
VMJYogi
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OKay i figured it out (thanks to a helpful website) and i'll explain it to everyone in a clear manner. and to answer my own question no u cant and heres why....

the transmission is connected to the engine by what we know as a clutch there is a bar (we will use the word shaft) connected to the clutch's center. So when the clutch is pressed up against the flywheel (engaged) this shaft is spinning at the same speed as the engine. At the other end of the shaft is a gear which connects to another shaft (a layshaft) with 7 gears on it. (note. i am talking about a 5 speed transmission.) The layshaft gear closest to the engine is connected to the gear coming from the engine shaft. The next five gears connect to the 5 gears of your car which are located on the driveshaft. The final gear is connected to an idler gear which is connected to another gear on the driveshaft. This causes the final gear on the driveshaft to spin the opposite way thus creating reverse. Now all the gears connected to the driveshaft have bearings at their center so the driveshaft can spin at a different speed than the gears on it. Lastly there is a collar which is also connected to the driveshaft but has no bearings and always spins the same speed as the driveshaft. The collar is located in between each gear and is what u use to change gears. The collar has teeth on it which connect to the teeth on the driveshaft gears and then connects whichever gear you decide directly to the driveshaft. So that is how the tranny works. I dont expect anyone to understand this so i'll include a drawing.

! --<gear shift
_____________^______________
| | | | |
| | | | |
engine shaft | | | | | driveshaft
-----------------() (|)=={}=(|)={}=(|)={}=(|)={}=(|)=={}=(|)=====
()-----()-------()------()------()------()-------()
1 2 3 4 5 R
layshaft

legend: ---, shafts. (), gears. (|), gears with bearing. ===, driveshaft.
{}, collars.

So everything is connected at all times except the driveshaft. The object of double cluthing is to get the collars {} and gears (|) to be spinning at the same speed before putting it in gear. So u cant hold the clutch down because then the tranny wouldnt be getting input from the engine. u'd have no control over the rotation speed of the gears so the engine and gears need to be connected so u have the control. Thus u must engage the clutch (IN NEUTRAL) before clutching again and shifting gears. If there is anything i missed feel free to add it and umm thats all besides synchronizers but who the hell can draw that! Well...okay i'll try.

A synchronizer is something on each gear and collar used to get them to be spinning close to the same speed before the dog teeth attemp to engage. Heres a drawing. No need to really explain.
| ______
-|- - | >--->, >-->, >->, >>, >
/|\ |\ | engaging...............engaged
/ | \ | \ |
=| | |=====| | |======
\ | / | / |
\|/ |/ |
-|- -_____|
|
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Old 07-05-2004, 07:34 AM   #5
VMJYogi
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AWW GOD DAMMIT!!!! THE DRAWING DIDNT TURN OUT RIGHT. THATS IT PEOPLE IM RETIRED FROM THE WORLD OF AUTOS!!! :throws towel into garbage. punches screen. rubs hand. flicks screen off. gets looked at stupidly by sister for flcking off screen. closes door.:
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Old 07-07-2004, 06:56 PM   #6
Rocafella
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Duh!

You heard of preview post?
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