Double-Clutching - Stupid Question Alert
 

OK... I'm going to show my stupidity and just ask this..

What is the big deal about double clutching - how is that somehow better or smoother than simply rev-matching before letting out the clutch?

I rev-match religiously; always blip the gas on a downshift before letting out the clutch once the the engine revs are where they need to be for a smooth shift, and be patient when upshifting, too. Even so, the clutch is never depressed for more than a second (and usually much less), and I'm not slamming from gear to gear.. let the momentum of the car work for you instead of fighting it.

Now, when double clutching, you're supposed to release the clutch with the shifter in neutral, THEN blip the gas to rev match, then press the clutch in, shift, and release the clutch? What does that gain you? It seems to me that, with that extra step, it's actually harder to quickly match revs.

And yes, I've driven hundreds of miles without a using the clutch at all... sometimes just 'cause it's fun, my left leg gets lazy, or it's just good practice in the unlikely event that the clutch goes. I've never lost a clutch in my life, but my clutch PEDAL would occasionally stop working on my first car (a Datsun B210.. yes, Tcoat, I'm at LEAST your vintage) so that's when I first learned a how to do w/out.

What happens mechanically when double-clutching that's better than what I've been doing for decades?

As always, I'm here to learn. Looking forward to being schooled.

Best to all..

Barry

You don't need to double clutch in modern cars because they have syncros. Just rev matching is all you need.

You can read a ELI5 here: http://auto.howstuffworks.com/manual...chronizers.htm

Double clutching is really only for non-synchro transmissions, like in older tractor trailers. If you are fast enough with the heal-toe action, double clutching is pointless.

https://en.wikipedia.org/wiki/Double...28technique%29

Just as the other two have said, no real need to with modern technology, but you'd certainly be bad ass if you were able to do it efficiently so you can show off your double-clutch heel-toe downshift's to your friends ;)

Yes, yes, understood... I know it's not necessary because, as you say, virtually all modern cars have synchros. My question is more, I guess, about what DIFFERENT happens in that intermediate step when you release the clutch in neutral.. how is that different mechanically then just leaving the clutch pressed in while shifting THROUGH neutral to the next gear while blipping the throttle to rev-match? Is not the clutch disengaged either way? Does something magic happen when you release the clutch with the tranny in neutral?

I may not understand fully how a clutch works and how synchros work, I guess. Sorry to be so dense. I understand the motions... just not the "why" part of things, I guess.

Can you elaborate further?

Thanks again..

Barry

[ame="https://www.youtube.com/watch?v=KXC2eoaw6Yw"]Fast and Furious - You never had me, You never Had your car - Granny Shifting Double Clutch - YouTube[/ame]

Lol, steve.. that cleared it up...

BTW, I did read the Wiki before even posting, and I also followed and read the link to the ELI5. I still don't see the difference as long as you rev match before releasing the clutch, whether or not you release the clutch in neutral first or not; that just seems like an extra step for no reason, w/ OR w/out synchros, assuming you've matched revs.

Does it have something to do w/ allowing the collar to return to a given position before negotiating to the next gear that ONLY happens if the shifter is in neutral and the clutch is released? Wouldn't the collar still move smoothly to it's desired locating as long as the revs are matched with the clutch depressed, thereby disengaging the tranny from engine anyway? If the revs are matched, heck, it'll slip smoothly into the right gear even WITHOUT the clutch being used at all.

Still foggy..

Barry

ill admit that even after 20yrs of driving, im still too chicken shit to learn how to shift without the clutch in any of my cars lol. i sorta tried once when i blew up the clutch on my integra on the track, but dammit i just couldnt get the hang of it. that was the most expensive towing bill ever :( hahah

in the words of @Tcoat

"Because racecar."

Gotta time it right lol

I learned to shift 2-4 on FRS w/o clutch but like you, too chicken to keep it up. Only thing I do now is blip throttle when downshifting.

When you rev match with the transmission in neutral and with your foot off the clutch, the input shaft is connected to the engine via the clutch and spins at the same speed as the engine. The output shaft is always spinning with the wheels. If engine speed is correct (rev matched) for the gear you are selecting, the synchros will do less work as the input shaft speed should be the same as the output shaft speed.

I downshift into 1st gear a lot. I find that without double clutching, the input shaft speed is too slow with respect to the output shaft speed so the synchro simply won't mesh (unable to match the speed of the input with the output shaft). In neutral with the clutch plate engaged I rev the engine to get the input shaft spinning faster and closer to the speed of the output shaft.

Don't give up on it; it's a good skill to have, and it really helps you drive better when you DO use the clutch, too. The car that really refined it for me was my first Fiat Spider. That thing would go into every gear SO smoothly when rev-matched that I really only used the clutch to start out in first gear. Find a car that's been around the block a few times and a little sloppy; it'll be easier to learn on, plus you won't care if you DO inadvertently make a few awful sounds. The secret, at least at first, is getting the engine revs a bit above where they'd be in your desired gear, then GENTLY holding the shifter against that gear as the revs drop and hit that sweet spot. If you miss it, or it doesn't slip in easily, don't force it... just try again. The first time it slips in smoothly, it's almost as good as... well....... the first time it slips in smoothly. You'll get it.

Barry

To the best of my knowledge there are two groups that double clutch modern trannys .
Those that have done it so long they think they need to.
And
Those that think the above clip is from a documentary.


On that note, I have never figured out if he means that you he was granny shifting and not double clutching for each shift or what. Since granny shifting is shifting up at low revs and double clutching is for down shifting then you don't ever do both at once anyway.

I'm not sure the physics behind double-clutching but damn does it help when the tranny is cold and I need to go to 2nd gear.

The syncros on my transmission did not hook up very well until they finally broke in. I went through a good 9000 miles religiously double-clutching my downshifts because spinning up the input shaft took way more effort than I was comfortable doing.

I'm at 18000 miles now and the syncros work beautifully. I hope they stay that way.

I still double-clutch into second if I miss my 1-2 shift when it's cold. And always into first if I'm moving at all. Just won't go otherwise.

I think there's some variation in the builds of this transmission because a friend's car will slip into first effortlessly up to 10 mph. Most other's are like mine - really picky with the lockout.