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Can someone WHO KNOWS!!! please explane the proper way to double clutch.

 

And what does this accomplish anyway?

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Can someone WHO KNOWS!!! please explane the proper way to double clutch.

 

And what does this accomplish anyway?

I am not sure how it is done (there was an article on this exact topic in Autoweek some years ago), but it accomplishes the following: When you are downshifting, touble clutch trick allows you to match the RPMs of the motor to that of your transmission , so the downshift is accomplished smoother, without the lurch.

 

There was a lady rally-racer on this forum, she might explain it in more detail.

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Guest lothar34

Push in the clutch pedal, move the stick to neutral, release the clutch, revv the engine to the speed it needs to be going when you switch to whatever gear your switching to, push in the clutch, switch gears, release the clutch.

 

If you do it fast, you'll end up revving the engine with the clutch engaged, which is fine.

 

This saves wear on your synchros and shifts much smoother. If your car or truck has a whole lot of torque, shifting without matching revs can be a pretty big shock to the transmission.

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What lothar says is correct. As a tidbit of trivia, double clutching is good if the synchros are wearing. It stops the gears before the shift.

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can you suggest the best method for finding out what speed to match? I suppose just keeping an eye on speed and revs.

 

is there any advantage to doing this on my '00 OBS with 48K miles?

I just put in a short shifter too, which lets me switch a lot quicker, so the engine doesnt lose as many revs between.

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Well, helping synchros is only HALF the story, but it's good practice and develops your car control skills. Try braking with the ball of your foot at the same time as you downshift and roll you foot over to "blip" the throttle - whilst still braking!

 

The other half: Approaching a bend at racing speed, preferably on a track, you must also blip the throttle again before letting the clutch in, otherwise you will start a tail-slide because of the engine braking effect.

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Guest lothar34
can you suggest the best method for finding out what speed to match? I suppose just keeping an eye on speed and revs.

That's it. I really only do it if I'm downshifting coming off a freeway (and there's nobody tailing me). I started off watching, but now I can hear when the revs are right.

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Why would you want to 'double-clutch' a transmission that has syncronizers? In 35-years as a mechanic, I've never seen the center section of a syncro ring wear out. I have seen them break or tear the teeth off when someone was unsuccessful at double-clutching, but never wear out. Additionally, why put the additional wear & tear on the clutch linkage and clutch hydraulic system? I'd recommend using it like it was designed.

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Double clutching and rev matching are both good things in the right application, say, 56 Ford 4x4 and autocrossing. If you do them enough the motions with become ingrained and you will not think about it when you do it. Because I rally and autocross fairly frequently, I have gotten used to using both feet to brake and downshift and I try not upset the balance of the car. I unconsciously do it while driving everyday. Not perfect every time mind you, but I'm working on it.

 

I'm curious Phillip, How exactly was the clutch designed to be used?

 

Jay

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Good drivers always dd clutch changing down, poor drivers don't. It is a learned skill and requires practice, but after a while 2nd nature.

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When one does it properly and consistently, it gives better car control, and much less wear and stress on all the power train, save the clutch linkage and throwout bearing. My clutches typically last 200k miles plus - the clutch fingers that the throwout brearing contact typically wear out first.

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I'm not really a doubel clutcher but it sounds interesting.

 

Question is how does it help to let the clutch out in neutral then push it back in before downshifting? Why not just match the revs on the downshift but push the clutch in once, wouldn't that accomplish the same thing?

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Why double clutch when you can keep the clutch in and tap the throttle to bump up RPM's to match the speed of the lower gear? I have to agree with Phillip, that's why they make synchromesh trannies.

 

And why downshift coming off a freeway? I just use the brakes, then pop it outta gear without the clutch when my speed is low enough.

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Here is the proper way to double-clutch downshifting (this will answer everyone's questions): Let's say you're approaching a 30mph, 3rd gear, roughly 3000rpm corner at 40mph in 4th gear at roughly 2000rpm. Disengage the clutch and put the gearbox in Neutral. Re-engage the clutch. With your foot on the brake, pop the gas (heel-toe) and rev the engine up to about 3000rpm. Disengage the clutch, and immediately put the gearbox in 3rd. Since you just rev-matched it, the gear should engage smooth as silk, you shouldn't even feel resistance. Pop the gas again to bring the engine back up to about 3000rpm again and then re-engage the clutch, it should be instantaneous and without jerking. You have just put the car in the proper gear and at the proper rpm for the turn without doing any damage to your transmission. A practiced driver can do this entire process in a half-second.

 

But hold on, before you all start popping clutches 50,000 times a minute, understand that this puts an extra strain on your clutch release system. I still stand by my notion that the throwout bearing clips broke off the clutch fork on my Legacy because I learned to double-clutch on that car.

 

And I can drive MT with the best in the world. Guys who have been driving MT for 30 years ask me how I drive so well, I just tell them I'm self-taught :).

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My 94 legacy is grinding going into second especially when downshifting, so I am in the process of learning the whole double clutching thing. Now just to get my wife to learn...:rolleyes:

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DRACO!

 

 

The first stage is intended to bring the gearbox internals up to speed, that's why the clutch pedal has to come up, otherwise you are just revving the engine.

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Double clutching on cars is only to help reduce wear on the tranny, which with synchros isn't a big issue to start with. I think that taking the extra time that double clutching takes could be used to shift the lever slower, and give the synchros more time to speed match and that would do the same thing. Coming into corners, you can just RPM match the engine to the speed and gear with the clutch out to get the jerk free engagement. The only place where double clutching is neccesary is on big trucks, where the combonation of the lack of synchros (on the older trucks) and the inertia of the gears in the tranny is such that you have to use the engine to match the gears or they will tear themselves apart. Good drivers neutral throttle the engine, shift into neutral and then match the engine speed (and with it half the tranny speed) to the gear they're about to shift into, then just slide the lever into the next gear. this is the minimum wear way to shift. My neighbor can do it with his trash trucks, he only uses the clutch to take off, for every other gear he just no-clutches it. No grinding, no working the clutch, just as smooth as can be.

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Hmm, I find that clutchless shifting is VERY hard to get right in an AWD car. No problem in many 2WD's, but the weak Sube synchro and the extra inertia of AWD make it a very crunchy affair. Best avoided.

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I’m with 91Loyale on this one.

 

Double clutching is completely unnecessary with a full synchromesh trans in good working order, the transmission itself has all the necessary parts to match the shaft speeds… they are called Synchronizers! (Sorry to be a smartass). The synhrcos have a cone area that leads the teeth and starts to wedge with the gear, this matches the shaft speeds before the synchro teeth engage. If reduced wear is your aim just shift a bit slower, this will give the synchros time to do there job more completely and still be faster than double clutching, and without the extra wear on the clutch (which is far more likely to wear out than a gearbox). If you doubt this conclusion then consider this... when you make a normal shift, without double clutching or RPM matching, when does the lurch occur? When you let out the clutch, right? Not when you shift. At this point the gears are already meshed, it’s the inertia of the engine and flywheel that you feel, and this can be lessened by simple RPM matching before the clutch is engaged.

 

Now, can double clutching help reduce grinding or hard shifting, Yes. But his is only compensation for worn or abused parts. In this case double clutching can postpone the eventual trans rebuild.

Double clutching and clutchless shifting can be fun to perfect and are neat tricks to impress the girls, but good stick technique and RPM matching are all you need to be smooth and quick without grenading the transmission.

Gary

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You dd clutch changing down to speed up the internals and then the syncro's have less to do. It's simply laziness not to do it. BUT it does take considerable practice to do it correctly and I know a few will never get it. My wife has been driving for over 20 yrs but gave up in disgust and just in time too as our relationship became 'strained'. Talk to any transmission shop worth their salt and they will be able to explain the benefits, but it will take possibly business away from them so not all will provide honest answers. Using a good gear oil helps too (and I'm not talking about the Sube OEM dino).

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