[katphishcatfish]

I never really knew about it or did it until I read about it here a while back and I was curious to know if any of you do it and how often/what gears.
For those who are like "What the hell is double clutching"-it's (and please correct me if I'm wrong) When you are down shifting from say 4th to 3rd, you tap the gas to get the RPMs in the range that they would normally be for a 4th to 3rd downshift. It supposedly saves on engine wear and tear. I've been doing it with the new whip and wanted to know if your guys utilize it.
Thanks

 

[nyibpass]

Re: Double Clutching (katphishcatfish)

That's what I call double-clutching, too. Used to be required on non-synchronized transmissions, AFAIK. I don't do it very often myself, but it can definitely save wear and stress on the linkages: the clutch and transmission itself. Taking double-clutching a step further, one can actually exactly match the revs needed for an up- or down-shift and slide the gearshift into gear without using the clutch. There's really no reason to do this unless you've had a clutch let go, because unless it's done very precisely and with authority, you'll either put a bit of extra wear on your synchro rings or just grind the gears. But knowing how saved me a tow on my old '79 Malibu wagon (3 speed on the floor).
I used to call this powershifting until i found out what that commonly refers to is upshifting w/o letting off the accelerator; ie, a good way to at least glaze a stock clutch on the Passat

 

[pass-variant]

Re: Double Clutching (nyibpass)

That's technically rev-matching... also called heel-and-toeing, if done while applying the brake).
Double Clutching, Using a 3rd to 2nd gear shift:
Push in clutch Layshaft equals Third gear speed
Select Neutral Layshaft coasts
Let out clutch Layshaft equals engine speed
Blip throttle Engine and layshaft speed up to Second gear speed and little
Push in clutch Layshaft coasts
Select Second No GRAUNCH if you have the speeds right. Ideally,
layshaft has coasted down to exactly Second gear speed
Let out clutch System is all locked up in Second.
It serves the exact same purpose, there's just more steps. The difference being that with the technique you mention, you still use the syncros when you do from 3 to 2, since the layshaft is still spinning at the 3rd gear speed or lower. You are matching the engine speed to the layshaft... the true double clutching matches the layshaft to the new gears (2 in this case) speed.
Make sense? It's worthless if you have working syncros. However if you didn't the above technique is what you would have to do in order to shift, whereas what you described would not allow you to shift.

 

[av_audi]

Re: Double Clutching (pass-variant)

Rev-matching, though recommended, is technically not part of the double clutching. Also, you don't need to let out the clutch completely when you are in neutral. I think just letting it off to the point of engagement (1/2 to 3/4) is enough.
I don't do it yet with my Passat as I sometimes did with my older car. For one thing, the clutch travel is way too long

and I just need some more time to get fully comfortable with the car. I don't even do heel and toe yet with my Passat.
But I just want to comment on "it's worthless if you have working syncros." That's not true. On some cars, when you shift too quickly, especially when you downshift, sometimes "working" synchros can't keep up and they grind. You are better off doing it then. In general though, it is useful in preventing premature wear of the syncros only if you are the type who does extremely quick and aggressive downshifts often. And I really mean very quick. For normal driving, it is indeed probably useless, but you have to start practicing somewhere

And it does take a lot of practice to get to the point where the double clutch action, ie. the twin pounding of the pedal on floor, sounds like two bullets fired from a machine gun

[Modified by av_audi, 3:19 PM 2-12-2002]

 

[bleslie]

Re: Double Clutching (pass-variant)

Let's talk about heel-and-toeing for a minute.
Is that just using the brake pedal with your heel and then blipping the throttle with your toe (both with the right foot) as you downshift to match revs? That's the only way I could imagine it.

 

[jelliotlevy]

Re: Double Clutching (bleslie)

I had to learn how to double clutch more than 30 years ago, when I owned a sh*tbucket '64 SAAB 96. The third gear synchro was totally shot, and one needed to do that when executing a 4 -3 downshift, using the handy column shift lever. Not of any particular value if you have a modern manual transmission in good shape. Double clutching is also handy if you have an archaic vehicle with non synchro first gear, and you want to shift into first before coming to a full stop.

 

[Becoolonce]

Re: Double Clutching (jelliotlevy)

The only "double clutching I have ever done is on the family 1946 (column shift)Willys Jeep which we still own to this VERY day. (This Jeep was one of the first 100 hundred ever sold for civilian use (comercial use) after War War II.)
As jelliotlevy said in the previous post, it is handy because there is no synchronization between 2nd gear and 1st. When it is desired to come to a stop, double clutching will get you into 1st gear from second gear before coming to a complete stop, otherwise the gears would clash and the force would be too strong to slip into 1st gear anyway.
Oh, and if you guys and gals ever want to feel brakes that take full pressure and weight to stop, try driving an old Willys Jeep. One has to almost stand on the brakes decending down a very steep hill. It feels like one is trying to stop a tractor loaded with a ton of weight in the back.
Oh, man....I can't wait for spring to get that old Jeep out!

[Modified by Becoolonce, 9:58 PM 2-12-2002]

 

[av_audi]

Re: Double Clutching (bleslie)

quote:[HR][/HR]Is that just using the brake pedal with your heel and then blipping the throttle with your toe (both with the right foot) as you downshift to match revs? That's the only way I could imagine it.[HR][/HR]​

Well, the usual way is braking with the ball of your foot, as you would normally do, then rotating your foot about the ball to blip the accelerator with your heel. Depending on the car, sometimes people just push the accelerator with the edge of their feet. If braking with your heel works for you, then why not, but it is harder to control braking pressure when braking like that.
The tricky part is being able to maintain steady pressure on the brake pedal while rotating your foot and pressing the accelerator. When you first practice, you might often loose braking pressure or jerk the car by increasing brake pressure. For that reason, it is a good idea to first practice on empty straight stretches of road. You don't want to inadvertantly let go of the brake while closing on a curve entrance

[Modified by av_audi, 12:42 PM 2-13-2002]

 

[av_audi]

Re: Double Clutching (Becoolonce)

quote:[HR][/HR]
Oh, and if you guys and gals ever want to feel brakes that take full pressure and weight to stop, try driving an old Willys Jeep. One has to almost stand on the brakes decending down a very steep hill. It feels like one is trying to stop a tractor loaded with a ton of weight in the back.[HR][/HR]​

I was reading some Formula 1 car specs a few years back, and I think the pedal pressure for maximum braking was listed at 120 lbs

and required maximum steering force was also tremendously high. I think they may have some braking and steering boost on today's F1 cars, but I am not sure.

 

[CooknFauVeh]

Re: Double Clutching (av_audi)

Av_Audi: power steering was just eliminated from Formula One.
Katphish: I always double clutch upshifting. I never did it until the emission controls started forcing manufacturers to hold a high idle during upshifts which makes the car lurch. Just push the clutch in, pull the gearshift back to neutral briefly, let out the clutch, push in back in, proceed to the next gear and let out the clutch. You will find your shifts to be much smoother, if less dramatic and quick.
A quick story on the effects of this technique:
I was taking lessons to get a CDL at one time, and the instructor asked me in amazement if I had driven a truck before, since I was double-clutching. I hadn't, but I don't think he believed me because my shifting was so smooth.

 

[Tox]

Re: Double Clutching (av_audi)

quote:[HR][/HR]...On some cars, when you shift too quickly, especially when you downshift, sometimes "working" synchros can't keep up and they grind. You are better off doing it then. In general though, it is useful in preventing premature wear of the syncros only if you are the type who does extremely quick and aggressive downshifts often. And I really mean very quick...[HR][/HR]​

I agree, except for one point. No matter how fast you learn to double-clutch on a downshift, IMO it will slow down your shift to the point that the synchros of a modern car could have kept up had you done a normal shift with equal quickness. In other words, while double-clutching really does work, the time it takes to do it renders it unnecessary. Catch-22.
I think I'm a pretty aggressive downshifter, but I haven't felt the need to double-clutch for 30 years (i.e., since I got rid of my '64 TR4).

 

[astacy]

Re: Double Clutching (Becoolonce)

quote:[HR][/HR]Oh, and if you guys and gals ever want to feel brakes that take full pressure and weight to stop, try driving an old Willys Jeep. One has to almost stand on the brakes decending down a very steep hill. It feels like one is trying to stop a tractor loaded with a ton of weight in the back.

Oh, man....I can't wait for spring to get that old Jeep out!
[HR][/HR]​

Yikes!!!

Remind me to stay at home on the days you put that beast on the road!! I'd hate to see you pull up behind me at a light.

 

[Becoolonce]

Re: Double Clutching (astacy)

Astacy........that cracked me up! You are safe from me.....I swear on it. The Jeep only stays on old dirt backroads that run near our farmland property in NH. Saftey First!

http://****************.com/smile/emthup.gif
The Jeep is used more like a farm tractor than a cruising mobile. That's why I bought a Passat!

[Modified by Becoolonce, 11:21 PM 2-14-2002]

 

[rcaton1]

Re: Double Clutching (katphishcatfish)

I swear that I've heard that term "double clutching" for the first time when Vin Diesel mumbled something about it on the Fast and the Furious. I got have someone teach me or at least demonstrate.