ca993twin

Thaddeus,

I think you're kidding... but just to be clear, a slight pause (not speed-shifting) is generally sufficient to match the gear speeds on an upshift. This is well demonstrated by learning to shift without using a clutch at all... on someone else's car, of course.

Thaddeus

I was kidding, Steve; although I believe on VERY old cars it was also necessary to double-clutch on the upshift. I drove a Model T once where it was necessary. But maybe that was just an idiosyncrasy of an 85 year old transmission...

blau

What is the difference between double clutch and just merly matching revs.

Isn't the purpose of double clutching is to mach the higher revs when you down shift? So are they the same?

Also when you double clutch would you rather rev the engin higher or lower?

Also when you double clutch do you goose the engin to match rev then engage the clutch OR do you depress the gas match rev keep the gas stead while engaging the clutch.

sorry about all these dumb questions. But I want to drive this thing right. Maybe I should rent a car for the weekend to pratice.

blau

ca993twin

blau,

I'll repeat my previous post on double clutching:

"Its like "heel-n-toe" except that as you downshift, you pause in neutral, and let the clutch out, match the revs with the throttle, then clutch in and complete the downshift. It sounds harder and slower than it is... your feet are almost a blur, and the pause in neutral is momentary.

So what does it accomplish? Probably very little on a modern gearbox... but once again I'm an old geezer with some old habits. Double clutching will match the gears about to be selected to nearly exact revs, and the synchros are really not used at all. Thus... the synchros can last longer/almost forever. This is the technique to be used on gearboxes that had no synchromesh (hell... synchromesh is a fad and for wussies ). It still makes me feel good for the way it helps the gearbox last."

Rev matching without double clutching makes for smooth downshifts... nice and easy on the clutch and doesn't upset the chassis in spirited driving. But it does not match the revs INSIDE of the gearbox, and relies on the synchromesh to do the rev matching for the gears themslves. Synchromesh is subject to wear, although this seems to be less of an issue with modern transmissions.

Double clutching, on the other hand does not use or wear the synchromesh at all.

Lastly, a properly executed heel-n-toe double clutched downshift is a dying art form. It must be preserved... for our kids and our grandkids!

Aaron14

Before the 1920s, when there not syncros or angle cut gears, you had to double clutch to match the speeds of the input and output shafts in your transmission. Nowadays the only people that still double-clutch are semi-truck drivers, and older than dirt porsche owners!

Syncros were designed to keep you from having to double clutch, so don't feel bad about using them.

If you really want to double clutch it is not that difficult. Simply give the car a small amount of throttle as you depress the clutch and shift from whatever gear you are in to nuetral. Let the clutch all the way out, blip the throttle to a higher RPM than will be needed for your next gear (whether that be an upshift or downshift), and push in the clutch as the engine reaches the peak (highest) of RPM. Gently push the gear shifter into the desired gear, and as the RPMs of the gears within your transmission begin to match, you'll find the shifter slide easily into the desired gear. Now even if you do double clutch you will still put a very slight amount of wear on your syncros.

sidned

It tells me you know how to drive properly!

I'm in the same league as coltj - I blip the throttle once the clutch is depressed (which probably doesn't do the thrust/throw bearing much good) and release the clutch once it's in the lower gear. I can't practice on another car 'cause my wife drives an auto, but I'd love to learn how to do this properly.

orcfromthesouth

My understanding is that the 993 has double sinchros on 1 st and 2 nd. So I wouldn't worry too much. I also blip the throttle when downshifting if I'm pushing it so that the synchros don't get the full force. I also do it if upshifting under WOT. I never power shift, and have learned to take a nanosecond with my hand going from 1st to 2 nd and going to 3rd.

speed12sil

I do double clutching on both downshift and upshift and I'm not even 30. Hmm...

Now about that heel-toe double clutched downshift...Interesting

2ndof2

I usually give the car a blip of throttle before downshifting to match revs so I guess thats modern man's double-clutching (only kidding with my more "senior" and much more experienced P-car friends here!) . I have noticed that its sometimes difficult to easily get the car into first gear from a standstill at times and other times it goes into gear like butter. Particularly difficult when the car is rolling a bit which makes me cringe. I try not to ever force it. Second gear takes a bit of finesse at times also if I'm rolling slow and go from 1st to 2nd...almost like a pull straight back with the slightest bit of pull of the shifter to the right and it drops in nice and smoothly. At speed its no problem. Could this be a sign of synchro wear? I don't know but what I do know is that the idea of placing the car into 5th or 6th just prior to going to 1st gear for a roll-off from a dead stop seems to make that shift into first a little bit easier. Good tip to know. My only complaint about having to do that is impatient drivers behind me who hit the accelerator the second traffic lights turn green regardless if my stop lamps are still on! Already had one guy run right into the back of me in an suv and barely tapped me. His insurance had a $2700 repair bill and I was one bummed P-car owner for about a week. I had to drive my 928 that whole time --- horrible!!!!

ca993twin

I'm the sort of **** moron that watches for the yellow, and knows the stop light sequencing, so I can generally be prepared for the impending signal change. I know, however, that I truly am an **** moron, so I don't expect others to be bothering with this. I would expect most others to have better things to be doing with their lives.

993Dave

And yet we bow to your mastery of the Old Ways. I'm stuck with the blip-the-throttle-during-the-gear-change technique to save driveline lash, if nothing else. I thought that was pretty normal, but I when I attended a Skip Barber school a few years ago (just the paddock Driving School, not the race school), there were a lot of people who had no clue about heel-and-toe and matching revs. As fewer and fewer manual transmission are sold every year, the simple ability to use a clutch pedal will become a lost art.