Double Clutching... Question

[Mike Feinstein]

I can't think of any viable reason to double clutch a modern (since mid-70's) car. Simply matching revs with heel-toe makes downshifts smooth and matches engine speed to transmission speed. Also saves your clutch and brakes. I do it every time...force of habit.

[jwetering]

I was going to say that double clutching saves the synchros....but you're absolutely right Mike - the wear and tear on the clutch pressure plate and hydraulics (if so equipped) kind of cancels out that benefit. Now, if your synchros are weak already, then it's another story.

cheers

[mperkins]

Eric Coffey wrote here:
Here's my (heel/toe) method:

#1. Apply brakes! (nail your braking point first).
#2. Clutch in.
#3. Downshift (no stopping off at neutral).
#4. Blip throttle.
#5. Clutch out.

#2-#5 is one fluid movement.

This is actually what i do as well,
I'm just having trouble incorporating the braking w/ the heel-toe part.

is this method smooth on the transmission and synchros??
and just seems that the traditional "double clutch" while in neutral is one step too many??

thoughts?

Maurice
'80 SC Coupe

[cab83_750]

HawgRyder,

I've been a senior member and was too embarassed to ask this never ending, numerous, repetitive double clutching.

Your simple explanation finally answered my questions.

Thanks!

[911pcars]

Hey guys,
jwetering was spot on with his 4 reasons for double-clutching. If you choose not to, then the synchro assemblies and/or clutch will wear faster. If you were to track downshifts, 2nd gear gets the most use, thus wears faster than the other synchros.

When you rev up the engine while in neutral and clutch engaged (pedal up), you are attempting to match the rotational speed of the gears on the input (engine side) and output (rear wheel) shafts so the synchro assembly doesn't have to "work" to accomplish the speed matching. This is 1/2 the double clutching procedure

Merely reving the engine while in neutral with the clutch disengaged (pedal down) only matches the engine (clutch) with the gearbox so clutch engagement is smooth - this is the other half of the procedure.

In practice, the double clutch is one continuous blip of the throttle as the clutch pedal goes down/up/down during the downshift. An extended double clutch (slow shift) will require two blips of the throttle.

Rebuilding the gearbox to replace the synchros, associated bearings and other pieces while you're there is more costly than R&R'ing a clutch assembly. Shouldn't that be reason enough? If you're a pro race driver, you may not care as much about synchro longevity.

Practice this method when you get a chance and you'll soon be doing this like M. Schumacher would (if he had a clutch pedal, that is). I'm pretty sure his paddle shifter system does the same thing using electronics/hydraulics.

Sherwood Lee
http://members.rennlist.org/911pcars

[Stanley]

While looking at the videos at bmwm5.com I found these videos on shifting techniques. Even though he explains it on a m5, the principals are all the same. The guy explains and demonstrates double clutching, heal and toe shifting, and launching.

For some reason if the link doesn't take you directly to the right site, just go to the directory "greg" on the main page, then to the shifting_videos


Link: ftp://www.bmwm5.com/bmwm5.com/movies/greg/shifting_videos/