Keep hearing a bunch of people talk about double-clutching for faster drag times. What is all this about? What is it, how do you do it, and does it really work?

 

From what I understand, Double clutching is basically 2 clutch depressions for every shift. You press the clutch to shift it out of gear, let it out while the car is in neutral (the time between when the gear you're leaving and the gear you're trying to get it into), and depress it again to shift it back into gear.

Although I don't know the actual drivetrain components involved, what double clutching does is it matches the rotational speed of the drivetrain components so you can get into the next gear smoother.

P.S. If any of this is incorrect please feel free to comment.

 

that's double clutching. Doesn't help in drag racing.

Speed shifting will help for drag racing but not recommended. (not using the clutch and cramming it into the next gear.)

 

Double (de)clutching is a process whereby the driver assumes the responsibilities of the synchronizers.

The order of events of normal shifting:

A) off gas
B) clutch in
C) pull back on shifter into neutral
D) synchronizer enguages and spins next gear shaft up to speed
E) dog teath enguage next gear
F) clutch out
G) gas on

The order of events in double (de)clutching:

A) off gas
B) clutch in
C) shift to neutral
D) clutch out
E) blip of gas to spin up tranny input shaft
G) clutch in
F) shift from neutral to selected gear
G) clutch out
H) gas on

An alternate series of events in double (de)clutching:

A) off gas
B) shift to neutral (no clutch)
C) blip gas
D) clutch in
E) shift to selected gear
F) clutch out
G) gas on

If you are really good with the gas pedal to engine RPM while transmission in neutral; you can use:

A) gas pedal to ~10%
B) shift to neutral
C) blip gas
D) slide into final gear
E) gas on

So, in effect, you (the driver) use the clutch twice and blip on the gas pedal (once) to perform the work that the synchronizers perform.

If you practice this a lot and get good at it, it is both fun, and just about as fast as normal clutch shifting (not power shifting). It works especially well in freezing weather when the transmission is still cold and the synchronizers not working properly (the synchs require the tranny oil to be at a particular viscocity to perform their work).

 

That is how you are taught to drive large apparatus with manual transmissions in the fire service. You drive with the rpm's.

 

Hanging on to the steering wheel very tightly with both hands?

 

It's something my father still does.He can't let it go.

 

Wow, lots of great info about shifting without using the clutch, especially when engine or tranny or both are under stress. Anyone know who makes Corvette clutch parts? I need to beef up my stock portfolio.

 

Double Clutching: verb What young guys do when first meeting an attractive young woman.

 

Only useful for down-shifting. Try going into a lower gear at speed, and then try the double clutch process as described above. You will find that it really smooths out the transition for the drive train by increasing the engine speed to match the effect of a gear change to a lower gear. It works very well. With practice you can come out of shorp turns much faster.

 

Shopdog just did an excellent treatise on this in partial response to my question, which was similar to yours. (this week) Though Mitch's writeup is pretty good too. Search and ye shall find.

 

Speedshifting BTW is leaving your foot (WOT) on the gas when you shift. You still use the clutch.

 

Should only be needed on non-synchronized heavy duty trucks, real old stuff. Most all modern stuff is fully syncronized.

If your trans has synchronizers and you have to double clutch it, they are wiped out. Letting the clutch out in nuetral spins up the gears, the synchros should be doing this job.

 

Double clutching is what used to be done way back in the 40's and 50's, when standards did not have syncros. If not at all, at least ones that worked very well. The double clutching affect allowed the transmission staft to catch up to input shaft speeds. Syncronizers do that today.

 

i thought speed shifting was shifting with the clutch without letting go of the gas.

 

If you speed shift without using the clutch, you'd better have a Lenco or Jerico - Something designed with racing straight cut gears.

Try that in a traditional trans and parts will shatter.

Nascar uses that type on road coarses, they just blip the throttle and grab the next gear without using the clutch. But that trans is getting rebuilt after the race. Yours needs to make it 100K + miles.

Most people just consider leaving the throttle floored and stabbing the clutch real fast and grabbing the next gear speed shifting.

Worked great in 60s muscle cars, especially with a Muncie rock crusher. Won't catch me doing it in a new Vette.

 

do you need to do double declutching in modern cars? I thought not, cuz of the syncronous mesh, i could be wrong, so i heard from someone..

 

There are a few instances where you *need* to double clutch. For example if you need to do a quick downshift from dawdling in 4th to 1st so you can get out of the way of an oncoming train or semi. If you just depend on the synchros in such a case, either the cone clutches will hold you out of the gear until they *finally* achieve a speed match, or if you yank the stick real hard you can override the cone clutches and the grinding sound you'll hear next is 10,000 miles of life being ground off the dog teeth. A quick double clutch will avoid that.

Just downshifting one gear at a time doesn't *need* double clutching, but it'll still save some wear on the cone clutches. With single downshifts, the more important thing is to just speed match, ie give the engine enough gas while passing through neutral so the car won't give a big lurch when you let out the clutch. In a track driving situation, where you're running at the edge of control anyway, failure to speed match can send you spinning off the track and into the weeds.

 

It is unnecessary in modern cars with synchros. I learned to do it because I'm an old geezer (53) and I had to learn to drive a 1949 dumptruck for my older brother.

It is fun to learn. Even modern vehicles will shift very smoothly if you double clutch. If you have a stick, learn both heel and toe (very useful) and how to double clutch. You'll know more than 99% of the drivers out there and be very easy on your clutch.

One more tip from Bragg-Smith drivers school. They cut their clutch failure rate to zero on when they instructed their driving students to avoid the throttle when starting from a full stop. Less revs=less heat=less chance to burn up the clutch. I'm not saying never use a little throttle, just nothing more than you really need.