Do I need to double clutch?

[Ronald F.]

I was reading about double clutching for the old-time vehicles. I've never done it with my 1967 L 71. Just wondering if it has a synchronized transmission or if I should be double clutching.

[Keith B.]

Re: Do I need to double clutch?

It's fully synchronized in all forward gears. Reverse is not. So before putting into reverse shift it into first gear. Then to reverse.

[Ronald F.]

Re: Do I need to double clutch?

Great info Keith! Thanks. Now it won't grind when going into reverse anymore.

[Bill H.]

Re: Do I need to double clutch?

I was reading about double clutching for the old-time vehicles. .

Old time vehicles = pre syncro.

But rev-matching your downshifts is kinder to your whole drivetrain.

[Wayne W.]

Re: Do I need to double clutch?

Synchronized transmissions have been around for a long time. My `31 Cadillac has a synhcronized transmission. The modern type synchronized transmission was invented in (`26-`27) by the brother of a Cadillac dealer in California, and shown to GM on a trip to Detroit in his modified cadillac. GM adopted the system shortly afterwards.

[Terry M.]

Re: Do I need to double clutch?

Synchronized transmissions have been around for a long time. My `31 Cadillac has a synhcronized transmission. The modern type synchronized transmission was invented in (`26-`27) by the brother of a Cadillac dealer in California, and shown to GM on a trip to Detroit in his modified cadillac. GM adopted the system shortly afterwards.

Wayne, is your Cadillac trans fully synchronized? My 1937 is synchronized in 2 & 3 only.

[Duke W.]

Re: Do I need to double clutch?

You don't need to double clutch with a sychromesh transmission, but you will certainly be a smoother driver and easier on the transmission and clutch if you do.

I read about heel-and-toe double clutch downshifting from Phil Hill in the pages of Road and Track in the early 1960s. It's a necessary technique if you want to be easy on the machinery and in the correct exit gear after slowing for a corner - either on a race track or on a twisty canyon road if you want to conquer them quickly and smoothly.

Before I got my SWC, I practiced the technique on every stick shift car that I was able to drive, and perfected the technique very quickly after I took delivery of my SWC in March, '63. I still use the technique, today, on all my cars, all of which have manual transmissions, but the degree of difficulty varies depending on the pedal layout.

When I tore down the T-10 for inspection at 115K miles the synchros looked near new and did not need to be replaced.

In the summer of '66 when I drove GM motor coaches in Alaska, I had no problem with the four-speed "crash boxes" (non-synchronized), which required double clutching both up and down. A professional motor coach driver who was on one of my sightseeing trips was amazed at my smoothness and mastery of the technique after only a couple of weeks of driving, so I told him the story of how I learned and perfected the techique in my Corvette.

The technique seems nearly lost, today, which is too bad. Very few people I know can drive a stick shift with any degree of alacrity.

Duke

[Bill H.]

Re: Do I need to double clutch?

You don't need to double clutch with a sychromesh transmission, but you will certainly be a smoother driver and easier on the transmission and clutch if you do.

I read about heel-and-toe double clutch downshifting from Phil Hill in the pages of Road and Track in the early 1960s. It's a necessary technique if you want to be easy on the machinery and in the correct exit gear after slowing for a corner - either on a race track or on a twisty canyon road if you want to conquer them quickly and smoothly.

Before I got my SWC, I practiced the technique on every stick shift car that I was able to drive, and perfected the technique very quickly after I took delivery of my SWC in March, '63. I still use the technique, today, on all my cars, all of which have manual transmissions, but the degree of difficulty varies depending on the pedal layout.


The technique seems nearly lost, today, which is too bad. Very few people I know can drive a stick shift with any degree of alacrity.

Duke

Yep, I've been using heel & toe on the street for a long time, usually don't realize I'm doing it.

Seems that I usually double clutch on the street and only rev match on the track.

I'm still teaching Corvette drivers how to heel & toe but about only 1 in 10 track day drivers are interested in learning it.

[Wayne W.]

Re: Do I need to double clutch?

Wayne, is your Cadillac trans fully synchronized? My 1937 is synchronized in 2 & 3 only.

Only 2-3 , with is common for three speeds.

[Michael W.]

Re: Do I need to double clutch?

Great info Keith! Thanks. Now it won't grind when going into reverse anymore.

If it grinds going into reverse, the clutch might not be releasing completely.

[Ronald F.]

Re: Do I need to double clutch?

I've been reading about Rev matching and heel toe shifting to learn more about it. Unfortunately it looks like my Corvette pedal layout is not ideal for practicing. By the way, isn't Revmatching only for downshifting?

[Bill H.]

Re: Do I need to double clutch?

I've been reading about Rev matching and heel toe shifting to learn more about it. Unfortunately it looks like my Corvette pedal layout is not ideal for practicing. By the way, isn't Revmatching only for downshifting?

Both double clutching and rev matching are only for downshifting.
What year, Ron?

While it's much easier to do with newer cars, it can be done on just about any car. The proper way is to put the ball of your foot (behind your big toe) on the right side of the brake pedal and blip the gas with the right side of your shoe (or heel if necessary) by rolling your knee towards the center of the car. The alternative way (sometimes necessary on cars with wide spaced pedals, like a vintage NASCAR) is to brake with your heel and blip the gas with your toes. Most race drivers will use the first method because you have more control of the brake pedal (for threshold braking) using your foot/ankle than when using your whole leg to apply the brakes. On the street, it probably doesn't matter that much.

Heel and toe is a great technique but, for the street, it's benefits are not as great as double clutching and rev matching. The main purpose of H & T is to keep the chassis set on corner entry. When you apply the brakes before entering a corner, the front end comes down and the front tires are loaded. Letting off the brakes to downshift decreases the load on the front tires (decreases the contact patch of the tire). Doing a heel & toe downshift maintains a constant load on the fronts making the turn in smoother, important when you're going fast.

For most street driving, letting off the brakes to downshift isn't a big deal. Double clutching is a bit easier on the syncros than rev matching but both and good for your drivetrain.

Heel & toe sure is fun though.

[Paul J.]

Re: Do I need to double clutch?

You only need a clutch to get going. It will slip into gear without the clutch with any syncronized transmission when revs match. This is an easy way to teach a young person how to drive a stick shift (after they get it moving). This works for both upshifting and for downshifting, and has nothing to do with the performance techniques discussed above, such as heel and toe.

[Ronald F.]

Re: Do I need to double clutch?

Bill, it's a 1967 convertible. It seems as if the brake pedal is much more forward positioned compared to the Accelerator and, To make things worse I have small feet. I'll probably have to practice on another car but I am anxious to learn more about this.

[Duke W.]

Re: Do I need to double clutch?

In order to rev-match you have to simultaneously manipulate both the brake and throttle pedals with your right foot as Bill explained above using the technique that best matches the pedal layout; and as he said, it's best if the pedal layout allows you to use the ball of your foot on the brake and roll your foot over to goose the throttle pedal. The ball of the foot is more sensitive than the heel, so it's best if the pedal layout allows this technique.

If you are braking at the limit of adhesion and just pull down a gear without rev-matching the resulting rev mismatch between the engine and driveshaft in the next lower gear can momentarily lock the rear, which can result in a spin. Rev-matching minimizes clutch wear, but does nothing to help the transmission synchronizers.

By letting out the clutch momentarily as you match revs, the transmission mainshaft speed is brought up to match driveshaft speed in the lower gear and the synchro has very little work to do.

We read many threads about downshift "grinding" especially when shifting down to second gear. The problem is worn out synchonizers due to lack of double clutching.

On a race track you usually need to downshift almost immediately after hitting the brakes to be in the proper exit gear at the corner apex, so mastery of the heel-and-toe technique IMO is mandatory if you want to be smooth and fast without beating up the clutch, transmission or risking a spin due to rear brake lockup. The guys who are spinning every other turn are the ham-fisted morons who just don't get it.

Do you want to be a truly expert driver - smooth, precise, and safe, whether on road or track? If so, then heel-and-toe double clutch downshifting is something you need to master.

I practice the technique in normal road driving because I've been doing it for over fifty years. Old habits die hard, and I'm in the right gear to instantly accelerate again regardless of speed - no fumbling with the clutch and shift lever when you need to GO!

Start by just practicing double clutch downshifting without braking. Once you have the double clutch technique down pat, add simultaneous braking, and practice, practice, practice! It's not easy to mater, especially if the pedal layout is poor, and most road cars are less than ideal.

Another example: The replacement (and known to be delicate) Borg-Warner T-50 five-speed in my Cosworth Vega has survived for over 70K miles including 5000 miles of race track hot-lapping. The original T-50 failed at 7K miles when first gear seized to the mainshaft, which was a common problem with the T-50 in the high-revving Cosworth.

I may have just gotten lucky that it didn't seize again, but shift action is as good today as the day it was installed, which I attribute to always double clutching the downshifts including use of the heel-an-toe techinque when simultaneous braking and downshifting was required.

BTW, the only vehicles I have ever owned that have/had near perfect pedal placement for heel-and-toe are my '91 MR2 and long gone '81 Diesel Rabbit both of which have small throttle pedals that pivot from above, and one of the worst layouts IMO are old Porsche 911s. Go figure!

Duke