Double Clutching

[champ]

I rented "Bullit "with Steve McQueen the other night.

Great flick . McQueen was a man for the ages .

During the famous car chase in which McQueen is driving the Mustang and he is switching gears it sounds like he is double clutching . Their was no smooth shift , more of a double sound .

I have no idea if that is what he is doing but I assumed that it was double clutching .

My questions to the gearheads out there are :

1) Was that double clutching ?

2) Why did he do this and what are the relative merits of this practice ?

FYI - McQueen was an accomplished race car driver and did all of the driving for that sequence.

 

[WhOiSyOdAdDy?]

http://www.felixwong.com/openroad/double_clutch.html

 

[Hung Wei Lo]

for #2, it's essentially a useless practice for up-shifting - it has something to do with synchro's and what not...i'd try explaining it, but it'd be like me trying to tell a George Carlin or Dennis Miller joke.. double-clutching is more usefull for downshifting (ie. to make the transition smoother from 3-2-1 and also helps with clutch wear) Heel and Toe is fun to try too!

 

[Dong Joe]

Double clutching is when you shift gears by going:

clutch in, stick to neutral, clutch out, clutch it, stick in gear, clutch out.

What the second, or 'double' application of the clutch does is aligns the gears so they mesh perfectly.

The only time I ever do this is when the car is stopped and I'm trying to get into reverse and it won't go. So into neutral, clutch out and in, ahhh there, that's better!

On some big rigs you HAVE to do this every time you downshift. However, my buddy can shift up through the first few gears without using the clutch at all! He does it by feel. He knows where the RPMs should be, sets it, and jams. This is faster and has less of the lag/jerk between shifts most big trucks exhibit.

 

[Cardinal Fang]

*Sigh of relief*

For a minute there I honestly thought this thread had something to do with a masturbation technique.

 

[jerbear]

Bullet to me is the best car chase movie I've seen , another good one was The Seven Ups with Roy Schrieder.

 

[parang]

ole dad

Basically double clutching is used with older vehicles when there was a lack of syncromesh gearboxes. Does not really serve any purpose with newer cars or trucks unless you are driving a transport.

 

[shack]

*Sigh of relief*

For a minute there I honestly thought this thread had something to do with a masturbation technique.

Good one. And I bet you were ready to try it out ASAP.

 

[aptenodytes]

Re: ole dad

Basically double clutching is used with older vehicles when there was a lack of syncromesh gearboxes. Does not really serve any purpose with newer cars or trucks unless you are driving a transport.

Even with synchros, double clutching can be useful, as it will extend the life of the synchros.
If you do a lot of 'sporty' driving and enjoy downshifting for the turns, etc., it sure won't hurt and can help.
Plus, it's fun.

 

[Why Not?]

Double clutching is when you shift gears by going:

clutch in, stick to neutral, clutch out, clutch it, stick in gear, clutch out.

What the second, or 'double' application of the clutch does is aligns the gears so they mesh perfectly.

DJ's explanation of how to double clutch is correct except that when double clutching on a down shift you also have to blip the throttle when the clutch is out and the transmission is in neutral.

The explanation of how it works is not quite right. Double clutching gets the 2 gears to be engaged spinning at approximately the same speed before engagement allowing them to mesh more easily. Modern transmissions accomplish this with synchronizers (cone clutches) which automatically do it.

Basically double clutching is used with older vehicles when there was a lack of syncromesh gearboxes. Does not really serve any purpose with newer cars or trucks unless you are driving a transport.

This is only partly true. When downshifting into a lower gear, at what is a relatively high speed for that gear, you should double clutch. This saves a great deal of wear and tear on the clutch and synchronizers. It is also a lot of fun to pull off a well executed downshift.

 

[Snake Pliskin]

It is also a lot of fun to pull off a well executed downshift.

IMO, heel & toe is required for a performance, racing style downshift. I race, and never double clutch, and don't know anyone who does. Everyone heel & toe's their downshifts.

 

[imhumorless]

Snake is right. Nowadays the idea when downshifting is to match the revs so that there is less transition between gears due to engine braking. The smoother the downshift A) the less dive there is in the suspension, B) the less drive line stress C) the less likely to momentarily slide the wheels if you are downshifting while cornering or braking at the limit. A stable car can enter the corner at hgiher speed. Its all about maintaining balance.

Even a race car with straight cut gears like a Jericho doesn't usually need to have the clutch let out when the car is in neutral (unless you are shifting too slowly), blipping the throttle the right amount will usually allow a smooth transition and less drive line lash (a good thing) when being driven at the limits of adhesion.

I don't know about open wheel cars with very little inertia in the drive train, but in big sports cars the amount of engine braking available when you screw up the downhift can be quite exciting, in a not good way.

Also big push rod V8 motors don't respond well to sudden increases in a no load (neutral) to high load situation. It places a lot of extra strain on the crankshaft and connecting rod bearings.

Smooth and gentle saves the car, and in order to finish first, first you have to finish!

 

[Why Not?]

IMO, heel & toe is required for a performance, racing style downshift. I race, and never double clutch, and don't know anyone who does. Everyone heel & toe's their downshifts.

Heel and toeing is having your right foot on both the brake and the gas and your left on the clutch working all three pedals at the same time. You can heel and toe and double clutch at the same time or do one or the other. They aren't mutually exclusive. If you want to see how coordinated you are try a heel-and-toe double-clutch downshift. I try it from time to time and it is a challenge.

I never suggested that double clutching was the appropiate method of shifting a race car in a race (a conventional double clutch downshift takes too long). As a matter of fact in real race cars with straight cut gears they don't even use the clutch to shift, they simply slip it into neutral as they are coming off the gas, blip the throttle and slip into the lower gear. Heel and toeing is not required for this as only 2 pedals are used. Lots of drivers in Nascar never "heel and toe". They use left foot braking, right foot on the gas and never touch the clutch except in the pits.

<edit> WRC and CART drivers routinely use left foot braking and no clutch as well. Not just the oval drivers. <edit>

In a street car, if you want the tranny to last the life of the car, double clutching on agressive downshifts is a good idea.

 

[imhumorless]

Just about 100% of stock car racing is done on ovals. They don't usually downshift at the limit. Road racers downshift when cornering sometimes. In my car the tranny (Jericho 4 speed) would usually need to be freshened up after about 16 hours if I use the clutch going up and down. This compares to about 10 to 12 hours if I don't use the clutch. And the guys at Jericho agreed with me. They did however say that the 5 speed isn't as fussy about the clutch versus no clutch question. They also said that the Jericho can be shifted without a clutch, as a matter of fact they like it that way- they get to sell more parts. Of course he was chuckling when he told me that. I would imagine the amount of power would have some bearing here too.

and for street cars, I agree with Why not. Heel and toe downshifts with a blip is a lot of fun, and reduces drive line shock too. Its a win win situation.

 

[Asterix]

Champ,

Bullitt is a great movie, one of my all time favorites; but McQueen didn't do most of the driving in that sequence, although it started out that way. The scene where he overshoots the curve and burns his tires backing up wasn't in the script. He really did lose control. The director/producers freaked, and not wanting to see their star wind up in the hospital, wisely replaced him with stunt drivers.

As far as the double clutching, I think they used it in the movie because they thought it sounded pretty cool, which it does.

 

[Meesh]

Heel and toe downshifts with a blip is a lot of fun, and reduces drive line shock too. Its a win win situation.

Does more than that too. Keeps the driveline shock from unbalancing the suspension entering a corner and helps prevent wheel lockup....making for a smoother, faster corner while taking care of the tires.

 

[clules]

I have a 3 door 1999 Saturn SC2 coupe, it's has a five speed gearbox and its the amazing thing to drive. Not a lot of power, just enough to make life fun without needing to fork out $60K plus on a "real" sportscar.

I have gotten into the habit of shifting down when I want to slow down or brake. I have got my gear change routine down pat. When I double clutch, it gives me the most amazing control over all aspects of slowing down the car. I do not have traction control or ABS. Even in the worst winter weather I have been able to stop on a dime. Eevn when other cars, with all the state-of-the-art gadgets, have gone into a skid.

I won't even go into the art of going around corners at speed.

I hope I never have to drive an automatic car again.

 

[Dong Joe]

Unless you have all-wheel-drive, downshifting will only slow the two wheels on the drivetrain, while braking slows all four.

When I have to slow down to a stop I go stick to neutral and hit the brakes. I learned at an advanced driving course that downshifting to a stop is not a good idea because brake pads are a lot cheaper to replace than transmissions.

 

[Meesh]

Proper downshifting is very little strain on the transmission.

Also, you should ALWAYS be in the proper gear to accelerate should an emergency arise. If you're in neutral one of your options for accident avoidance is gone.

IMHO, driving instructors should teach you how to DRIVE...not save on brake pads.

 

[Damondean]

The Double Clutch

I always thoight it meant clutching both boobs at the same time while performing DATY ..)