What's doubleclutching and how's it done?

Question

How badly will it mess up the clutch in the long run?

Answer 1

Gears rotating at different speeds cannot mesh easily. Double clutching is a way to synch-up gears rotating at different speeds so that the fast gear slows down (or the slow gear speeds up) so that they can mesh without grinding. It actually doesn't mess up gears if you employ it correctly. Rather, it prolongs their life. You're relying less on your synchros to synchronize your gears, and as such, you'll have less wear 'n tear on the transmission.

This technique is mostly used in large trucks or specialized cars (like race cars) these days. Most modern production cars don't need double-clutching. The reason why is because modern production cars use gear boxes that have "constant mesh" gears and "synchros" built into the transmission. In essence, the gears are always meshed, and instead of meshing/unmeshing gears with the stick, you're moving around a friction coupling to choose which gears to spin. The friction coupling matches the rotational speed before the dogteeth engage each other. It's a less efficient, and not as durable a gearing mechanism, but it's much more convenient to shift.

Trucks on the other hand benefit from having a heavy-duty and efficient transmission, so they often still have the more efficient "sequential manual gearbox" design that requires more skill from the driver: double-clutching. Not only is it a sturdier design, but you can build a SMG with many more gears than your standard six-gear manual transmission. Trucks need those extra gears to get to really high gear ratios to pull really heavy loads. Race cars also benefit from having a more efficient clutching mechanism simply for improved power transmission.

So, what is double clutching? Basically, you use one clutch motion to disengage the gear that you are initially using and get the transmission in neutral. At that point, you either speed up or slow down your engine rpm to match the intended gear that you're going to move into. If you're moving into a lower gear, you'll have to rev up the engine a little to match the lower gear, which is spinning faster than your initial gear. If you're moving into a higher gear, you'll have to let the engine rpm drop a little to match the higher gear, which should be spinning slower than the initial gear. Once you have the drive gear in approximately the same rotational speed as the next driven gear you're going to mesh into, you operate the clutch once more. This time, you operate it to get it from neutral into the next gear, and release the clutch once it's in gear. If you've done it right, the gears will be close enough in rotational speed such that you do not have any grinding. That...is how you double clutch.

Answer 2

Double clutching was used long ago to aid in the preventing of "grinding" the gears on manual transmissions. It does not hurt the gears or the clutch other than doubling the cycle on the throwout bearing. When changing gears, the clutch is depressed to shift to neutral. The clutch is released (with the transmission in neutral) and then depressed again quickly. The transmission is then put into whatever gear you want to use, and the clutch is again released. The release of the clutch in neutral slows or stops the gear rotation in the transmission, and makes the shift much smoother. Down shifting can be handled in the same way. Modern manual transmissions in small trucks and auto have syncronizers built into the transmissions that eliminate the need to do the "double clutching". Many of the large trucks now have many improvements that eliminate the need to do this.

Answer 3

As I understand it, in the early days of cars before transmissions had syncromesh mechanisms that align the gears as you shift (so they don't grind) people used to move the stick into neutral let the clutch out briefly before clutching again to engage the next gear. Usually they would rev the engine somewhat when in the neutral position this would supposedly get the tranny shafts spinning at or near the same speed so the gears would mesh more easily without grinding. Guys that drove big trucks used to do it all the time, but, it is not necessary with modern transmissions. It won't hurt the clutch at all, however it would be like using it twice as much if you did it all the time.

Answer 4

Double-clutching is when you use the clutch to take the
transmission out of gear then in a separate operation, use the
clutch to shift into the next gear. It isn't necessary in most
vehicles nowadays, just hold down the clutch for the entire shift.
Some semi-tractors (big trucks) still work well with double-clutch-
ing.

Answer 5

Double de-clutching was only necessary in old-fashioned cars.

The process is as follows. The clutch is applied and the car is taken out of gear. The foot is then taken up off the clutch and then re-applied, allowing a new gear to then be selected. Finally the clutch pedal is taken up again.

Modern manual-geared cars do not need to go through all this. A single application of the clutch is required to come out of one gear and select another. If double de-clutching is used, it will mean more clutch wear in the long run, but nowadays it is simply not necessary.

Answer 6

Constant Mesh Gearbox Working

Answer 7

you won't need to do it unless

A)It's a crappy car
B)Somethings wrong with your good car.

push in the clutch take out of gear into neutral
let go of clutch
push in the clutch again and put into gear
let go of clutch

Answer 8

doubleclutching refers to letting out the clutch momentarially while the gearshift is between gears, the object being to speed up the idle gear's in the transmision.
Modern car tranys. are syncromesh design meaning they have syncro's located just before the gear engagement dogs to do this for you