Double-Clutching?

[x635 4,066]

I've read some things online, but I hope someone can simplify this for me- what is "double clutching"? Is this still used in modern trucks?

I drive a manual transmission, how much harder is it to drive something with a double clutch?

[FiftyOnePride 100]

Matching RPM's to the speed of the gear you wish to shift into. It is necessary to do with our 13 as the transmission isn't synchronized.

Hope I explained that right, although I probably did not.

From my experience it has been hard for some, and easy for others. I think it depends on how often you drive a standard and confidence, speed of learning, etc.

Edited April 2, 2009 by FiftyOnePride

[antiquefirelt 994]

I'm no truck driver, so someone can correct or better my explanation. Double clutching is the act of depressing the clutch disengaging the gear to Neutral, letting the clutch out and then depressing it again and engaging the next gear. Basically you're double pumping the one clutch. Some throw in a quick goose of the throttle while the clutch is out and the transmission in neutral to keep the RPM's up, but I think that miht be truck specifc? The vollie FD I started with had all manual shifts and 4 of 5 of the apparatus required double clutching to properly synchronize the gears and shift. We upgraded to newer manual 6 speed Eaton trannys that were like shifting manual Honda Accord. Everything in my current job is an automatic with no reason to change.

[50-65 205]

Essentially it is a process to allow your engine RPM match your road speed. On the upshift, as you move the shifter through the neutral position, you release the clutch pedal, allow your RPM's to drop slightly to a range that will allow an easier transition into the next higher gear.

EX: At 2100 RPM you want to go into the next gear up. You press the clutch pedal, move the shifter into the neutral position at the same time releasing the clutch pedal. As the RPM's drop to about 1600 you push in the clutch pedal and move the shifter to the next gear.

On the down shift it is essentially the same except you have to give a little throttle as the shifter moves through the neutral position to keep the RPM's from dropping to low.

It's easier to show someone than to explain. And yes, on most heavy trucks it is still required to shift this way. With practice, and each truck is different, you may be able to time it so that you can shift without the clutch. However, if you miss the gear or don't have it all the way in gear, you can do some major damage to the transmission.

I have seen main gear shafts, about an 1" -1 1/2" hardened steel rod, bent from doing this.

Modern passenger cars and light trucks have a synchronized transmission which eliminates the need to double clutch.

With practice and experience, it really isn't any harder to do. It becomes second nature.

Hope that helps.

For real fun try an old Mack with a quadraplex tranny. Two shifters. One for the main transmission with 5 speeds and the second for the auxillary trans with 4 ranges. 20 speed trans but you have to shift both at the same time.

Edited April 2, 2009 by 50-65

[BFD1054 1,552]

Seth, good question. Everyone has had good replies and explained it pretty well.

I had no idea what the hell "double-clutching" was until i started working at my current job 5 1/2 years ago. One of our dump/plow trucks requires double-clutching (its a 1986 Mack). I was eager to learn how to drive it at first, but also quite hesitant. One of the guys taught me one day by putting around our lot unil i felt comfortable. Then, a few weeks later during a snow storm, i was assigned to the double-clutch Mack with an older guy. The older guy got tired of driving after awhile and was basically like "you're driving now" haha. It was the best thing for me. I just got in the driver seat and off i went with the little prior training i was given. It was a b***h at first i'll admit, but i got used to it. Now, whenever im called in for snow removal, i try and get to that truck 1st. Ill take it over the automatic any day!

But as antiquefirelt stated, its basically depressing the clutch, shifting to neutral, depressing the clutch again and shifting to your next gear, all while keeping your RPM's at a certain rate. It sounds harder and more in-depth than it really is. Downshifting however, is a whole other story. I still suck at downshifting, but like with anything else, practice makes perfect.

[PCFD ENG58 1,085]

Anyone what to bet that I can pull away from a dead stop with my 1968 Mack R685 Twin stick 237 turbo motor running in neutral no clutch PUT IT IN GEAR? You will lose, Its all in the ear. Gauges we don't need no stinking gauges!

[99subi 121]

Ya some of the older ones u can start off without using the clutch. hell some i drive today i dont use the clutch to shift

[firemoose827 324]

Anyone what to bet that I can pull away from a dead stop with my 1968 Mack R685 Twin stick 237 turbo motor running in neutral no clutch PUT IT IN GEAR? You will lose, Its all in the ear. Gauges we don't need no stinking gauges!

I was waiting for you to reply!

You have enough trucks and experience, you should start a driver school for fire trucks! I would be your first student to fail...I MEAN take the course! LOL

I cant drive double clutch to save my life, tried numerous drill nights and just could not down shift without having to come to a stop and start all over again...(Good thing we have the fair grounds to go and drive on at drill nights!)

[Deputy Chief Doug 0]

Anyone what to bet that I can pull away from a dead stop with my 1968 Mack R685 Twin stick 237 turbo motor running in neutral no clutch PUT IT IN GEAR? You will lose, Its all in the ear. Gauges we don't need no stinking gauges!

1/st low-low done that!!

[ckroll 101]

One needs to be able to shift synchronized standard as second nature before attempting to double clutch. Clutch, take it out of gear, release, match engine speed, then clutch and put it in the new gear. In much the same way, one can drive a standard car without using the clutch per se if one matches engine speeds. It's pretty easy going up with an older car, but downshifting is dicey as yes, one has to speed up the engine to match on the down shift. If one understands the physics of matching gear speeds and then listens to the engine, it's not hard at all. You do need to be one with your machine, and I think it makes for better drivers overall to have had the experience.

I fondly remember my fire department many years ago making it a rule that new drivers had to drive the 'original' a.k.a. double clutch trucks first in hopes of discouraging a certain woman who wanted to drive, unaware that she already knew how to double clutch a truck.

And double clutching also refers to taking the initial eggs of an endangered species to raise in captivity so that the parent birds will lay a second set of eggs to rear in the wild... double clutching..... but somehow, I don't think that was what he meant, is it?

[50-65 205]

Anyone what to bet that I can pull away from a dead stop with my 1968 Mack R685 Twin stick 237 turbo motor running in neutral no clutch PUT IT IN GEAR? You will lose, Its all in the ear. Gauges we don't need no stinking gauges!

yeah but with a 237 you ain't pulling away from much!!!!

[ny10570 745]

When you talk about making a truck sing, someone who knows their truck working the gears with just the throttle can really move and it is 100% by sound and feel when done right.

[firemoose827 324]

This has been a great thread guys, its helping me out a lot with learning how to better manage the double clutch. Out of our 3 engines, 2 are double clutch, our tanker is double clutch, the rest are automatics.

This brings up a question of mine to add to this discussion. Why is it that some departments feel its necessary to have these double clutch standards instead of purchasing automatics? Especially in a volunteer service, where 95% of the membership has possibly never even driven a standard vehicle let alone a large, double clutch engine or ladder, so why would they want to make it more difficult to get qualified drivers? You would think they would want to get automatics, this way training could be spent a majority of the time on Pump operations and water supply.

Thanks again for making this a good thread...what EMTBravo is all about.

[jack10562 414]

In order to make a gear change the two transmission gears have to be rotating at the same speed. Large truck manual transmission gears are typically too heavy to have synchronization rings. In transmissions that do have them, these gear-mounted rings rub together during the shift to bring the gears to the same speed so they can mesh cleanly for a gear change. Double clutching is done to release the load on the gears to be able to move the actuator and get the input and output gears turning at the same speed so they can mesh. On an up-shift, the input gear shaft is spinning faster than the output gear, so the input shaft from the engine has to slow down in order to move to the next speed. The opposite is true for a downshift, you have to rev the engine to get the input shaft spinning faster.