Why do truck drivers have to "double clutch?"?

My aunt and uncle truck, so I know I knew this; but couldn’t quite remember the reason just now, so I there’s a link. Of course, I remember now, but the link’s easier. (I also knew just how many gears there were, but all I remember now is that there are a lot, I don’t remember the number. I do know, though, that many of them are low gears that are normally able to be skipped over, and are there for pinches.)

I know one truck driver that never touches the clutch once he has his truck in motion. He will drop out of gear and wait for the engine sound to tell him to put it into the next gear without touching the clutch.

MThey have non-synchronized transmissions. Using a clutch while in motion is optional, you country float the gears, but either way is because the transmission is not synhronief. When you shift you have to match the engne speed and gear to the ground speed of the unit. It is not so simple at first, but once you get used to it you’d want it no other way.

How many forward gears do you believe are in a 500 horsepower Mack truck?

Double-clutching is mainly because their transmissions are so big, they are not synchronized, like manual drive sports cars.

Thier gear-shifting gives new meaning to “four in the floor”.

Thanks everyone. I was curious, since my husband is going to get a CDL. It was noted that the “old-school” way was to shift without a clutch, but double clutching was a requirement in passing the practical test now.

I do not always use the clutch in my car (usually do, though), but thought it was interesting that it was a requirement even if you could get away without it. I’m glad to understand it has to do with not having a synchronizer.

@Taciturnu If he doesn’t double-clutch for the road test, he WILL fail. The most important part of the test of the air brakes test. It is zero-tollerance fail that, fail all the test. The pre-test is a lot of memorization, and the skills test, though it varies from state to state, is a lot of practice. No truck driver on the road actually uses a clutch, they float, but it is required for the road test. Make sure he practices the pre-test, and remember the stuff inside the can as well, like the safety equiptment. If he decides to get a haz-mat, he will have to take that test everytime he renews. Tell him good luck, and to keep the bugs off his glass and the bears off his ass. ;-)

Thanks, @12Oaks. I’ll pass that on… :)

Are you a trucker?

@Taciturnu It’s part of my job.

I seem to remember older VW cars required double clutching…

My first car was the original VW Beetle, hot off the assembly line in 1957. I never had to double-clutch.

Non-synchronized transmissions need double-clutching This includes many trucks, and my old VW Golf (well, just between 2nd and 3rd).

According to the link provided by DancingMind: “Some large trucks on the other hand have so many gears that synchronizers are inefficient.”

I’m not sure, but I think one thing that synchronizers do is line up the teeth of one gear wheel to align with the spaces between the teeth of the one it’s going to mesh with.

I have never heard of this term, and by reading the link DancingMind provided, I realize that I double-clutch as a matter of daily driving, in my Honda. I thought everyone drove this way in stick-shift cars. It’s just intuitive; no one ever taught me. Do some people actually just gear-up and down with out going into neutral at all, ever except for stopping? Why would any manual driver NOT want to ‘double clutch’?

@Kraigmo You must be a “purist,” as mentioned in @DancingMind‘s link. :)
I occasionally shift without clutch completely, which is a swift move from one gear to another. It came in handy when I injured my left leg. I haven’t had a problem shifting from one gear into another without a pause in neutral, though. (When you clutch in, the car is essentially in neutral.) I was never taught double-clutching, but I imagine it’s more comfortable to drive as you learned. Since you learned double, it would be more comfortable to you than my single, and vice versa.

@Kraigmo More motion and slower shifts? In any transmission with working synchros, there is absolutely no benefit. For me, shifting is snappy, decisive, nearly instantaneous, and often rev-matched for added smoothness. My buddy often omits the clutch entirely.

Double-clutching on a consumer-grade vehicle (your basic car, pickup truck) is a waste of time.

Non-clutch shifting on a consumer-grade vehicle causes unnecessary wear and tear on the engine and transmission.

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Commercial transports (like tractor trailers) must operate in widely varying conditions under extremely different loads, and so there’s a greater need for these kinds of options, depending on what the current workload is.

@robmandu Things are slightly different when you drive an old beater that you don’t care about than a newer, more valuable vehicle that you do. They are also different when you have “dog gears” that are designed for no-clutch shifting, though those are usually not seen in normal cars, or at least not modern ones.

A truck driver double shifts because the shifter doesn’t always go into gear with one simple push of the clutch pedal. If you are a truck driver driving in the lower gears, you have to double clutch when you want to go in the higher gears. Hope this answers your question.