Probably a dumb question BUT.....

In a big truck they have what is call a clutch brake When the clutch is depressed all the way, It locks the gears in the tranny, so to speak, this is why when double clutching you need to leave about 4" of the floor, personally, I float, no clutch at all, except for starting of in first

 

A clutch brake is what you say when sitting still. Running down the road shifting it's a matter of matching the engine's rotating speed with the transmission's/rear wheels rotating speed. That's why you clutch out, match speeds with the throttle, clutch in, engage.

Cars have what they call synchronizers in the transmission. It's a brass ring with nubs on it in front of each gear. It allows two gears spinning different speeds to mesh. Big trucks don't have synchronizers, so you double clutch to make the gears spin the same speed to mesh. When you hear all that grinding, that is someone trying to mesh two gears spinning different speeds.

Syncronizers are fragile and can break if someone doesn't know how to shift. That's one reason they don't use them in big trucks. There's trucks in Europe and Austrailia that use synchronizers.

To give you a better picture in general, the engines crankshaft extends into the transmission turning the front drive gear. The clutch is in the middle of that shaft allowing the shaft to seperate.

From the backside, you have the rear wheels and differential attached to the driveshaft extending into the back of the transmission turning the other gears.

There's plenty of websites that show you pictures of the inside a transmission or the whole drivetrain to better see how things work. Search out Eaton Fuller or Meritor to see some of the transmission websites.

 

It's a good question and one I asked during my tour at Truck Driving Boot Camp. The instructors stated that performing a double clutch is easier on the equipment. Everyone teaches it. Only the old timers still float the gears. When I trained I double clutched and my teacher floated the gears. The tractor was a new Freightliner and we both had trouble getting it into gear after switching drivers. Kinda made me laugh when the teacher couldn't get it into gear.

 

Nope, while I am fitting into the old class more and more, I'm by no means an old timer in trucking. I have more of a problem double-clutching, than floating. The school I just completed, did not teach or require you to double-clutch. The DMV examiner does not require double-clutching, here anyway. However each state, AND each examiner is different. IMO, both have some negative affects. Double-clutching tends to wear on the clutch more, and floating, if not able to do it proficiently will cause damage to the gears.

At the school I went to, they just replaced the transmission on one of the trucks. It was real tight, and the instructor also would have problems. It was real picky on the sweet spot.

 

Not a dumb question.

http://en.wikipedia.org/wiki/Double_clutch

Go to YouTube, search "double clutch."

 

WOW didnt know I was an "old timer" just thought I was experienced

 

When companies start paying statring quarterback wages, or even offensive lineman wages. Then I might think about wearing out my "clutch knee" instead of wearing out the company equipment.

Mikeeee

 

I would think most exsperienced drivers float the gears. Its so much easier. And as an O/O I say better on the equipment. Well as long as you do it right. You also need to know your equipment. Know what RPM matches what gear speed for the speed of the truck.