Question

[DiehardDiesel]

  I am training in the diesel tech program at Abtech and I was reading the chapter in our book about clutches ,and one thing that confused me is on heavy duty clutches when the clutch is disengaged does the input shaft still spin.  I think so because we talked about that being the cause of grinding while shifting gears.  Also when coasting downhill with the clutch disengaged that causes the clutch disk to burst into pieces because the spining clutch housing causes the clutch to spin way over intended speeds because of driveline multiplication.  But my question is if the clutch is not pressed against the flywheel shouldnt it stop spining?



Diehard

[Snap-on Certifi]

there are two answers to your question.

First with the vehicle stopped the clutch pedal depressed and assuming that the out put shaft is stopped (vehicle not moving) and the transmission is in gear, no the input shaft is not moving. This does not hold true if the shifter is not in a gear(neutral). Due to the harmonics of the engine, the input shaft will tend to rotate. As the engine RPM is increased it will increase in speed as well, this is minimized with the lubricant being cold and the fluid thicker.

Second with the vehicle inmotion the input shaft is always in motion while the transmission is in gear. While the vehicle is in motion that means the output shaft is going and that is attached to the gear cluster and with the transmission is in gear; the input is turning. Two possible (but unlikely) ways that the input could be stopped while the vehicle is in motion. With the engine off or running and the clutch pedal is depressed and the transmission is in neutral. You still have to deal with the harmonics of the transmission gear cluster.

There were some applications many years ago that utilized an auxillary braking system to slow the input shaft speed while shifting; however they are extremely rare to see and I believe it is no longer a practise among manufacturers of any vehicle or equipment type.

I hope that clears up your question/s

[DiehardDiesel]

  Well almost I dont get why if the tranmission is out of gear with the clutch depressed why the input shaft would turn?   Also if the input shaft is turning most of the time that means that the clutch which is splined to the input shaft is also turning,  so when you depress the clutch pedal and engage the clutch it slows down a little but continues to spin correct?



John

[JoeR]

  Well almost I dont get why if the tranmission is out of gear with the clutch depressed why the input shaft would turn?   Also if the input shaft is turning most of the time that means that the clutch which is splined to the input shaft is also turning,  so when you depress the clutch pedal and engage the clutch it slows down a little but continues to spin correct?



John

The clutch can continue to spin even when disengaged because it is normal for there to be a little drag between the clutch and pressure plate (and flywheel).  If it was an ideal world, when you depressed the clutch pedal the clutch would stop spinning, but that's not always the case.
Joe