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If my understanding is correct, a car (in simple terms) has;

  • The crankshaft, then;
  • The clutch and gearbox, then;
  • The propshaft, then;
  • The differential, then;
  • The driveshafts and the wheels.

Therefore, assuming the car is in gear and the clutch pedal is not pressed, surely turning the crankshaft would turn the wheels, and move the car? If this is not the case, which component can spin without spinning the component it is connected to (other than the clutch)?

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  • Are you assuming that both wheels are in contact with the ground? And what about an lsd?
    – Solar Mike
    May 25, 2019 at 17:09
  • You are correct.
    – HandyHowie
    May 25, 2019 at 17:11
  • @SolarMike Yes, I would be assuming both wheels are in contact with the ground - would this make any difference, although I guess if only one wheel was raised and the other was on the ground, the differential would make a difference? Likewise, would the differential (or type of differential) make a significant difference, as surely the wheels would still rotate, albeit with one spinning faster/slower than the other?
    – PhysicsGuy123
    May 25, 2019 at 17:14
  • If one wheel can spin then the car may not move, which is why some have lsd...
    – Solar Mike
    May 25, 2019 at 17:16
  • Note, the layshaft is one of the shafts in the gearbox along with primary and third.
    – Solar Mike
    May 25, 2019 at 17:17

1 Answer 1

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You can put the transmission in neutral which will disconnect the engine/clutch/transmission input from transmission output/driveshaft/differential.

TO EDIT FOR YOUR CHANGED QUESTION:

Only in a standard transmission, but yes, it could be considered a direct drive. In an automatic there is a viscous coupling called a torque converter which sometimes is engaged, sometimes isn't. If, for some reason, the transmission is in gear and the clutch isn't slipping while engaged, and the vehicle isn't moving ... something is broke.

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  • I know that, I was just saying that if it is in gear, would there be any movement within the system, or would turning the crankshaft turn the wheels? Essentially, my question was whether a car in gear can be modelled as a "direct-drive" from the crankshaft to the wheels?
    – PhysicsGuy123
    May 25, 2019 at 16:56
  • The simple answer is yes, one could consider the configuration to be direct drive, only for a standard/manual transmission. I had a broken clutch in my teens. Putting the transmission in low gear, low range (4wd), I could hit the starter and the vehicle would move forward until it started. The starter turns the flywheel, which turns the crankshaft, which eventually turns the wheels.
    – fred_dot_u
    May 26, 2019 at 1:00

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