What is Folo Thru drive? Construction and Operation.

Types Of Drive Arrangements

The drive arrangements may be of the two general types. It includes Bendix and Folo-Thru drive.

1. Inertia drive:

  • Bendix drive
  • Folo-Thru drive

2. Overrunning clutch drive.



The Folo-thru drive is almost very similar to the Bendix drive. The difference is that the Folo-thru drive keeps the starting motor engaged with the flywheel until the predetermined engine speed is reached, but in Bendix drive, it is not so. It works on a special locking arrangement to stay engaged with the flywheel.

In the Folo-thru drive, the threaded sleeve is attached to the armature shaft through a spiral spring. A pinion is mounted on the threaded sleeve. The pinion gear base has two small spring-loaded pins-an an anti-drift pin and a lock pin. The anti-drift pin is similar to the lock pin but has a stronger spring. 

Folo-thru drive
Folo-thru drive

The anti-drift pin rides on the anti-drift slope path on the threaded sleeve and it keeps the pinion from drifting into the ring gear up to when the starter is not in use. It imposes a fraction drag that holds the pinion gear in the disengaged position. The lock pin drops into a detent in the sleeve thread as the pinion moves out of the cranking position.

This holds the pinion from being disengaged with the flywheel during cranking. It prevents the pinion from being disengaged by a false start, during which the engine might fire a few times and then die. The pinion is thus held in an engaged position, and cranking continues until the engine really gets started.

Folo-thru drive
Folo-thru drive
Folo-Thru drive Detailed Internal Structure
Folo-Thru drive Detailed Internal Structure


When the engine has started and the engine speed increases, the centrifugal force on the lock pin causes to moves it out of detent; and the pinion disengaged from the flywheel. The over-running clutch prevents the starting motor from being damaged when the engine speed is greater than the starting motor speed.

In this condition, the pinion gear, still engaged by the lock pin, overruns the sleeve and ratchets over the clutch teeth. If the engine speed slows down, the pinion automatically resumes driving the flywheel as soon as the speed of the over-running parts decreases to the starting motor speed. This intermediate operation will continue until the engine speed increases to disengage the pinion from the flywheel.

Also, Read These Posts

  1. Car Starter or Starter Motor Problems.
  2. What is Over-Running Clutch Drive? Applications Of Over-Running Clutch.
  3. What is Bendix Drive? Construction and Operation.


Creative Blogger And Automobile Engineer.

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