The clutch pedal on a TA tractor works on two clutches. The master clutch (on the engine"s flywheel where you expect it), and a TA clutch. This clutch is 1/3 smaller but is similar in construction. It faces backwards and is mounted on the TA rotating parts. With the lever forward (direct) the following is a general description:
As the pedal is pushed down, the master clutch releases first(disengaged, no power through it). In about 3/4 of an inch or so farther, the TA clutch is released. From that point on down to the stop, both are not transmitting power.
If the TA is forward (direct drive to the trans) The TA clutch engages as the clutch is let up. This locks the TA reduction gears together, and causes the TA unit to spin in the direction of the engine rotation. As the clutch is released farther the master clutch engages, moving the tractor if it is in gear.
With the TA back (reduction), the TA clutch is held in released position by the linkage and its throwout bearing. The pedal will only operate the master clutch. When it is engaged (TA back) the TA input shaft rotates. Because the TA clutch is released, the gears operate. The reduction tries to spin the TA housing backwards while the gears try to turn the TAs output shaft forward. The TA housing is prevented from turning backward by a sprague (one way clutch) this allows the TA planetary gears to drive the TA output shaft forward, but in reduction.
Moving from reduction to direct: As the operator rapidly moves the lever forward (the only way to move it in or out of TA) the TA clutch is engaged, locking the gears together as a unit, and causing them to spin as a unit in the forward direction. The sprague clutch spins free in this direction.
Moving from direct to reduction, the TA clutch is released. The gears in the TA now are free and the housing stops spinning forward, and is restrained from turning backwards due to the sprague.
For the same reason we do not ride the clutch in a truck or car with a manual gear box, we do not slowly move the TA lever in and out of direct.
If the TA clutch is not completely disengaging when the ta in back, or when the clutch pedal is down all the way, the ta clutch will drag. This drag will prevent easy shifting of the trans when the tractor is on a hill going up forward, in forward gears, or going up a hill backing in reverse. This is because the tractor is hanging with pressure on the trans gears that are trying to turn the sprague the wrong way (which it will not do). This pressure on the teeth is what makes it had to shift out of gear.
A TA that is way out of adjustment can refuse to go into reduction, and will stay in direct (it might slip under load, but it is heating and will fail in that condition. A TA with a its clutch out will only have reduction and no Direct.
A TA with its sprague clutch out will have only direct, and when the TA is pulled back the TA unit will turn backwards and the tractor will appear to be in Neutral.
A failing TA sprague will sometimes work and other times not. Or it will fail under load stopping the tractor.
The tractor should be controlled so that at no time is the tractor moving faster in TA than it would in direct in that gear. The TA would then be over speeding and it is not good practice.
The tractor should free wheel in any gear in the direction of that gear with the TA back.
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