How does a TA work?

Can someone give me a laymans explaination of how a TA works? I'm trying to get it straight in my head exactly what is happening in the tramsmission when I engage the TA. Have two machines (884 and 706) with TA's, never had a problem with them but it's time I figure them out in case of problems.

They are a planetary gear set like the gears in your car's automatic transmission or an old Model T Ford.

A ta has 2 clutch packs that run by hydraullics 1 for directions drive which runs through the quill and a series of gears. The ta clutch pack runs through a differentiation
series of gears. The clutch packs are split through 3 seal rings on the shaft. When the ta side fails it falls back on the sprag which os the part hhat keeps your tractor from freewheeling. Kinda hard to explain without showing you in person.

The first style of TA used a planetary gear set with a ramp and roller over running clutch for the lower speed. They used a dry clutch, like the main clutch only smaller, to lock the complete assembly together to provide direct drive to the transmission. When in the TA position they will free wheel when going downhill.

The TA in your tractors use two pair of gears for different ratios with the upper gears on the input shaft and the lower gears on the speed transmission counter shaft. In the TA or lower speed position there is a one way sprag clutch that locks up between the front upper gear and the input shaft. It also has a hydraulic lockup that provides some lockup but is mainly there to keep the tractor from free wheeling. In the direct, higher speed, position there is a hydraulic lockup clutch to lock the rear gear to the input shaft. In this position the front gear will driven from the counter shaft and will be turning faster than the input shaft. The sprag will release to allow the gear to spin on the input shaft.

The TA works by giving you two different speeds on the speed transmission counter shaft. In the TA position the power comes in through the input shaft from the clutch and is transmitted to the lower shaft and then drives the rear upper gear in the TA at a speed less than then the input shaft speed. 4th gear is accomplished by engaging the 3/4 sliding gear on the upper speed transmission output shaft with the rear gear in the TA assembly. The other three speeds are achieved by engaging different upper shaft gears with mating gears on the counter shaft. In the Direct Drive position the power comes in the input shaft and the rear TA gear is locked to it. In 4th the power is just transmitted to the output shaft with no speed reduction in the speed transmission. The other three speeds have the power transmitted from the rear gear to the counter shaft and then back up through the selected gear set.

Does this mean that on a 460 the hydraulics have to be in place for the TA to work?

(quoted from post at 20:10:03 05/17/12) Does this mean that on a 460 the hydraulics have to be in place for the TA to work?

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No, a 460 uses a mechanical TA, no hydraulics are needed.