The TA is the Torque Amplifier. Basiaclly a two-speed powershift. Your 656 has the Mechanical TA, which will not allow engine braking with the lever back. With the lever ahead, the planetary is "locked up" by the TA clutch and you get direct drive. With the lever back, power enters though the primary sun gear, travels through the planet gears, and leaves through the secondary sun gear, giving you a 33% gear reduction. While that is happening, the ring gear (around the outside of the planet gears) needs to be held still. A one-way clutch, commonly called the ramp and rollers, is used for this. This fine while the tractor is traveling on level ground or uphill, but when you go downhill, the ramp and rollers will overrun, and the tractor will freewheel. You must never travel downhill with the lever back, or you will damage the TA, or much worse, lose control and get yourself hurt. Get yourself a manual, learn how to keep the linkage ajusted, don't be afraid of wearing it out (use it!), and it will last.
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