MTD lawn tractor speed control pulley stuck

Yes, I really should have moved the car before mowing that area of the lawn. Yesterday afternoon I managed to snag the clutch/brake control pedal of my 1996-vintage MTD garden tractor on the front bumper of an old station wagon wagon while mowing around the car. Before I knew what was happening, the pedal was bent backwards way too far and suddenly the tractor was locked into "high gear," and the speed control lever (still set for a moderate speed) wouldn't budge. I finished mowing the lawn by riding the clutch to control speed.
This is a belt-drive mower and I can see that the (6) speeds on this thing are selected via a split pulley that varies its effective diameter by the halves moving toward or away from each other. It appears to be locked in the furthest apart (smallest effective diameter) position, hence the "high gear" effect.
For the life of me I can't see how this variable pulley is controlled. There is a control rod that operates the "clutch" by moving the pulley assembly laterally and thereby loosening the drive belt. This is interlocked to the speed control lever with a Rube Goldberg-esque system of control rods, but the pulley halves don't move at all when the control rod is worked.
Anyone familiar with this setup? Ideas??
--
Roger Blake
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Not sure of the picture - but you might have to take the belt off to remove the pressure before you can slide the pulley back together.
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