Good find on the encoder.

I'm thinking there's no wipe in the down direction due to the weight being off, ie car wants to drift down. Since the car wants to drift down empty, it's always got pressure on one side of the teeth. If you run up, it's the same side. If you run down it's probably still wiping on the same side since gravity pulling the car down faster than the machines running the gears.

I bet if you lightened the car up or added weight to the counterweights so the car wanted to drift up empty, you'd see wipe on the opposite side of the teeth