A stop on the gear? The motor does not have a stop, it will run continuously until it hits bottom, and continuously until it hits top. I don't believe it is possible to go past top unless you've disassembled more than the motor. I pulled the motors off my regulators and repacked the gearboxes, then reassembled. The motors brought the regulators back down with no issues.

I did this out of the car though, not sure if it matters.