Here's another argument against gear-minds. Start with the intuition that one cannot make a mind cease to exist without causally interacting with the individual whose mind it is or a part of the individual. Now imagine that the gears that the mind is made of are like those in this diagram . They have radiating spokes, and between the spokes is a hollow area. This reduces the weight of the gear while maintaining a significant portion of the strength.
Now, imagine that an inflexible spike is simultaneously inserted into the middle of every gap between spokes, without the spike touching any gear. Because the gears are no longer able to turn more than, say, a sixth of a rotation, and because any mental operation would surely require a larger turn of at least one wheel (we can stipulate this about our gear-person), a result of the introduction of the spikes is that the individual is no longer capable of any mental functioning. The gears can turn a little, but not enough to result in a mental operation. Moreover, no counterfactuals of the form "If input A were given, the individual would believe Q" are true any more. This means that if the functionalism requires such counterfactuals or the capability of mental functioning, as non-Aristotelian functionalisms are apt to require, there is no longer a mind. But because the spikes went between the spokes in such a way that no contact was made with any part of the individual, this violates the principle that one cannot make a mind cease to exist without causally interacting with the individual or a part thereof.