Yes, GEARS is a Scrabble word!

Letter values in Scrabble US: G 2, E 1, A 1, R 1, S 1.

Is it a valid word?

GEARS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a toothed wheel that engages another toothed mechanism in order to change the speed or direction of transmitted motion
wheelwork consisting of a connected set of rotating gears by which force is transmitted or motion or torque is changed
a mechanism for transmitting motion for some specific purpose (as the steering gear of a vehicle)
equipment consisting of miscellaneous articles needed for a particular operation or sport etc.

Also: gear wheel, geared wheel, power train, gear mechanism.

Not playable in Scrabble US: GEARTRAIN.