the small white plastic gear set that is replaceable ( if the parts are still available ) are just for the odometer operation. the speedometer itself is run by a small electric motor that is controlled by the signal from the VSS. you do not have to pull the cluster from the dash to remove the speedometer. it pulls out towards the steering wheel when you get enough screws out (four if i remember right). it has to come straight towards you because of the electrical connections. the speedometer can be taken apart. parts of it are very delicate. when i took mine apart, the motor that controls the speedo needle fell apart in my hands. i found a used cluster and swapped parts until i had a working speedometer. you may want to go ahead and pull the cluster and closely inspect everything. the wiring, the connections, the circuit boards etc. if you haven't already done that. you can go ahead and upgrade your dash lights while you are there. i put in LED's. probably not worth taking apart just to do that - mine didn't improve all that much. the factory service manual has some good tips on trouble shooting the gauges and is good for helping to understand how it all works. if your odometer gears have never been replaced they are probably toast - the plastic on the original ones are not very good. make sure you shop around for those gears - some of the prices are outrageous!