[Max Lobovsky]

There is another problem with sliding gears into each other that hasn't been mentioned here (well not exactly mentioned...). As said, it's a good way to strip your gears, but along with grinding the sides fo the gears as they engage, once they are partially engaged, All the force of the motor is being transferred via only part of the gear surface. You must have lower pitch gears than you might normally use in a non-shifting or dog-shifting transmission.