If you have a broken axle, what your car will do is nothing. That is, depending on the set up and which axle of course. Car axle's transfer power to the wheels, and can break due to; bad bearings, overloading, wear, or a rough bump. If you put your car in gear and hear a loud clunking and knocking noise, this is a good indicator. If upon acceleration the noise increases, most likely it's the axle. An worn axle will generally make a clicking noise before breaking (especially when turning).