I've had the situation that Joe speaks of. On the wifes 36 chevy with the original hydraulic brake lines/system, one of the rubber lines had a piece of internal part of the hose come free creating a "flap". Fluid would easily go out to the brakes but wouldn't return quickly. When this happened, the car severly pulled to the right (or where ever the bad hose was), and nearly pulled you off the road. It didn't cause DW but just a strong pull that caused the steering wheel to jerk so bad it nearly pull it out of your hands. Needless to say... we hunted that problem down so it wouldn't show up again.
Jerome