Report: Cars are vulnerable to wireless hacking

[mahatmakanejeeves]

31. I had to think about this a while too. Here's what I came up with:

Before the advent of computer-controlled anti-lock brake systems (and that "computer-controlled" part is an important distinction), automotive brakes were pretty much all mechanical in their operation. When you stepped on the brake pedal, a piston in the brake system's master cylinder (in the engine compartment, directly in front of the driver) moved forward in the master cylinder. As it did, brake fluid was pressurized. The increase in pressure was transmitted through the brake lines to brake components at the individual wheels. If the wheels were slowed by drum brakes, the increased brake fluid pressure caused pistons in tiny wheel cylinders to move apart and press against brake shoes. If the wheels were slowed by disc brakes, the increased brake fluid pressure caused a piston to move within a cylinder in a brake caliper. Brake pads were squeezed against a brake rotor.

So far, it's all mechanical. There were mechanical anti-lock systems in the 70s. Some Lincoln Continentals of the era had anti-lock brakes, but the method by which the anti-lock feature came into play was a mechanical one involving weight transfer. I'll add more later.

ETA: I might be wrong on the method of actuation for the Lincoln. Wikipedia says that the '71 Imperial's system was computer-controlled. (I'll bet that was fun to work on.) The Continental's anti-lock brake system worked on the rear wheels only, which has me thinking that it was weight transfer that caused the feature to actuate. Wikipedia is not clear on that, but you can be sure that many car forums will be buzzing about this in the next few days.

Anti-lock braking system

Anti-lock systems that are computer controlled work differently. Speed sensors on each wheel note a difference in the wheels' rpm. If such a difference is detected during braking, the computer interprets a wheel that is rotating more slowly than another as one that is skidding. The computer overrides the brake pressure to the wheel that is rotating more slowly (or not at all) and reduces pressure in that wheel's brakes. When the errant wheel starts rotating at the same rate as the other wheels, the computer senses that its work is done. This cycle happens many times per second, as need be.

That's the problem. If you can persuade the computer that all the wheels are skidding, the computer will reduce brake pressure to all the wheels. They all keep turning, even though you are trying to stomp the brake pedal to the floor.

That's just my guess.