Aren't the brakes electric, too?

 

Brake assist is vacuum, I believe; it is on (virtually) all cars, and certainly is on the GE8 Fit. The ABS system is of course electrically powered.

Even without the power assist, there is still braking available; it just requires a lot more pressure on the pedal. This is true for any vehicle with hydraulic brakes. It's worthwhile to get a feel for this in a safe place such as an empty parking lot so you have some idea what to expect should you ever need to stop the car without power assist.

Those trucks and busses and similar vehicles that have air brakes are different. Without air pressure, the service brakes are inoperative and the parking brakes are applied full force automatically.

 

From what I've seen about air brakes, it the air pressure that releases the brakes. If there is no pressure, the brakes lock up.

 

Yes and no. The actual power to apply the brakes (i.e. to push the shoes or pads against the drum or disc) comes from air pressure, stored in an auxiliary reservoir. A clever triple valve controls the application of this air pressure to the brakes: if the supply pressure drops, it allows air to flow from the reservoir to the braking mechanism, and if it increases, it vents the pressure from the braking mechanism (to release the brakes) and also allows air to flow to refill the reservoir. So it's the air pressure that applies the brakes, but it's controlled by a drop in the air pressure in the system, and a sudden and complete loss of air pressure (say from a broken air hose) would indeed apply all the brakes with full force. If, however, the entire system is not pressurized, the service brakes cannot operate at all; pressing the brake pedal has no effect on them, unlike a hydraulic brake system where it still activates the brakes.

On a truck, there is also a parking/emergency brake system that is applied by spring pressure and released by the supply air pressure. This is separate from the service brakes (at least partly separate), rather akin to the hand brake on our Fits.

 

I watched an interesting series on Netflix, "Highway Thru Hell," about a towing company in NW Canada. They pull big rigs that flip over. Very often, the brake air lines are broken, and it's difficult to release each brake manually by turning a special bolt into each one.