What does it mean when normal brakes ''lock up'' and how do you get them to ''unlock''?

Answer 1

If by "normal brakes", you mean brakes without ABS (Antilock Brake System), then what it means is that the brakes have been pressed hard enough to stop the wheel rotating, so the tires skid and make that loud skidding noise and alot of smoke.

To unlock non-ABS brakes, you need to lessen the pressure on the brake pedal until the wheels start spinning again. This is called feathering the brakes. Non ABS brakes work the best when the wheel is spinning, and the brakes are applied to just before the point where the brakes lock up. This is one reason why driving a race car at the limit is such a skill, since race cars generally don't have ABS. The best race car drivers are those that can apply the brakes the hardest, i.e. just before they lock up.

Having said all that, the majoirty of passenger cars on the road have ABS. This is a system that does that brake feathering for you. So for most people, "normal" brakes do have ABS. You can tell when ABS is kicking in because the brake pedal pulsates under your foot, very noticeably.

ABS controlled brakes never really "lock up", since the ABS is designed to prevent that. The most important thing to do if you need to stop quickly and your ABS system kicks in is not to panic, and to keep the pressure on the brakes. Some people try to feather ABS brakes like they would old style brakes. This is very bad because the ABS system gets confused and doesn't know if you are really trying to stop wuickly or not. It is a good idea to go into an empty parking lot on a rainy day, get up to 25 mph and stomp on the brakes to see what it feels like so in an emergency, you are familiar with ABS.

The final type of lock up is a mechanical failure when calipers get stuck. This typically happens if you put the prak/emergency brake on and leave the car for a long time. The brake pads/calipers can lock in place, and you won't be able to move. This requires mechnical repair, although sometimes putting the car in neutral and rocking it back and forward can help.