It depends on the vehicle type, but generally - when your brake pad thickness is 2 mm it is time to change the brake pad.
A brake pipe is an important part of a car. It is available in rolls of 25 foot long. Cars where the brake pipe is damaged are a danger in traffic. A good working brake pipe is important for the brakes.
The thickness of brake rotors are measured with a tool called a caliper. The specifications for the particular car will show the minimum thickness that a rotor can still be used.
It is important to have all the parts in a car in the best condition. The minimum front brake rotor thickness for this car is 21.4 millimeters or 0.843 inches.
The minimum brake rotor thickness for a 1994 Ford Thunderbird car is .974 inches for the front rotors and .657 inches for the rear rotors.
You need to get that vital info from a manual for that car.
Don't drive and take it straight to a garage 'cause it will empty your brake cylinder.
It could possibly be that your brake pads or brake shoes have worn down to the metal
When metal rubs against metal, it means the pad on your brake pad is wearing down. This can be extremely dangerous. If you notice any kind of unusual sounds, get your car checked immediately.
You can see this visually from outside the car. Check the thickness of the brake pads by looking through the outside of the wheel rims. If they're less than 1/4 inch thick, they need changing.
Year, Make and model need to be taken into consideration, 18 gauge is about the midpoint, some manufacturers / years may be thicker or thinner. The best way to match material size, is to use a metal thickness gauge on a known, good sample.
If the brake pads are not worn out check the backing plate. It is the thin metal plate behind the brake rotor, sometimes it will get bent and rub on the brake rotor.