I can measure?

Brake pads wear out as part of their normal operation. Rear brake pads only perform about 25 percent of the braking effort. As such, rear pads are smaller than front pads. With that in mind, you can expect to replace the rear brake pads once for every two to three times you replace the front pads.

Grinding means that metal is rubbing against metal. The shoes have worn down sufficiently to be digging into the interior of the drum. At worst, both shoes and drums will have to be replaced when this happens. At best, the shoes will need replacing and the drums will need resurfacing.

The brake pad wear indicator, which protrudes from the side of the pad and is set below the minimum thickness for the pad, rubs against the rotor and causes the squeal. If brakes make a grinding sound, they must be checked immediately.

The average brake pad replacement cost is $150 per axle, and can range from $100 per axle up to $300 per axle. There are a few other pieces of hardware that are found in the brake system which might need to be serviced as well, including calipers and rotors, but the most common service will be to replace brake pads.

Brake shoes today are still being used.  Drum brakes can provide more braking force than an equal diameter disc brake. Drum brakes last longer because drum brakes have increased friction contact area than a disc. Drum brakes are cheaper to manufacture than disc brakes.