You have brake problems on a cadillac deville and i think its the master cylinder?

It's possible that the master cylinder is the cause of your brake problems, but there are several other components that could also be causing the issue. Here are some of the most common brake problems and their possible causes:

1. Brake pedal feels spongy or soft: This can be caused by air in the brake lines, low brake fluid, or a faulty master cylinder.

2. Brake pedal goes all the way to the floor: This can be caused by a faulty master cylinder, a broken brake line, or a problem with the brake booster.

3. Brakes feel like they're grabbing or locking up: This can be caused by a faulty ABS module, a problem with the brake calipers or rotors, or a problem with the brake fluid.

4. Brakes make a grinding or squealing noise: This can be caused by worn brake pads, a dirty or damaged rotor, or a problem with the brake caliper.

5. Brakes don't work at all: This can be caused by a faulty master cylinder, a broken brake line, or a problem with the brake booster.

If you're experiencing any of these brake problems, it's important to have your car inspected by a qualified mechanic as soon as possible. Driving with faulty brakes can be dangerous and could lead to an accident.