May be a bad master cylinder, a bad sending unit from the master cylinder or the parking brake or the parking brake is not completely disengaging.
A symptom you almost always feel is a brake pedal that will not hold. You stop, hold the brake, and the pedal will slowly move toward the floor. This is a sure sign the master cylinder is bad. A leaking master cylinder or one that sticks, is also a sign is is defective. When you replace the master cylinder replace all the brake fluid in the brake system and bleed the brakes. Moisture in the brake fluid will destroy a master cylinder and this may be why it failed.Brake fluid leaking from the master cylinder. When you stop and hold your foot on the break the brake pedal will slowly go to the floor. Either of these symptoms means your master cylinder must be replaced.
You could have a leaking wheel brake cylinder. It could also be a bad brake line or a bad master cylinder.
Bad master cylinder.
Is a bad thing and requires IMMEDIATE REPLACEMENT OR REBUILDING OF THE MASTER CYLINDER TO PREVENT SERIOUS INJURY AND OR DEATH
No, it more commonly causes soft braking.
Air in a brake line or a bad master cylinder could cause this. Bleed the brake lines if you have been working on any brake cylinder. If this happened without any warning, the master brake cylinder is probably the cause and should be replaced.
Yes. The engine will idle poorly when a vacuum power brake booster goes bad. It can be a source of a large vacuum leak. A bad master cylinder however would have no effect on the performance of the engine.
First, make sure the master cylinder is filled with brake fluid. If it is low, there may be a leak somewhere in the brake lines or a brake cylinder. If the master cylinder is bad, you can normally pump the brakes up, but the pedal will slowly sink to the floor again. The master cylinder needs to be replaced or repaired.
If the master cylinder reservoir is empty, you have a leak somewhere. If the master cylinder reservoir is full, the master cylinder is bad.
Brake fluid is below the master cylinder sensor or the sensor itself is bad.
Normally this is caused by a Master Cylinder that has failed. Replace the Master Cylinder. Normally this is caused by the loss of fluid in the brake system. The fluid reservoir needs to be checked first. It possibly may be caused by a bad master cylinder but the most common cause is loss of brake fluid.