The brakes on my 96 olds Cierra are soft. The other day I found no brake fluid in the reservoir yet I can find no leaks. When the engine is off I have full pressure on the pedal. Once I start the engine I lose all pressure and I have only minimal back brakes.Would this be the master cylinder or the booster?
Neither. You have air in the lines, and your brakes are worn out and need replacement. ADDED: NEVER ADD BRAKE FLUID!! The brake master cylinder is designed to hold just the right amount of brake fluid for your brake system. There are two things to note. 1) As the brake pads wear out, the calipers piston has to move farther out to press on the brake pads. As the piston moves farther out, the area behind the piston becomes filled with more fluid from the master cylinder, and the level of fluid in the master cylinder goes down. When the fluid level in the master cylinder gets too low, a light should come on indicating that your brake fluid is low. That does NOT mean you need to add brake fluid. It means your brake pads are VERY close to being worn out. 2) If you add brake fluid today, and have your brakes done tomorrow, when the mechanic compresses the caliper piston ALL the excess brake fluid is going to spill out of the master cylinder all over the engine compartment and make a huge mess. Not to mention ruining your car. Just a note: Brake fluid does not evaporate. So, unless you have a leak, NEVER add brake fluid. Have your brakes serviced.
