I had a failed wheel cylinder in my RR drum brake, replaced and brakes were functional, pedal normal. Noticed LR lost stopping power after a couple of weeks. It was a small wheel cylinder leak. I replaced that and decided to go ahead and install new shoes and hardware(springs, etc), bled system. No braking action at all. The reservoir was a little low, so I bench bled the master cylinder and reinstalled. There is still no braking action. The pedal esentially will not move, either with the engine on or off. I thought maybe the booster, but the plunger is going in and out of the master. I took off the FL tire, and there is no action in the front disc brakes as well. I have checked the equalizer in the master and have metal lines. There is a hissing under the hood when I press the brake. Could this be a vacuum problem, master failure, booster failure?
My car has 230000 miles.
My car has an automatic transmission.
If the brake system was working before and now the brake pedal is hard and the front calipers are not moving, then the brake booster has failed (which is the hissing sound that you are hearing) and there seems to be an issue with the calipers (possible dirty fluid). Check around the brake booster to see if the booster or the check valve is leaking. If the brake booster is leaking, I recommend replacing the booster. Then if the system still does not work, I recommend flushing the brake system. This will remove any deposits that could be in the fluid that would cause any blockages. If you need further assistance with your brake system, then seek out a professional, such as one from Your Mechanic, to help you.