I hear a hissing noise when brake pedal is depressed and slowly goes to floor and does not stop truck. But when I depess it fast it works as before. Master cylinder-no leaks. What do you think?
My car has 70000 miles.
My car has a manual transmission.
One of the most common causes of the brake pedal going to the floor is a loss of brake fluid. Generally, this is easy to detect due to the fact that there is usually brake fluid leaking on the ground underneath the vehicle. The brake booster is a mechanism that uses vacuum pressure to take the force being applied to the brake pedal and amplify it. If the booster is bad, then the full amount of force needed to activate the master cylinder and pressurize the brake fluid isn’t going to be there.
Another possible cause for this may be a failing master cylinder. The master cylinder is where the brake fluid is compressed creating the necessary hydraulic pressure the braking system needs in order for it to stop your vehicle. When the master cylinder fails, this may cause a loss of hydraulic pressure which will usually also cause the brake pedal to go to the floor. I would recommend having an expert from YourMechanic come to your location to diagnose your braking system.
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