Press brakes, hissing sound, pedal hard and truck will not stop.
tgator2488 Member Posts: 1
edited August 2015 in GMC
recently, a car stopped suddenly if front of me and I hit the brakes very hard to stop. After that incident, when I press the brakes, a loud hissing noise is heard under the dash, the peddle goes down fast then gets very hard to press, while the truck almost will not stop. What is the problem, and how do you fix it.
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Any attempt to comment on what it is doing is far more likely to be wrong than right. A short hissing sound when you step on the brake pedal is actually normal since the brake booster would be allowing air to enter and help you push on the brake pedal. An extended or constant sound would NOT be normal, but that would be accompanied by a report that the pedal is as hard as a rock and not going down much at all.
When you state "the peddle goes down fast then gets very hard to press, while the truck almost will not stop" It suggests that you have a very low brake pedal and being this is a '96 my first suspicion is that maybe a brake line has failed. Is the fluid still full in the master cylinder reservoir or is the fluid very low?
If the fluid is low, you could add some and then have someone else pump the pedal while you look underneath the truck to see if you find any leaks. With the engine off, you could also apply and release the brake pedal and you will get an idea of what the system is doing without vacuum assist. Does the pedal still travel a long way, or does it become high and very firm?