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The brake servo or booster is divided into two chambers separated by a flexible diaphragm. Briefly there is vacuum on one side and pressing the brake pedal allows air to enter the other side and this is how the brake pedal effort is boosted.
The air enters via a filter through which the pushrod connected to the brake pedal passes. When the brake is applied the hiss of air entering the chamber will be audible; more on some models than others.
When the forces are balanced; when the brake is sufficiently applied no more air will be required and the hiss will cease. When the brakes are at rest; not applied there should be no hissing.
If there is it indicates a problem with the brake booster, perhaps dirt in the valve gear. Although repairs are possible they aren't very practical to carry out. A repair shop would probably charge more for fitting an overhaul kit than for replacing the unit.
If your car has power brakes, a slight hissing noise when depressing the brake pedal is not unusual. However, if you are having issues with the brake pedal felling stiff or hard, then you may have a vacuum leak in the power brake booster. If that is the case, it must be replaced.
yes but up to a point
the brake pedal should move about 1" to take up the pedal free play and then be applied smoothly as you press further
the harder you press the more solid stopping action you will get
that way you can feel the brakes working so that you can adjust the braking action for stopping
there should be no hissing noise that occurs when the brakes are being applied
you say hydro booster which is hydraulic booster but a hissing noise will come from an air leak in a vacuum brake booster which indicates that it needs repalcing
There are 2 things that can use vacuum near the brake pedal. If you have cruise control, there is a safety switch on the pedal to shut off the curise when you apply the brake. This switch may be leaking.
The other part is the brake booster, which is actually in the engine compartment but bolts to the firewall, and your brake pedal mechanism pushes into the booster. You will need to get your head under the dash with the engine running and press on the pedal to locate the leak--on the switch or on the wall.
your power brake booster is blown out
the seal has a leak in it
run the truck for 3 minutes and shut it off. with the windows up listen carefully while you gently apply the brakes
listen for a hissing sound of air leaking.
the sound of these leaking is a very soft sound
Sounds like a vacume leak from power break booster, when you loose vacume it will stall out the engine if enought vacume is lost. chk. power break booster. and hose from engine leading to booster for vacume leak, booster is under hood, break master cyl. bolts to it.
Thanks for the info!
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