1998 caviler when brakes are applied engine revs up

May not be the booster as some do make a noise when the brakes are applied. To test press the brakes several times with engine off, Press the pedal down hard and start the engine , the pedal should move down slightly and there should be no whooshing sound . if the above is ok so is the booster.

Hard brake pedal when applied with the engine running. A quick test for the vacuum assist booster is to shut off engine, pump brake pedal 3 or 4 times and hold on the last pump, start engine and see if pedal drops a bit....if you detect a problem with booster you should check for adequate engine vacuum supply to booster when idling . You can sometime hear a hissing or air leaking when applying brake pedal with engine running if booster is defective

IT is probably a vacuum leak in the brake booster. With the pedal going to the floor There is either no brake fluid or you will have to bleed the system. Replace the booster and bleed the brakes starting at the longest line first

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

hissing noise is a leaking diaphram inside power brake booster.you have to replace the power brake booster.

This sounds like a bad vacuum leak, the brake system uses vacuum to power the brakes, if theres not enough vacuum to brake booster then the pedal will be hard to push and stop the car, open the hood and start and listen for a hissing sound, follow vacuum leaks and look for broken or aff vacuum lines. hope this helps.

Its very possible that you have internal vacuum leak in your power brake booster.Usually you'll hear a hissing noise while depressing the brake pedal,if that noise is evident then you have a faulty booster.

jcakey: My name is Roger and I will answer your question for you. From what you describe the problem sounds like a bad vacum brake booster. A simple way to check is to do the following. With the engine off. Press on the brake pedal 4 or 5 times. This will deplete all vacum in the booster. Next start the engine while holding your foot on the brake pedal. The pedal should drop a couple of inches. If the pedal does not drop. The problem is the brake booster. When the booster is bad you will hear a hissing sound inside of the truck when you apply the brakes..
If the master cylinder is faulty you will wave mushy brake to no brakes.Your ABS and brake failure lights will be on. Should you need further help please just ask. I will be glad to help you. Please rate this answer as this is how we know your answer was useful.Thank You for using Fix Ya. Roger

you have a vacuum leak from the brake booster probably down by the pedal if you can hear it inside the truck.

Hi,
From your description this appears to be a Brake servo issue.
The brakes are assisted by a vacuum created from the draw off the inlet manifold, it gives assistance too the brake pedal pressure by a large tank/cylinder mounted on the Bulkhead/firewall.
I feel that the sound you a hearing is air being draw into the Brake Servo from the foot pedal seal and the reason for fluctuation in the engine is the vacuum from the inlet manifold is being upset.
Attention I suspect should be addressed to the Brake servo/pedal seal or gaitor.
I hope this clarifies your thoughts?
Please remember to rate my effort.
Paul 'W'
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