Hissing Brakes

CALEB129

MEMBER
JEEP CHEROKEE

I have a 1999 Jeep Grand Cherokee 4 wheel drive - 108,000 miles - 4.7 liters. There is a hissing sound coming from the floor pedals. When I accelerate, the hissing is less. When the pedals are not pressed, the hissing sound is constant. I noticed that when the accelerator is pressed and the hissing sound is less, the oil pressure is in the middle (at 3). While driving, and the hissing sound is lounder and more constant, the oil pressure drops to 1 or just below 1.
What could the problem be?

3 Replies

SERVICE WRITER

MECHANIC
9,123 POSTS

I suspect the hissing is a brake booster vacuum leak. If you can contort yourself to get your head down there and operate the accelerator and also the brake pedal with your hand t you may be able to distinguish the location. IT may be on the otherside of the firewall as well.

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Tuesday, August 21st, 2007 AT 7:30 AM

CHASS

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3 POSTS

Tess that sounds like what my 1990 Toyota 4funner. Is doing. I could hear that hissing sound for quite awhile before I replaced my master cylinder/booted combo. I bout from junk yard. Replaced as one unit. That hissing sound I
Been hearing for 2/3 months. Once I put the used parts on. I'm thinkn I still heard the hissn but barely. That was like 4 weeks ago. But today I had to jumped my Toyota I could hear the hissing it was alot louder. Could the jump make a problem some how! My hissing. Noise has always been there. Only issue I ever with my brakes.(Been driven my Toyota for 7 yrs). I was coming down a steep hill. And my brakes went out I thought cause it would not stop my foot peddle to floor. So I down shifted. But at bottom if the hill I had to run stop sign. I parked my car 3 blocks from there. I let it sit for 2/3 days. Tried to drive around block. Couple times. And u got my brakes back worked but nit as good. It's been 4 months and this. Was my problem the hissing brake booster. This whole time. When the hissn started. I kept telling them that my prob was the hissn shouldn't be there. My bro didn't relate that hissn to my brakes.

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Sunday, July 28th, 2013 AT 9:05 PM

CHASS

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So is the hissn noise. Or the air noise I hear now. I a vacuum leak or do u think that used booster. Already bad. My brakes were at 49 percent after I out in the used. Parts. Now they are at 1o percent.

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Sunday, July 28th, 2013 AT 9:14 PM