Once I start our 2000 Jeep GC Laredo there is a hissing sound (air/vacuum leak) down near the brake pedal. I have looked around but can't see any obvious point of origin. As I apply the break the sound increases/decreases but is always there. We drove a couple of miles and the sound stopped shortly after I applied the breaks and released but did it everytime I used the breaks. Any suggestions?
It it a brake booster problem.I am changing mine this weekend.You can get a new one form autozone for 149.00 or get one at the junkyard for about 70.00.I am installing mine this thanksgiving.I can send you the step by step instructions if you like.I have a 99 jeep grand cherokee limited edition and for once i thought i had a snake in the car..
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You have a vacuum leak, a bad one so it sounds. If the sound is a hissing sound, and it is coming from inside the car, by your feet, in the middle of the pedals, it is probably a brake booster leak. If the brakes are suddenly harder to use ie. you have to push real hard. the hissing is a good indicator that you have a vacuum leak. if the brakes are unaffected, its still most likely a vacuum leak. look around and find that leak.Once you find it (probably a hose). Plug it with something like screw (a long one that fits, is easier to find if you drop it). Then youll need to locate the other hose from which it broke. You may find a kit or something to repair it, but the best solution is to follow it to the other end and replace the whole hose. I just ignore my hissing, it is the brake booster, but ive gotten use to the extra pressure i have to use, and i know that a car thief would not know how to deal with my braking system...lol
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.
There are some solutions for this kind of problems: 1. change your brake fluid (BF). This need to done regularly every three yrs. , at hard condition's every two yrs. 2. check the caliper. It's possible that one of the two pistions inside the caliper don't work properly (mud or rust inside) 3. check if the brake bads can slip free over the anchor, if there are some rust on it, remove them and check the surface, if damaged, replace the part. 4. check the caliper slide pins. If the caliper can not slide, it will stay in contact with the brake disk, this will heat up the bad and disk and make a noise. 5. check your brake booster (vacuum test required). If you switch of the engine, listen if your hear some noises (air leak!). If all that wont work, come back again.
It maybe, I don`t know the vehicle personally but on Trucks and Buses, when this occurs, it usually points to the master cylinder piston seals which moves in and out as the foot pedal is operated. Does the hiss alter as the pedal is pushed down?? Does the hiss reduce or increase as the pedal is pushed down?? If it does, I think you`ll find that it`s this air seal between the piston and cylinder that`s failing and not the servo. Whether you car works the same way, I don`t know but I presume it must. Ian
There is a vacuum leak under the hood. On the 4.0 liter it is usually at the intake manifold near the brake booster. The 90 degree vacuum fitting pops off of the nipple of the intake. On the 5.2 liter the vacuum leak is usually near the battery where acid corrodes through the line as it passes near the battery box to the reservoir under the box.
has your brake pedal seem to be stiffer than usual? the sound you hear is from the brake booster if it has a leak it will cause a noise but you would have a stiffer pedal because the booster is loosing vacuum.