I have a 2001 s80 and was told the hissing sound was the vacuum booster. replacment through dealer was expensive. so i called and found a place much much cheaper. How long do you think i can drive this car with leak before it goes completely out? i still need to get to work and make extra moey for repair, that may take up to 2 weeks

Check the large vacuum hose from the booster to the engine intake if the hose is good disconnect it at the booster and plug the hose if the hiss is gone the booster is bad if the hiss is still there remove the hose and plug vacuum nipple at the vacuum source if the hiss goes away replace the hose. I hope this helps. Take care.

Usually theres a plastic valve mounted on the booster thats connected to a vacuum source. Remove it from booster(they usually just pull out) & hose, then suck& blow on one end. Air should pass only one way. If it passes both ways the valve should be replaced. Check to c if hose holds vacuum by placing thumb on hose end to feel for suction (motor running) & to listen for hissing. Replace hose if suction is low &or hisses. Could be a vacuum leak elsewhere in wich case performance would suffer & idle would be eradical.

Call parts store for price of part. Replacement is not difficult so expect $100 to $150 labor.

The only problem with this system is that the dealer must calibrate the control module after repair is done, the cause of this may be due to a vacuum leak to booster or fault in brake pedal switch and last a bad booster. I would open the hood and try to see if you can hear a hissing noise or leaking line to brake booster.

you need a brake booster

It is the booster, but it might not be abnormal.

Vacuum from the engine is supplied to the booster, and vented if the brakes are not being applied.

When you step on the pedal, the movement of the pedal blocks the vents, allowing the vacuum to build up. That vacuum then pulls on a diaphragm, assisting you in applying the brakes.

Most people can’t hear that venting, some can.

You should, of course, have it checked out, but it sounds as if this might be normal operation.

The booster is bolted to the firewall, and then the brake master cylinder is bolted to the forward side of the booster.

To replace it you disconnect the brake pedal, remove the master cylinder, take the vacuum line off the booster, unbolt it from the firewall.

Install the new booster by reversing these steps.

But I don't think you need one, from what you say.

the brake booster sound like it hasahole in the diaphram, replace

Do you by any chance hear a hissing noise from under the dash? If so, yes, you have a bad booster. For it to do what you're saying, it would almost have to have a vacuum leak. However, if there is a problem with something in the ABS system, you should have an ABS warning light on. Also, ABS can make the pedal fade, but I've never heard of it making the pedal hard. Your diagnosis of a brake booster does sound likely, but I'll admit I can't be sure -- this is an odd one.

It appears the booster is bad.

IT SOUNDS LIKE A PROBLEM IN THE ACCUATOR MIGHT NEED ADJUSTMENT OR PROBLEM IN THAT CIRCUT