It's beautiful outside (Massachusetts) and I finally got the chance to roll down the windows. I noticed that when I step on the brake while in the driveway I hear a PSSSFFT sound coming from the engine area (driver side) ... similar to letting air out of the tire for about half a second or so. This is on our white S70.

Last November 2005, the dealer replaced the brake master cylinder because of a slow leak (see my previous post http://www.brickboard.com/AWD/index.htm?id=1019919) and the brake pedal was going low. Everything seems to work fine up to now with the brakes except for the sound. I tried the brakes on our other (red) S70 and there was no sound.

What is happening?

Thank in advance.


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Brian M. - 1998 S70GLT, 1998 S70 GTA

I had the same hissing sound from my S80. The dealer told me that they replaced the brake booster and a power cylinder. Total cost with labor was $755.00us, covered under my extended warranty. Hope this helps.

I hope it's not the brake booster. The dealer bled the brakes back in April 2005. When the brake pedal started to run low again in November 2005 because of a slow leak, they replaced the master cylinder. It seemed to have solved the leak but the brake feel didn't inspire confidence compared to that of our other S70. And now this hissing sound.

What are the chances of the master cylinder and brake booster failing within a span of 4 months?
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Brian M. - 1998 S70GLT, 1998 S70 GTA

The brakes have a servo motor under the driver's side windshield under the hood. From there, extends a vacuum hose that is routed around to under the air filter box and then to under the air intake hose to the front of the throttle body area. I would suspect that this hose has a leak in it. Check it and replace if necessary. Not sure exactly what the servo motor and vacuum hose do, and seems unrelated to actual operation of the brakes, though I do think it is used to slow the engine when you are actually braking.
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1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon. My cars have been running so well lately they've got me worried.

Hi, just an update.

I brought it the dealer and had a Volvo tech listen to the hissing noise. He said he wasn't sure if the sound was normal or not. What he said was that the rear pads needs replacing soon and also might be sticking. He suggested the system needs to be bled after inspecting the brakes and/or replacing the rear pads.

I will be setting up an appointment with the service department in a couple of weeks.

P.S. They bled the brake system last April 2005 and then replaced the master cylinder last November 2005 when the pedal was going low again.
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Brian M. - 1998 S70GLT, 1998 S70 GTA

I sure am glad I don't have to go to your dealer! You need new rear pads and brake fluid needs to be bled? He could tell because he heard a hissing noise when he stepped on the brake?
You don't need to bleed the brakes when changing pads. There is no reason to bleed the brakes unless you have had one of the brake lines open, like when getting new calipers.
Can you get someone else to step on the brakes while you open the engine bay and listen? It has to be a vacuum leak.

Klaus
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(V♂LV♂s 1975 164, 1995 854T, 1998 V70R)

Oops. Let me correct myself. The tech confirmed that the hissing sound was there but wasn't sure what was causing it.

I forgot to mention that the dealer bled the brakes back in April 2005. When the brake pedal started to run low again in November 2005 because of a slow leak, they replaced the master cylinder. It seemed to have solved the leak but the brake feel didn't inspire confidence compared to that of our other S70. Also, the hissing sound occurs when I stomp on the brake pedal with the car in park. This hiss sound is not consistent in length .. varies from a split second to a second and sometimes it's not there.

Now someone mentioned the brake booster. I hope not! What are the symptoms of a failing booster anyway?
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Brian M. - 1998 S70GLT, 1998 S70 GTA

To test the booster: with the car turned off, push on the brake pedal as hard as you can and keep the pressure on, then start the car. If the pedal starts to sink after the car starts, the booster is working normally.
I have to agree with MIJ. You have a leak in that hose, just replace it. It is a cheap and easy fix.

Klaus
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(V♂LV♂s 1975 164, 1995 854T, 1998 V70R)

I actually had the hood up while the tech listened as I stomped on the brake. The tech wasn't sure if the hissing sound. He then visually checked the front and rear pads and found the rears need replacing. Since he wasn't exactly sure what the sound was he wanted to bleed the system again and at the same time replace the rear pads at the next service.

It does sound like vacuum leak to me, too. Is this an inexpensive repair?
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Brian M. - 1998 S70GLT, 1998 S70 GTA

Brian,
I wrote what I suspected because I had a hiss too and it was this hose. It's not hard to replace and the dealer has this hose on a spool. You can get it by the foot and replace it yourself. It's the hose coming off of the brake booster (not on the brakes or brake's master cylinder), the so called brake's servo motor. I don't think it's the motor itself, but the vacuum line off of it. Here- reread my post here: http://www.brickboard.com/AWD/index.htm?id=1061442
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1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon. My cars have been running so well lately they've got me worried.

Thanks, man. I have a feeling it is the hose, too.
I feel much better!

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Brian M. - 1998 S70GLT, 1998 S70 GTA