I noticed a hissing noise coming from under the dash
I noticed a hissing noise coming from under the dash while driving. I turned off air and
radio and noticed it was only when I pressed the brake pedal (didn't matter if I was
stopped or moving). When the car is stopped and its *Really* quiet I can hear it when I
am not pressing my brakes. I know this sounds like a booster issue but here is the catch:
My brakes are perfectly normal and have been for a week since this has happened. The
mechanic I spoke with does not believe its the booster, and I hope it isn't because I don't
have that money. The car is a 1999 Toyota Solara V6 SLE
Hmmmm. How dose the rubber hose from the block to the brake booster look?
BoholMark, It's as old as the car is. I tried running my hands up and down the hose to detect leaks but I couldn't find anything (granted there is a much more methodical way to do this). I suspect it could also be a the check valve. When I am in my car its easy to hear, left side under dash. But when I get under the hood, it is hard to pin-point the location of the noise with all the other moving parts creating noise.
If you leave it overnight is the brake peddle hard in the morning?
Mark, Yeah. Brake pedal gets pretty much hard when the car cuts off. Once car turns on, it operates normally and drops a couple inches.
Did the mechanic physically look at the booster or just give an opinion?
He gave an opinion. He said he'd worked on Toyota for 20 years and has only ever had to replace a few boosters and said he very highly doubted it given my symptoms.
All the symptoms are there. Hissing noise. The brake peddle gets hard. There's a vacuum leak somewhere.
I completely agree but I've read through so many posts that talk about bad boosters and I just struggle to think that's my issue... I have no trouble braking, no trouble idling, etc. It sounds like someone is going to have to take a look to diagnose... Thanks for your help!
I have the exact same problem on the same model/year car. Although the brakes seem to work normally, on a panic stop you can tell they are not providing enough braking power. At 40MPH and standing on the brake with both feet, ABS never engages and stopping distance too long. I took this to Toyota, and they did a full diagnostic on the brake system, including vacuum check of the brake booster. They found no problems. Funny thing is, the problem disappeared for a few weeks. No noise, and panic braking performance was restored, with ABS functioning as expected. But now it has returned. I am at a loss.
With the car running you can pinch off the brake booster hose and stop the vacuum to the booster. If the nose stops it is a booster it may be in the early stages of failure with a small pin hole in the diaphram.
I dont think it is the vacuum line going to the booster because your car would have had a rough idle.