Strange hissing from brake pedal after pad job

#1
So two weeks ago i changed rear brake pads to my 2004 Corolla and when job was done and i was pumping the pedal i noticed that pedal started to hiss. Brake job was normal to me. Old pads were so thin that the piston inside of the caliper was pushed out. So i had to push it back with C-clamp. Before doing that i opened the cap of brake fluid reservoir. Piston went in and i changed pads. Did same to the other side. When job was done the brake fluid was over the max level at the reservoir, so i took some fluid out with syringe. Then i closed the cap and went to pump pedal and it was hissing. Any suggestions what happened? Other than that the brakes and pedal works normally (did some brake booster tests with the pedal) and there isn't any fluid leaks. So im pretty confused here.

And I took my car to local Toyota dealer/mechanic and they said that this sound is normal. How can it be normal if it didn't occur before? I'm reluctant to accept that. Before this pad job, the pedal was silent. I remember this well, because few months ago i changed font pads and i did everything same way as this time and pedal didn't make any extra noises then.
 
#3
Yep im suspecting failing brake booster too. But on the other hand Toyota mechanic said that sound of bad brake booster is loud and often constant and the pedal turns stiff. In my corolla sound is mild air woosh and the pedal is normal. It brakes easily now with the new pads. So bit confusing.
 

Dano

New Member
#4
Mine was making a definite hissing sound but never a hard pedal.
I did notice that the pedal was not returning to it's normal height.
I replaced the booster before it got any worse.
 
#5
Mine was making a definite hissing sound but never a hard pedal.
I did notice that the pedal was not returning to it's normal height.
I replaced the booster before it got any worse.
How loud was that sound that your pedal made? Mine is some what quiet, just little woosh air sound. For example you can hear it only when doors and windows are closed, you are parked, radio/ac off and then you press the pedal and hear it.
 
#8
By pushing the pedal different ways with engine and power on and off. But im not sure how accurate those tests are and could you diagnose booster what is starting to fail. Maybe then when its broken.
 
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