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Discussion Starter · #1 ·
I would like some opinions on a problem with my brakes. Also perhaps ideas to demo the problem to dealer if they pretend they can't find it.

My brake pedal has felt a bit spongy for the past few weeks. Brakes can still trip ABS on dry road if I stamp on them but if I roll into the pedal slowly and then try to brake hard, the pedal goes 3/4 of the way to the floor with only mild braking. Pedal feels like it might move even more but I didn't try that in case it damages MC seals. Today I tried the brakes with engine off and hood open. I get a distinct pssshhhh sound when I press the pedal but it stops when the pedal stops moving.

Is the noise just from brakes using vacuum from some reservoir or do I have a leak in booster? As for the soft pedal, it feels like when I stamp on the pedal, the emergency braking feature turns on and that's why it's strong braking. But when I roll into the pedal it's spongy and feels almost like leakby inside MC.

Background: '21 wrx base, ~18k miles, sliding calipers, fluid looks good and hasn't budged from max level. No changes to brake other than a MC brace. No leaks or damaged/bulging brake hoses. factory pads and rotors.
 

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Little Homie
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It will make a little sound from the master cylinder and abs module. It's just the nature of a hydraulic system..

If pad life is still good it would t hurt to bleed the system.
 

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Discussion Starter · #3 ·
I'll try that next, it's due at 24k according to manual. Can I bleed abs with an elm237 stick or does it need ssm4?

It doesn't sound like the whining/hammering noise typical of large hydraulics, more like old-school fireplace bellows.
 

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Little Homie
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I can't speak to the abs module specific bleeding needs on your car.

That does sound like a vacuum issue, but on a car that new?
 

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Discussion Starter · #5 ·
It is odd for the age. Recorded the sound but site won't let me upload so I've linked it. Maybe you hear something I don't.


Another odd thing, I changed to new tires today and the pedal is still spongy and moves too far but the weakness in brakes is gone. Even on damp roads they are uncomfortably strong. Maybe old tires were slipping & i just didn't notice abs light?
 

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Discussion Starter · #7 ·
The volume is almost the same as air escaping from an air mattress. I'll start with a fluid flush and keep listening if the sound changes.

Thanks for the help. Wasn't sure what to make of the noise.
 

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Little Homie
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Yeah I checked on my Jeep. I just did all the brakes on it and the pedal is stone solid, it does make that noise but not hole in air mattress loud. Is the fluid level good?
 

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Discussion Starter · #9 ·
Thanks for checking. Yes the fluid level is at max & fluid is clean. Just checked on a mazda3 & escape as well. Same noise but much quieter. I guess it's a normal sound & just louder on subaru than others. I'll get the brakes bled along with reverse switch recall. Hopefully that fixes the mushy pedal.
 
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