Hiss or pfft when pressing brake pedal

[kwk442]

Hello Yaristas.

I recently bought a 2010 Yaris sedan, automatic. Shortly after buying it, the front brakes started squeaking. I serviced the front brakes. Then the rear brakes started squeaking. So today I decided to address that.

The rear drum shoes still had some meat on them so my goal was to clean everything off and lubricate the touch points.

After reassembly, the brake pedal was engaging pretty low. I had screwed in the adjusters to try to make it easier to take things apart, so I wasn't that surprised that they would need some adjustment. I ended up doing several rounds of adjustment. At some point along the way I decided to see if I could get the adjusters to adjust on their own by braking in reverse or using the handbrake. The star adjusters are super clean and well lubricated so I figured this would be the prime opportunity for them to actually work, but I pumped the brake hard and only got a few clicks out of them -- not nearly enough. Anyway, while doing this I started noticing a hiss or pfft sound, but I couldn't quite tell where it was coming from. With my wife's help as a brake pumping assistant, it seemed that some of the noise was coming from the vicinity of the brake booster and master cylinder. I also heard some noise near the rear drums but that may just have been the pistons activating normally.

Anyway, after adjusting a million times, I got a usable brake pedal, but the air escaping sound is still occurring.

Other data:
* If I kill the engine and pump the brakes, the brake pedal feels pretty firm. There's definitely still some amount of slack before everything is fully engaged however.
* If I then start the engine while holding the brake pedal, the brake pedal sinks a bit and then stays there.
* It feels like the brake booster is functioning.
* Sometimes when I'm stopped at a traffic light, the car vibrates a bit. One time when this was happening I pulled the handbrake and left off the brake pedal, and the vibration decreased.

So what does all this point to? Was the brake booster starting to fail and I helped it along a bit? Did I somehow introduce air into the brake lines? (I don't know how this would have been possible but I was pretty ham handed with removing some of those drum brake springs.)

Thanks for your suggestions and expertise.

[kwk442]

Evidence:
https://youtu.be/Kd6b8wo7DqU

[kwk442]

My wife & I bled the brakes just now and everything seems good again. So, apparently one can introduce air into the brakes by futzing with the rear drums. I was not aware.

[harry56]

K&N Cold Air Intake, Megan Racing MO-E Muffler, DNA Motoring Exhaust Headers, Pedal Commader throttle controller, NST Pulley Kit, STR 526 17x8.25 rims (Volk TE37 Replica).


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