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Brake needing to pressurize every time I brake

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by badbrakes1998, Oct 6, 2020.

  1. badbrakes1998

    badbrakes1998 New Member

    Joined:
    Oct 6, 2020
    7
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    Location:
    Delaware, Ohio
    Vehicle:
    2010 Prius
    Model:
    Two
    Hi everyone, I think my Prius is having some issues.
    Yesterday, my father and I replaced the pads, rotors, and calipers on my rear axle.

    We have never done this on a Prius, and since we're idiots, we decided to do it without looking up any of it. We realized that bleeding the brakes would probably be different than a normal car, so we looked it up online and everything was talking about using a scan tool. I had to get to work in an hour, so we decided to just go ahead and bleed the brakes by sucking the air out of the bleeder with a tube, closing the bleeder each time the tube was full. Reservoir did not go below low the entire time and we filled it up a bit. The brakes had a leak where the brake line entered the caliper, but we fixed that and continued sucking fluid through. Eventually, we would get 3 inches or so of no bubbles, so we closed the valve and called it good.

    Now, on to the problem:

    Right when I hit the brake, I realized the brakes had an issue. When I depressed the brake pedal, there was a noise that was much louder than I am used to when I brake. Normally its a quiet whoosh noise, but this time it was a much louder one. I figured that maybe there was some air in it still, but if I drive it around it would work its way out possibly. I let it sit for two days and I drove it around just 10 minutes ago for a few miles, braking hard to try to figure out what the issue is.

    The issue is that when I brake, the brake does not actually start to stop the car until the whooshing noise is done. This takes approx. 3 seconds, and if there is more than 15 seconds or so between braking, it has to pressurize (I assume this is what it's doing) every time I brake.

    Anyone have any idea whats going on? There are not lights on or anthing.
     
    #1 badbrakes1998, Oct 6, 2020
  2. Rebound

    Rebound Senior Member

    Joined:
    Mar 11, 2010
    3,970
    2,618
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    Location:
    Portland, OR
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    The hybrid design means sometimes the engine doesn’t run, so a Prius doesn’t use and vacuum lines. The brake booster is electric, not hydraulic, and must be turned off before a brake bleed.

    Here’s a video which shows the proper procedure:



    Second thing: IMPORTANT: The rear brake calipers have a raised cross-like surface on the piston. The back of the brake pad has a raised nub which must fit inside this cross, like in the bottom of a V. Understand? You may need to rotate the piston so that the brake pad will fit properly.
     
    #2 Rebound, Oct 10, 2020
  3. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    24,912
    16,215
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    Yes: needs to be bled.

    There really isn't any way for air in the lines to "work its way out". You have to open bleeders and let it out.

    So you were in a hurry and didn't have Techstream so you put it back together and drove it with air in the lines. You got away with that better than you would in a conventional car. With that much air in the lines in a conventional brake system, you simply wouldn't be able to stop. It kinda sorta works in a Prius because there's a pumped-up accumulator full of pressurized fluid that the car can let whoosh into the lines and take up the air space. (Then when you release the brakes, the air expands again, shoving all that fluid back to the reservoir, and the electric pump has to run again to refill the accumulator.)

    But as you've noticed, that doesn't give you very good braking, and beyond that, if there is ever a glitch that switches your brakes to fail-safe operation, it will be just like a conventional system with air in the lines, and you will not be able to stop.

    So now that you have gotten where you needed to go and back when you were in a hurry and didn't have Techstream, get your hands on Techstream and bleed the brakes.
     
    #3 ChapmanF, Oct 10, 2020
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