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Brake jittering at low speed when close to a stop....any thoughts?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by SingleDoggg, Jun 12, 2022.

  1. SingleDoggg

    SingleDoggg New Member

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    First off, my car is a 2012 Prius w/ 270K miles on it and I mainly use it for driving instructions. About 6 months ago I started to feel the brake jittering when it comes close to a stop approximately at 1-2mph(slightly pressing on the brake pedal while the car is still moving), I first thought it was the unevenness on the brake disc that causes it so I didn't really pay attention to it. And roughly 2 months ago as the jittering becomes worse, I finally decided to replace my brake pads and discs to get rid of the problem, but soon after the replacement I realize the problem still exists. I then replace the brake fluid but still, problem remains. And problem becomes worse recently as well, not only does the brake jitters at low speed with little pressure on the brake pedal, I started to hear knocking noise behind the pedals from time to time when I pressed on the brake pedal before switching gear.

    The problem concerns me a lot now because I don't know if it will cause a brake failure when a student and I are driving on the road. I bought the car back to the dealership to see if they can figure something out but the staff there told me they couldn't find any code relating to the brake system and they refued to take a further look even I insisted on showing them the problem in person. I tried to dig through every websites and forums but still haven't got any result, clueless now on where and how am I gonna have it fixed, any of you have any thoughs? Any comment will be greatly appreciated!
     
    #1 SingleDoggg, Jun 12, 2022
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  2. JC91006

    JC91006 Senior Member

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    A student driver car with 270k miles? Dang I thought these were locally driven??

    Does this car have 2 brake pedals? One on the passenger side as well?

    I'm not really understanding the "jitter" feeling, does it pulsate? Try braking while the car is in neutral, does the jitter come on sooner than right before you stop (2mph)?
     
    #2 JC91006, Jun 12, 2022
  3. bisco

    bisco cookie crumbler

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    might be the brake master cylinder going out
     
    #3 bisco, Jun 12, 2022
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  4. ChapmanF

    ChapmanF Senior Member

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    Can you make that keep happening, by holding a certain pressure on the pedal? Is the sound kind of like knock-squirt, knock-squirt, knock-squirt?

    That can happen if one of the valves in the brake actuator is not fully holding pressure. The car is trying to hold a steady pressure on the brakes, but the pressure is dropping off through the leaky valve, and the computer repeatedly has to pulse open one of the supply valves to squirt the pressure back up.

    After enough of that, it will have used enough pressurized fluid to need to run the pump again: knock-squirt, knock-squirt, knock-squirt bzzzzzt, knock-squirt, knock-squirt, knock-squirt bzzzzzt, knock-squirt.

    If that's happening, replacement of the actuator is probably in your future.
     
    #4 ChapmanF, Jun 12, 2022
  5. PriusCamper

    PriusCamper Senior Member

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    And because it happens below 6mph would it be safe to assume that if it's not disks or pads of the brake system, it's the valve that's specific to operating the mechanical brakes?
     
    #5 PriusCamper, Jun 12, 2022
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  6. SingleDoggg

    SingleDoggg New Member

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    Yup mainly drivin in local areas and yes it does have a second brake pedal on the passenger side as well.

    Pulsate is exactly what it happens, sorry English wasn't my first language I didn't think of that word. And I did try it once on a downhill where I put the car in neutral and test the brake, the pulsating did not come on until slow enough like 2mph. Thanks.
     
    #6 SingleDoggg, Jun 12, 2022
  7. SingleDoggg

    SingleDoggg New Member

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    Thanks for the idea! I only encounter the knocking sound couple times so far and I don't know what triggers the knocking sound, it seems like happening randomly. I will definitely go to a repair shop and ask them for an inspection and possibly a quote. And would it also be the cause for brake pulsating at low speed as well? Just wondering if replacing the actuator could solve both problem.
     
    #7 SingleDoggg, Jun 12, 2022
  8. JC91006

    JC91006 Senior Member

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    I want to understand what you've changed so far.

    1. new brake pads for front and rear
    2. new rotors for front and rear
    3. bleed brakes with new fluid (hopefully using software to do this)

    Are those the 3 things you've done?
     
    #8 JC91006, Jun 13, 2022
  9. SingleDoggg

    SingleDoggg New Member

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    Correct, except the software part on brake fluid changing, but the brake pulsates exist before and after the change so I think it has nothing to do with brake fluid, thanks.
     
    #9 SingleDoggg, Jun 18, 2022
  10. SingleDoggg

    SingleDoggg New Member

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    Quick update for people who might need it in future, problem solved after I replaced Brake Booster(47050-47190) and the Pump Assembly(47070-47060).
     
    #10 SingleDoggg, Aug 7, 2022
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  11. Russ s

    Russ s Junior Member

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    Same problem. Have to release brake pedal over bumps or brakes go out for a couple seconds, big pedal fade. Pump and stop again. Clunking raspy jittery noise at like 2 mph.
     
    #11 Russ s, Aug 10, 2022
  12. ChapmanF

    ChapmanF Senior Member

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    Doesn't really sound like the same problem as this thread.

    In fact, it sounds like two things: for what happens when lightly braking over bumps, see any of the existing threads on that, like this one from 2008. All Prii do that; have to get used to it, but after that it's not a problem. You don't have to release the pedal; just keep pressing. If you need to press a little harder to stop in the distance you intended, do that.

    Except for one thing: the normal transition delay is no more than a brief fraction of a second. It might feel like "a couple seconds", if you're taken by surprise and thinking "schezbzflat! what are my brakes doing?!" but only be a split second in reality.

    So it could be worth going back to a bumpy location, making it happen several times in a row on purpose, and paying calm attention to the delay. If it's really just a split second, that's the normal behavior. If you're really seeing delays of "a couple seconds", then you do have something weirder going on.

    As for the clunking raspy jittery noise at like 2 mph, maybe a different thread should be started to ask about that.
     
    #12 ChapmanF, Aug 11, 2022
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