"kind of" a Brake Question

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by cyberpriusII, May 27, 2011.

  1. cyberpriusII

    cyberpriusII Maybe it was the roses

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    My Prius is now at 31K. :eek:

    I tried to log-in and ask this Tuesday, but PriusChat apparently was grumpy that day and loaded me down with malware (see post in Fred's for details).

    Anyway, I don't think this is a real problem, but I noticed a few times in the past few days that when I had my foot on the brake for a "bit of time" that the pedal would sink slowly to the floor. Like it was being pushed through marshmallow foam --- YUMMMM.

    OK, I'm a scientist and I realize my vague language is not a help here. So, my best guess is that three times in five days of driving, which probably means in 60 miles of driving -- at most and probably less -- this has happened. This happened probably two seconds after a full and complete stop, while foot was still on brake.

    Having had a "like" problem in my old Corolla a few years ago, I checked the brake fluid and it is fine. I DID NOT crawl under and check the bleeder connections at the front wheels, which was the problem with my old Corolla (and, which, I proudly fixed myself). Not sure the Prius has those anyway, but it probably does:confused:

    So, this has happened about three times in the past week or so. I don't remember this happening before. Pretty much, this does NOT happen. Brakes work fine. Fluid is fine. I don't really want to crawl under -- it is a tight fit.

    Any thoughts? I know, brakes are important, but the Prius brakes are not really brakes, usually, right...:confused:
     
    #1 cyberpriusII, May 27, 2011
  2. jdenenberg

    jdenenberg EE Professor

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    Get Thee to the dealer. You probably have a problem in the brake hydraulic system.

    Your Prius simulates standard brake pedal pressure using the hydraulics when doing regenerative braking, and reverts to the friction brakes under several conditions:

    • Under 7 mph
    • Quick/hard braking (sudden stop)
    • ABS (avoid loss of directional control when braking)
    JeffD
     
    #2 jdenenberg, May 28, 2011
  3. xpcman

    xpcman Senior Member

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    Don't try to bleed the brakes yourself. I understand it takes special equipment that only the Toyota dealer has.
     
    #3 xpcman, May 28, 2011
  4. cyberpriusII

    cyberpriusII Maybe it was the roses

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    Hey, thanks for the responses. I think I am going to wait a bit and see what is happening. It has only happened a few times and I was distracted each and every time it did happen, so I may not have "experienced" what I thought I experienced.

    OTOH, I have been riding my mountain bike for three hours a day or so for the last few weeks, since Oregon's high summer is now here (only rains 23 hours a day). So, maybe it just my newly toned legs! LOL!

    BTW, I have never attempted to bleed brakes myself, although I have read the instructions. It seems like a real easy task. I wonder why the Prius would be different.
     
    #4 cyberpriusII, May 28, 2011
  5. seilerts

    seilerts Battery Curmudgeon

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    That's an indication of a serious malfunction, either air in the hydraulic system or an internal master cylinder leak. But no brake warning light when it happens? Strange. Anyway, your dealer should fix it for free under warranty. Do not wait, since a failure in the electronic brake control would disable regenerative braking, and leave you with hydraulic brakes that seem not to be working correctly.
     
    #5 seilerts, May 28, 2011
  6. jdenenberg

    jdenenberg EE Professor

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    There are a number of computer controlled valves in the Prius hydraulic system that get in the way of a normal brake "bleed". The dealer has an interface and software to cycle these valves as needed.

    JeffD
     
    #6 jdenenberg, May 28, 2011
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