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Car shimmy at under 7 mph

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by N7OKN, May 5, 2014.

  1. N7OKN

    N7OKN Junior Member

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    I thought this was normal but now I'm not sure. My '07 shakes when braking below 7 mph.
    Coming to a complete stop is never perfectly smooth unless medium to hard braking is required. My thought was that the MG2 is in creep mode even while my foot is lightly on the brake pedal, causing the jerking, but creep works properly while not braking. The shaking is very steady, at about 6 Hz, the same frequency as the "popping" noise one hears when stopped at the light with the foot lightly on the brake; just enough to keep the car from creeping, but not mashed far enough to turn off the creep current from the battery. I take it there's two sensors on the pedal as well as a potentiometer. Could the problem be mitigated if the creep current were cut off at the presence of a foot rather than having to press harder? There is no shaking on a harder stop, only the slow ones.

    Another thought I had was that the pressure pump itself is supplying the brake pressure to the friction pads, causing the pulsing. In a previous thread, we discussed why my pump was coming on so often. Perhaps a leak in the canister causing the pressure not to be buffered, and the pump itself providing the pressure.

    Some expert thoughts would be appreciated.
    .
     
  2. dolj

    dolj Senior Member

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    It could be that your rotors are rusty and causing the pads to bite. Above 7 mph you will not be using the brake pads for gentle braking, which is why you will be noticing it under 7 mph.

    You could try driving up to (no more that) 40 mph, select N gear and then apply your brakes positively until you come to a halt. Repeat three (or more) times as necessary. Selecting N will ensure you use hydraulic brakes and not regen. This should clean off the rust.

    Obviously, you will need to find a suitable place to do this.

    Report back on how you get on.


    PS, could you go back to your duplicate post and edit it to say Duplicate? Cheers.
     
  3. dorunron

    dorunron Senior Member

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    You can also click "Report" and simply ask the admin to remove it for you. Keeps the forum nice and clean that way.

    Ron
     
  4. N7OKN

    N7OKN Junior Member

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    First thing I did last night (report;delete request), now waiting for the delete. I will try the brake thing, thanks! I'll post on how it works. I am still curious, it is normal to hear a 6 Hz continual knock when keeping your foot on the brake lightly at a light and then for it to disappear when you mash hard enough to turn off the creep current form the battery?
     
  5. bisco

    bisco cookie crumbler

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    i've never heard a 6 hz knock, but i don't know what 6 hz is.:)
     
  6. dolj

    dolj Senior Member

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    I'm curious to know how you know it is 6 Hz?
     
  7. N7OKN

    N7OKN Junior Member

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    Hz=how many per second.
    I couldn't really count the pulses within one second, it's too fast. But you can create a pattern in your head, count the pulses in that pattern (I like to hear the beats in groups of three or six) and then determine how many times it repeats in 30 seconds. It's pretty close.
     
  8. JC91006

    JC91006 Senior Member

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    Are you sure it's not the pump noise from your other thread?

    SM-N900P ?
     
  9. usnavystgc

    usnavystgc Die Hard DIYer and Ebike enthusiast.

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    Yes this is normal. Happened all the time on my 06. Nothing to worry about.
     
  10. N7OKN

    N7OKN Junior Member

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    No, I'm not sure at all. that's why I'm asking. I pretty much suspect that's normal, but I suspect the pulsating just before the complete stop isn't. It will be 4:00 before I'm back in the car to try Dolj's suggestion.
     
  11. JC91006

    JC91006 Senior Member

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    A pulsating feeling from a warped rotor will not make a 6hz sound. Also if your rotors are warped, you most likely will feel it when you brake at high speeds and not speeds of 7mph or less. This sound you are hearing is covered under the discussion on the other thread mentioning the sound.

    First timer, '07 Pkg 4, 15 Days and counting, Strange noise

    Read more: http://priuschat.com/threads/first-timer-07-pkg-4-15-days-and-counting-strange-noise.140417/#ixzz30rLMF9Q0
    Follow us: @PriusChat on Twitter | PriusChat on Facebook
     
  12. usnavystgc

    usnavystgc Die Hard DIYer and Ebike enthusiast.

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    This pulsation he's talking about is when your completely stopped. If you don't have the brake pedal completely mashed, it will sometimes produce a slight pulsing sound. I have felt it before. If you mash the pedal down harder, it will stop.

    As for the other problem of 7-0 stopping, yes, try Dolj's suggestion.
     
  13. N7OKN

    N7OKN Junior Member

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    Thank you Usnavystgc. Well I tried stopping a number of times on neutral, and each time I still felt the pulsating. It may have gotten just a little bit better, but it's hard to know. I need to do some more friction stopping before I know for sure. I'll update when I know more.
     
  14. usnavystgc

    usnavystgc Die Hard DIYer and Ebike enthusiast.

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    Try this if you can, drive in reverse with one foot on the gas and one on the brake (in a big wide open parking lot or something. Since regen braking is shut off in reverse, you will use friction brakes the entire time.

    Additionally, check your rotors for rust and your pads. Sometimes the pads on these cars get so old, they fall apart.
     
  15. N7OKN

    N7OKN Junior Member

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    Neutral forward braking still uses MG2 for slowing?
     
  16. N7OKN

    N7OKN Junior Member

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    BTW Usnavystgc, thank you for your service.
     
  17. usnavystgc

    usnavystgc Die Hard DIYer and Ebike enthusiast.

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    No, neutral forward does not use any form of regen braking but, you cannot apply power while braking. In reverse, you can put one foot on the brake, one on the gas and really listen and get a feel for exactly what's going on with your brakes.