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Violent EM disengagement slowing at 9 mph

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by szabi, Nov 3, 2009.

  1. szabi

    szabi I also have a 2007 Prius

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    Prius 2008, 17.5K miles. I am an engineer & have put 25K miles on 2 Priuses since 2007.

    The car is completely warmed up, pavement is dry and clear, weather is mild, temp. 60F. I am coasting in Drive, beginning at 30mph, towards a stop sign with foot off the accelerator. I apply the brake at 20mph. As I pass through the transition from regenerative slow-down to brakes at 9 mph, there is a single violent shudder through the drive train, but no sudden slow-down. I am aware of what the normal transition is like; this is about 10 times more violent, really disturbing. There is no bang or other noise.

    This has happened twice in 3 weeks, at 2 different locations. No indications from the monitor lights or other readouts.

    Has anyone else experienced this? Any diagnosis or advice?
     
    #1 szabi, Nov 3, 2009
  2. qbee42

    qbee42 My other car is a boat

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    This sheds suspicion on the friction brakes. I can't see where the HSD would cause this, but it is easy to see how a friction brake problem could cause a shudder at the transition.

    Tom
     
    #2 qbee42, Nov 3, 2009
  3. szabi

    szabi I also have a 2007 Prius

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    Quite possibly. But why would it occur rarely and intermittently? If it IS a brake problem, I would suspect a problem with the brake boost actuators or their controls.
     
    #3 szabi, Nov 3, 2009
  4. Celtic Blue

    Celtic Blue New Member

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    Have you tried making it do this at low speed in neutral? Since it is intermittent it would be hard to prove the negative, but if it did it while in neutral you could isolate the problem to the friction braking system.

    Maybe there is some stickiness on the rails/mechanism of the friction brakes (sand/gravel/flash rust.) You might be able to clear this with some solid braking in neutral from moderate speeds.
     
    #4 Celtic Blue, Nov 4, 2009
  5. szabi

    szabi I also have a 2007 Prius

    Joined:
    Nov 11, 2007
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    Location:
    200 mi N of SF Bay area
    Vehicle:
    2008 Prius
     
    #5 szabi, Nov 4, 2009
  6. richard schumacher

    richard schumacher shortbus driver

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    Presumably you have experience with Prius brake grabbiness in damp weather? and this ain't that?
     
    #6 richard schumacher, Nov 5, 2009
  7. qbee42

    qbee42 My other car is a boat

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    These are my thoughts as well.

    Tom
     
    #7 qbee42, Nov 5, 2009
  8. szabi

    szabi I also have a 2007 Prius

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    Definitely not. Tnx.
     
    #8 szabi, Nov 8, 2009
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