Soft thumps when coming to a halt: first problem in 50k miles

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Eisenson, Mar 29, 2008.

  1. Eisenson

    Eisenson New Member

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    This is an '04, with just over 50k miles on it since purchase in October 2003 (yes, I'm an early adopter). It has the extended warranty until I die.

    The car's been quite perfect until two weeks ago, when I noticed a couple of quiet bangs as the car came to a stop. Sometimes it was one, sometimes two or three close together. We're quite sure that it's coming from the rear of the car, and probably from the right side. The sound is about what one would expect if there were a can of soda rolling about a foot in the plastic well. It's intermittent and unpredictable.

    The first step was to pull everything apart in the trunk and ensure that nothing was unsecured. I looked carefully for a lead ball under the seat. There was nothing even suspicious. The sound recurred.

    I took it to the dealer, who replicated the sound but could find no fault. They tightened everything in sight and sent me home. The sound recurred.

    I lifted the car, removed the rear wheels, deglazed the drums and shoes, blew everything out, inspected all visible welds, shook/twisted everything that moves, and reassembled - torquing the wheels properly. Both of the wheels are intact and unbroken. The sound recurred.

    Any ideas from this crowd other than earplugs?
     
  2. qbee42

    qbee42 My other car is a boat

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    Some questions:

    1) At what speed do you hear the thump?

    2) Does it happen with both hard and soft braking?

    3) How about coasting to a stop?

    4) Do you get the thump if you switch to N and then brake to a stop?

    Tom
     
  3. Eisenson

    Eisenson New Member

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    THANKS, TOM -- GOOD QUESTIONS!
     
  4. qbee42

    qbee42 My other car is a boat

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    Since it happens at low speed, it is probably a friction brake issue. The sound coming from the back suggests the drum brakes. I would look at the adjuster assemblies in the rear drum brakes. I imagine the brake shoes are shifting.

    Tom
     
  5. JimboK

    JimboK One owner, low mileage

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    I would hope the dealer's not just blowing you off. Since you have the extended warranty, I would insist on them digging deeper until they find the problem. If they're able to replicate it, they should be able to fix it, IMHO.
     
  6. edthefox5

    edthefox5 Senior Member

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    First thing I thought of was a bad front strut as I had the same problem on another car but you seem sure its in the back. Try this dopey test. Maybe get someone to drive the car and you standing there at a quiet place have them come to a stop right next to you. That way you can at least make sure its really out back. If out back not much there. Brakes...bearing..shock. Maybe lightly lubricate the brake shoe pivot points and the self adjuster mech. with some grease. I'd throw a new set of high quality shocks out back as a start if it turns into a real head scratcher. Or at least take that side shock off and test it for proper compression. Good luck.
     
  7. Eisenson

    Eisenson New Member

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    It looks like qbee was right: friction brakes. I pulled both rears apart, cleaned (grit, dirt, of which some was in the self-adjust mechanism!), and reassembled. I had already deglazed all surfaces.

    Today I tried more 50+ stops with various levels of pressure, in drive and in neutral, and was unable to duplicate the problem.

    Thanks!
     
  8. hobbit

    hobbit Senior Member

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    I've had that problem for a year + now, and went through all
    kinds of diagnostic hell trying to find it. It's definitely
    in the back, definitely only happens when you come out of
    regen braking onto the physical binders, and often *doesn't*
    happen when you're trying to force physical braking in both
    directions by scooting back and forth, moving to Neutral, and
    stopping. I've had the car up in the air, with the suspension
    both weighted and not weighted, pounded on everything with a
    rubber mallet trying to find something lose, and I'll be buggr'd
    if I could ever find the problem. I wouldn't rule out struts
    or bushings or whatever, but so far there's been nothing
    obvious that I could find even with the number of times I've
    been all over the brakes in the past.
    .
    Lately, or at least over the winter, it seems to have diminished,
    so it may be temperature related. Since I mostly hear it through
    the body of the car, that's not due to windows being closed
    or open.
    .
    Just last night I was driving someone else's '05 briefly, and
    heard a hint of the same thing going on.
    .
    This is, in fact, what gave rise to a minor addition to one of
    the training slides to try and get the reader thinking about
    diagnosing hybrid braking systems the right way --
    .
    _ Customer: I hear a klunk when I'm braking.
    _ Tech: during regen or physical?
    _ Customer: Huh?
    .
    _H*
     
  9. Eisenson

    Eisenson New Member

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    It wouldn't surprise me to hear the problem today, but since no one reports the sound as a precursor to some disaster I'm not particularly troubled by it.

    Hobbit: I'm pleased that this isn't a club of one, and that you're so skilled. Take the lead, my friend, and if you think of diagnostics I might do let me know.
     
  10. may all be happy

    may all be happy New Member

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    I had this problem with my 2007 since it was new. The symptoms occurred as the car went from about 5 mph down to zero. Thump, thump, thump. Recently I upgraded my Integrity tires for Triple Treads and the problem went away. Don't know what was causing the problem. Maybe the Spare was loose.
     
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