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Subtle thump when coming to a stop?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Slice of the Jungle, Feb 27, 2012.

  1. Slice of the Jungle

    Slice of the Jungle Junior Member

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    I'm not even a Prius owner yet but have test driven 5 used ones in the last few days. The thing that is bugging me is a very subtle thump when coming to a stop. I noticed it on an 06 with 77k mi and also an 08 with 45k. I am more curious about the 08 as it was more noticeable and I drove the car quite a bit trying to figure out the sound, when I would slow down from about 35mph just as the car was at 3mph just before coming to a complete stop(and coming to a normal/gentle stop, not jamming on the brakes), there is a little thump. To me it sounds like possibly one of the electrical motors is stopping it's rotation and causing it, or maybe the braking system. When I abruptly stopped it would not occur. When I would slow from just 15mph to a stop I did not notice it. The 06 with 77k almost seemed like it would make the same sound but do it two or three times while gently braking and much more subtle than the 08. Thanks in advance for any help, Tim
     
    #1 Slice of the Jungle, Feb 27, 2012
  2. cwerdna

    cwerdna Senior Member

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    Unfortunately, since I'm not driving those cars, I can't tell you if it's normal or not.

    My 06 Prius w/61K+ miles still does a slight stuttering in the last couple of mph before 0 while doing light braking. I'm totally used to this now. I posted about it when I was a newbie at http://priuschat.com/forums/gen-ii-...tter-right-before-car-stops-4.html#post198335. Just for kicks, you could try shifting to neutral before braking to see if there's a difference. You won't get any regen if in neutral.

    You could also intermittently hit a rough engine shutdown. It's normal and isn't easy to repro at will. I believe it's easier to repro when the engine's cold. One of my posts is at http://priuschat.com/forums/gen-ii-...-troubleshooting/93532-rough-engine-stop.html. There are tons of threads on this such as the one at http://priuschat.com/forums/local-prius-club-main-forum/37051-rough-engine-shut-down.html.
     
    #2 cwerdna, Feb 27, 2012
  3. uart

    uart Senior Member

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    It's probably related the transition from regenerative to friction braking. The speed you're traveling and the deceleration rate probably determine exactly where the transition occurs and how abruptly.
     
    #3 uart, Feb 28, 2012
  4. fotomoto

    fotomoto Senior Member

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    Another vote for transition from regenerative braking to conventional braking. It's not always seamless.
     
    #4 fotomoto, Feb 28, 2012
  5. cwerdna

    cwerdna Senior Member

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    A suggestion about the above is to drive around w/the windows down and listen to see if if the "thump" coincides w/the gas engine shutting down, esp. when it's not totally warmed up. If so, I wouldn't worry about it.
     
    #5 cwerdna, Feb 28, 2012
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  6. edthefox5

    edthefox5 Senior Member

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    Listened to my 07 on the way home tonight and no thump braking in any mode at any speed.
    I also put it in neutral at 30 mph's and came to a stop a few times. No thump.

    Be aware if your test driving a Prius that has sat outside and not being driven for a few days the brakes will be messed up. You will hear some grinding and they will also catch bad.
    The car does not like the fine coat of rust we get on our rotors and the brakes get grabby if the car sits for a while outside.
    The rust goes away quick but its an issue we have all learned to live with.
     
    #6 edthefox5, Feb 29, 2012
  7. Slice of the Jungle

    Slice of the Jungle Junior Member

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    Thanks for all of the input, after checking out those posts cwerdna, and driving several, I'm chalking up the sound to a quirk with the vehicle. My biggest concern was that I drove two 08's with similiar mileage and one did it and one didn't. I am going to buy an 08 with about 44k miles, can't wait to get behind the wheel again, Thanks everybody
     
    #7 Slice of the Jungle, Feb 29, 2012
  8. fuzzy1

    fuzzy1 Senior Member

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    Mine (different generation) has always had something matching OP's 'thump' description, but it has never been bothersome enough to track down. It is clearly distinct from the regen->friction braking transition. I'll start watching the ScanGauge for any correlation to engine shutdown.
     
    #8 fuzzy1, Feb 29, 2012
  9. Wimble

    Wimble Junior Member

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    The car is full of little quirky noises if you're used to a standard gas guzzler. :)

    When first had mine I often found myself noting every little click and buzz due to the complete absence of the usual engine drone.

    I am throwing my hat into the switch from regen braking to friction as well by the way!
     
    #9 Wimble, Feb 29, 2012
  10. qbee42

    qbee42 My other car is a boat

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    I've seen this in gangster movies. Have you checked for a dead body in the trunk?

    Tom
     
    #10 qbee42, Feb 29, 2012
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