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New break feels "stuck" at very low speed (almost dead stop)?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by 2009Prius, Mar 26, 2009.

  1. 2009Prius

    2009Prius A Wimpy DIYer

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    New brake feels "stuck" at very low speed (almost dead stop)?

    I just got a brand new 2009 Prius last week. I noticed sometimes right before coming to a complete stop, the brake seems getting stuck, letting go, getting stuck again, and letting go again, back and forth. Today while behind a long line of cars waiting for the traffic light I noticed a similar feeling when the car starting from a dead stop and gliding forward very slowly with my foot riding on the brake pedal. I think the speed is less than 5 mile/hour when these happened.

    I usually brake lightly to let the car stop smoothly, and at the last second ease the brake a little to avoid throwing the passengers forward. I think the "sticking" happens during the easing of the brake at the last second. It feels as if the brake pads jump between being firmly compressed against the rotors and being (suddenly) released from the rotors.

    Is this just the new brake pads haven't worn enough to match the rotors or something I should worry about? :confused:

    Thanks!
     
    #1 2009Prius, Mar 26, 2009
  2. qbee42

    qbee42 My other car is a boat

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    Like many other systems, the brakes on the Prius are a little different than on normal cars. The Prius uses regenerative braking when it can, and switches to normal friction brakes when going too slowly for regeneration. The transition is at about 7 mph. During the transition from regenerative braking to friction braking, it can feel like the brakes let up a little, and then grab. This is normal.

    One problem with the friction brakes on the Prius is that they don't get much use. This makes them last a long time, but they also get rusty. Rusty brakes can be noisy and grab when you stop. If your brakes start to do this, you should clean off the rust with a little forced braking. On an empty road, take your Prius up to 40 mph or so, shift to N, and then brake until you slow down or stop. Shift back into D and repeat the process a few more times.

    Braking in N forces the Prius to use the friction brakes, which helps clean off the rust.

    Tom
     
    #2 qbee42, Mar 26, 2009
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  3. thedutchtouch

    thedutchtouch prius is my SUV

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    excellent reply! i just noticed this on my prius as i was driving home, and came to the exact same conclusion. it works fabulously (although i only did it from ~20 to ~5 mph, still did the trick)
     
    #3 thedutchtouch, Mar 26, 2009
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  4. qbee42

    qbee42 My other car is a boat

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    Thanks. The speed isn't critical, you just need enough to do the cleaning.

    Tom
     
    #4 qbee42, Mar 26, 2009
  5. jayman

    jayman Senior Member

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    To the OP: do you park outside? As Tom noted, rust on the rotors cause problems as the friction brakes don't get used much

    I park in a heated attached garage. The most I have noticed is an extremely light film of rust.
     
    #5 jayman, Mar 26, 2009
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  6. calabrsn

    calabrsn Junior Member

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    I get the same unsmooth "grabbing" feel with the friction brakes when coming to a complete stop. If I clean the brakes by a little forced breaking, using neutral and braking at higher speeds, the grabbing goes away but it comes back in a very short time. I just figured it was a normal symptom for the Prius.
     
    #6 calabrsn, Mar 26, 2009
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  7. Frayadjacent

    Frayadjacent Resident Conservative

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    I haven't noticed this in my new 09 Prius. But then, a few years ago, I had an Insight, and got used to the feel of the brake pedal, so I just may not be noticing. And the car has 'brakes' not 'breaks'. Break means to destroy. Don't destroy your Prius! ;)
     
    #7 Frayadjacent, Mar 26, 2009
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  8. 2009Prius

    2009Prius A Wimpy DIYer

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    Hi Tom, Thanks a lot for the tip on using "N" to wear away the rust. I tried a bit (it was raining so didn't do a lot) and did notice a big difference when braking in "N" (quite smooth) and braking in "D" (stick and slip) when nearly dead stop. I suppose the electric motor put out pretty large torque at very low speed?

    Today when driving a Honda Odyssey I also noticed a slight stick and slip of the brake (much less severe) so I am pretty convinced it is the mechanical brake, not the regenerative one. I am also less worried now.

    Thanks again! :)
     
    #8 2009Prius, Mar 27, 2009
  9. 2009Prius

    2009Prius A Wimpy DIYer

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    Hi Jayman, Thanks for the comments. I park outside during the day and inside at night. The car was made in Dec. 08 and bought March 09 so it had been sitting around and rust could have formed.

    How do you tell if there is a film of rust? Can you see or feel something? I did look at the surface of the front rotors. There are some concentric rings of gray or black color but the surface feels very smooth to my fingers.

    Thanks! :)
     
    #9 2009Prius, Mar 27, 2009
  10. 2009Prius

    2009Prius A Wimpy DIYer

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    Hi Frayadjacent, Thanks for pointing out the spelling error. I will see if I can fix it. :)
     
    #10 2009Prius, Mar 27, 2009
  11. 2009Prius

    2009Prius A Wimpy DIYer

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    Hi calabrsn, Thank you for sharing your valuable experience. I feel much safer now. Thanks! :)
     
    #11 2009Prius, Mar 27, 2009
  12. 2009Prius

    2009Prius A Wimpy DIYer

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    Update: Today I found the stick-slip problem is gone! I didn't expect the small amount of braking with "N" would make such a difference! :rolleyes:
    Thanks again!
     
    #12 2009Prius, Mar 27, 2009
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