Could this be the new braking vibration?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by MrPete, Oct 26, 2025 at 10:38 PM.

  1. MrPete

    MrPete Active Member

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    I just noticed that when braking on a very smooth road, I feel a rapid vibration, I think in the brake pedal.

    Been a couple of years since I replaced pads. Never touched nor measured rotors... And never worried about runout.

    Time to break out the shiny new toys my kids got me! Micrometer and magnetic base+nice dial indicator.

    A) I need a base with a longer arm and stronger magnet. Mounting is a pain!

    B) Here is what I found:

    * Front rotors are at 23.1 mm (min 22)
    * Rear rotors are at 7.8 mm (min 7.5)
    * Runout is approx 0.1 mm (max 0.05) on all four wheels... Within a few hundredths.

    What I see on runout is two high spots about a third to halfway around the rotor, the the rest is mostly low (ie high at 0 to -0.01 mm, rest -0.07 to -0.10)

    My questions:

    * could runout like that cause the vibration?
    * would you just replace rotors?
    * since I never measured this when pulling/replacing rotors in the past (and didn't have vibration issues),is it possible this is a new issue, or would it have shown up long ago?

    And finally, just had a (dumb?) thought: If the caliper pins are not sliding properly, would that, combine with runout,cause vibration (maybe the whole thing fixable by greasing pins and trying the five-position runout test LOL?)
     
    #1 MrPete, Oct 26, 2025 at 10:38 PM
  2. PriusCamper

    PriusCamper Senior Member

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    Great to see you're getting back under your car this Fall! :) I've never experienced these symptoms on a Prius. What about the classic Prius problem of brakes grabbing too hard on a light push? Has that come up at all?
     
    #2 PriusCamper, Oct 27, 2025 at 12:18 AM
  3. MrPete

    MrPete Active Member

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    Nope.... Not an issue.

    Would you consider 0.1mm runout basically close enough?

    It's not a horrible vibration. Just noticeable enough that I decided to check.
     
    #3 MrPete, Oct 27, 2025 at 9:26 AM
  4. Tombukt2

    Tombukt2 Senior Member

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    Properly sliding pins and not old worn out cooked pads are always good . Many of the Prius I buy the pads are cooked from time and heat they even look like crap . Cause they in place soooo loooong.
     
    #4 Tombukt2, Oct 27, 2025 at 9:31 AM
  5. MrPete

    MrPete Active Member

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    When I get some more Round Tuits, I still need to finish building my semi automated HV battery module tester/script. That will be fun!

    I also did a separate upholstery project. Learned how to identify and source correct fabric and glue/staples. Replaced the gross center console top. Driver seat edge and maybe more still to come
    Maybe should write it up...
    17615718545523374897612476313424.jpg
     
    #5 MrPete, Oct 27, 2025 at 9:31 AM
  6. Danno5060

    Danno5060 Active Member

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    Outstanding job on that console top. Those Gen 3s really did get pretty gross looking after a while. Would love to have a replacement for mine in a Pleather or vinyl rather than that worn out cloth one I've got.
     
    #6 Danno5060, Oct 27, 2025 at 1:16 PM
  7. PriusCamper

    PriusCamper Senior Member

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    I agree... And I know OP only likes to post under the car stuff, but I'm very keen to "Learn how to identify and source correct fabric" for my Gen2. Can you elaborate @MrPete ?
     
    #7 PriusCamper, Oct 27, 2025 at 1:28 PM
  8. MrPete

    MrPete Active Member

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    I guess that fits the Maintenance topic. Will do :)
     
    #8 MrPete, Oct 28, 2025 at 1:36 PM
  9. MrPete

    MrPete Active Member

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    Still wondering, could the vibration come from 0.1mm runout, or am I barking up the wrong tree?
     
    #9 MrPete, Oct 28, 2025 at 1:37 PM
  10. Danno5060

    Danno5060 Active Member

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    Only a wild guess here.

    I used to have an older GM. One of the ones where they were just going to the transverse-mounted engine. That car originally worked normally, but after about a year or so, a braking problem would occur. Especially when someone would cut me off on the freeway. I'd have to brake hard, and the steering wheel wobbled dramatically. The more I had to brake, the more the steering would wobble. It was sometimes a hell of a ride. Getting the brakes done would fix the issue - for a while, then it would start happening again.

    My guess at the problem was that the oil filter was near one of the front brake discs, and sooner or later, an oil change "technician" would get some oil on the nearby disk, causing it to either start to grab in one spot, or it to warp because of the uneven heat distribution.

    I don't know if this is related to your issue, or if this was actually the cause of my problems. That was around 30 years ago.

    Maybe make sure your pads and drum are free of any oil or other contaminants. Some may disagree with this, but take a sander to the disc surfaces. Not to sand them smooth but rough up the surface a bit. Then go through a break in process similar to this:

    What is the Break-In Procedure? - PowerStop Brakes

    This may not be your problem. I don't know how prominent your vibration is, and I'm making a few assumptions here.
     
    #10 Danno5060, Oct 30, 2025 at 10:31 AM
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