Can the brake rotor go bad without the pad going bad?

Discussion in 'Prius c Care, Maintenance and Troubleshooting' started by Species5618w, Jul 18, 2021.

  1. Species5618w

    Species5618w Member

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    During my last oil change for my 2012 Prius C, my dealer said the brake rotor is at 30% and I need to get it replaced. I am confused. I always thought it's the pad that would go bad first and only if you didn't change the pad in time, the rotor would get damaged. How come the pad is fine (still the original after 8 years) and the rotor needs replacing? I have never heard any braking noise indicating metal on metal. I said no but am a little worried.
     
  2. bisco

    bisco cookie crumbler

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    it is possible due to corrosion. but i would want them to show me each sider with a caliper on it.

    get a second opinion. have the brakes inspected, but don't tell them what the dealer said.

    i am not sure what 30% means, but i would think the pads would be in rough shape
     
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  3. Salamander_King

    Salamander_King Senior Member

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    As @bisco pointed out, it is possible to have the rotor goes bad before the pads due to corrosion or other reasons. If the rotor needs to be replaced, I am sure it would be a good idea to change the pads as well. The cost would not increase that much. I have never done brake jobs DIY. But, in all of the brake jobs, I have had on our cars (not on Prius) either at a dealer or at an independent shop, they always replaced both rotor and pads regardless of the amount of pad left.
     
  4. PriusCamper

    PriusCamper Senior Member

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    Classic making up unnecessary work scam... Because Prius uses a generator to make electricity when you use the brakes it's common that the rotors don't get used often enough to keep them clean and shiny, so scammer mechanics see those rusty rotors and decide that they can get a lot more money from you. That's why before you take your car in it's wise to put the car in neutral to disable regenerative braking and do a long hard brake on a freeway off ramp or down a mountain pass and that will make your rotors clean and shiny again and the scammer won't be able to make BS claims that rarely used brake rotors are down to 30%.
     
  5. sam spade 2

    sam spade 2 Senior Member

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    THIS.
    That situation is possible but HIGHLY unlikely.
     
  6. bisco

    bisco cookie crumbler

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    never trust your safety to conspiracy theories
     
  7. sam spade 2

    sam spade 2 Senior Member

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    Not a theory.
    It is a FACT that many shops blindly replace rotors and maybe even calipers along with the pads, without even giving them a good inspection. And a LOT of people fall for it.

    And then I had this thought last night:
    What IF the "service advisor" or "mechanic" didn't know the difference between the pads and rotors.......and really meant that the pads were worn out ????
    Or maybe the owner mis-understood.

    A bit of a stretch maybe but not impossible.
     
  8. bisco

    bisco cookie crumbler

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    true, but it is a theory that the o/p's rotor is fine, which should be proved or disproved by a second opinion
     
  9. mr_guy_mann

    mr_guy_mann Senior Member

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    As disc brakes get used the pads are pressed against both sides of the rotor. The resulting friction of the pads rubbing against the rotor converts mechanical energy of the spinning wheels into heat energy. The part of the rotor where the pads rub is called the "swept area". Since the rotor is made of cast iron, the swept areas will tend to rust if exposed to water and salt. On most cars normal day to day use will usually scrub off light rust formations and keep the swept areas clean and the brakes fully functional.

    What can happen is heavy rust can form on the swept areas - esp on cars that get little use of the brakes (like a prius) and more so in locations with more salt or road brine use. Heavy rust won't "self clean" from the rotor, and will creep across most of the swept area as time goes on. That reduces the friction brake's ability to work properly- since rust ain't a very good friction surface. IMG_20210720_170027027_11.jpeg
    This was a car I saw last week(not a prius)- still had 6mm on the pads but the front rotors are garbage. Rear brakes were fine. Under normal braking you aren't likely to notice if your rotors are in good condition or not, as regen does alot of the "work", and the electronic braking system sits between your foot and the rotors. Short form, get a second opinion of your brakes.
    PS. The rotors were trashed on my Gen2 when I got it, and shortly after replacing them I had to routinely shift to neutral and do long brake applies (as recommended by Priuscamper) to keep my rotors "clean".
    Those who live in drier / low salt enviroments don't have these problems.

    Posted via the PriusChat mobile app.
     
    #9 mr_guy_mann, Jul 24, 2021
    Last edited: Jul 24, 2021
  10. Mendel Leisk

    Mendel Leisk Sand Pounder

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    Why am I thinking of this?

    upload_2021-7-26_13-50-48.png
     
  11. Danny13pruisc3

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    You probably should avoid going to the dealer and shop around for a smaller independent shop owner.
    He probably meant to say brake pad instead of rotor.. and since its' a prius hardly using the pads.. you can probably go years before needing to replace the pads. I wouldn't even waste my time going to get a second opinion since most of the braking is regenerative.
    How many miles are on the car? If you ever get a flat tire have a peek at the pads then while you're there.

    btw I bought a gen 2 with 320k miles.. they had the brakes changed at some point and were in the back.. and they looked to be 25 to 30% still there..
     
  12. sam spade 2

    sam spade 2 Senior Member

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    Sorry but that is BAD advice.
    Brake components can go bad at any time for a variety of reasons.
    IGNORING a report like he got is just not a wise thing to do.
     
  13. Colorado Boo

    Colorado Boo Member

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    While brakes are in the category of "if it ain't broke don't fix it" you do want to get a 2nd opinion due to the age. If either the rotor or pads need replacing, just go ahead and spend the extra to get both replaced....will last for years and years on a hybrid. You are in Canada so might have some rust on there which would degrade them.
     
  14. Danny13pruisc3

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    It wasn't advice. I didn't advise him to do it. I said what I would do. It's not like the brakes are going to fail because "the rotor is at 30%" LOL or even if the pads are at 30%... They'll last for years. No need to go out of your way to get a second opinion. it's not like a dangerous situation was reported..
     
  15. ChapmanF

    ChapmanF Senior Member

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    By the same token, if it won't brake, do fix it.
     
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  16. Danny13pruisc3

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    I just reviewed the ad where i bought my gen2. seller said they were changed 5k miles ago..
    These things look to be about 30% left.. I have to wonder if they were the originals.. and I have to wonder if
    the previous owner "was advised to change them" there is plenty of meat left on them and I would have waited..
    of course it's possible that the brakes were changed once before (or more) so no you don't need to reply saying that.
     
  17. Danny13pruisc3

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    Back to the original post.. I've never heard of a rotor going down to 30% and not the brake pads. I would say it's probably impossible. It doesn't make sense. I've heard of rotors warping due to heat and icy/cold conditions.. but that would take out the brake pads with it. you would likely feel pulsations and know they were warped. I'm pretty confident someone meant to say pads..
     
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  18. sam spade 2

    sam spade 2 Senior Member

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    There absolutely is implied "advice" any time you say "This is what I would do."
     
  19. Mendel Leisk

    Mendel Leisk Sand Pounder

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    This expression “30 percent”: with disk brake pads, new thickness is around 10 mm, and “service limit” usually pegged at 1 mm. So aforementioned percent is roughly 3.5 mm? Trust me, if you’ve gone to the trouble involved, have pads in your hands with just over 3 mm (1/8”) remaining friction material, likely with edges flaking away, you’re gonna be loath to put them back into service.
     
  20. vvillovv

    vvillovv Senior Member

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    Usually fairly easy to check how much rust is on a rotor with a quick visual, even if having to remove a wheel. Especially if the rotor is 70% rusted. ;)
    @Species5618w like Bisco s take above. Case closed :p
     
    #20 vvillovv, Sep 15, 2021
    Last edited: Sep 15, 2021
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