Brake Rotors heating unevenly?

Discussion in 'Gen 2 Prius Main Forum' started by 20DPT21, Sep 13, 2019.

  1. 20DPT21

    20DPT21 New Member

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    Had my rear brakes replaced 3 weeks ago by my parents mechanic (about 150 miles from my current location) on my 243,000 mile 2006 prius. Three days ago I noticed a slight clicking occuring with every wheel revolution in the drivers side rear wheel well, and after driving home from work 55 miles I inspected the rear wheels and noticed the rotor on the drivers side rear was extremely hot compared to the other tires.

    I brought it in to a local shop to do a diagnosis and hopefully get some answers-- they disassembled the rear brakes and found a loose pin on the drivers side brake foot pad (something like that, don't have paperwork in front of me right now). The noise is no longer present, and there wasn't any heating on the test drive they did or the 10 miles I drove last night. This mechanic said all was ok with the brakes and should be good to drive.

    Today, I drove 55 miles to work and noticed that the drivers side rear rotor was so hot I could not touch my finger on it for longer than 1 second. The rear passengers rotor was quite warm as well, but not too hot to touch.

    Is it normal for rotors to heat unevenly? There was no burning or chemical smell present.
     
  2. Mendel Leisk

    Mendel Leisk Obtuse Angler

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    That doesn't sound right, way too hot. One question though: is this a US spec 2nd gen Prius? I thought they had drum brakes on the rear?
     
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  3. 20DPT21

    20DPT21 New Member

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    Ah yes I mean the rear drum. Sorry am not very mechanically literate. It seems weird.. I am thrown off because the mechanic took it apart and gave it the all clear.
     
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  4. jb in NE

    jb in NE Senior Member

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    Probably very slightly, but not to this extent. If one brake is significantly hotter, then it is likely from friction caused by the brake not releasing. On rear brakes, this can be due to a parking brake not properly releasing.

    Did you use the parking brake between the 10 mile normal drive and this event?
     
    #4 jb in NE, Sep 13, 2019
    Last edited: Sep 13, 2019
  5. PriusCamper

    PriusCamper Senior Member

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    Have you informed you parents what you think of the quality of work of their preferred mechanic yet?
     
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  6. 20DPT21

    20DPT21 New Member

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    Yea I have, we've had nothing but good work from him for 15+ years. He's refunding costs incurred as well from this

    Thanks for the response. If this were the case, would I be feeling a pulling while driving or experience a decrease in MPG? I haven't experienced either of those. Would this be something that they should have seen while disassembling the brakes?
     
    #6 20DPT21, Sep 13, 2019
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  7. PriusCamper

    PriusCamper Senior Member

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    That's an awesome mechanic if they're willing to give a refund on the work...

    And yes their would be a pulling if one brake wasn't sticking more than the other. And anyone who hasn't yet burned their finger touching a mechanically sound brake rotor that was recently used needs to learn that lesson ASAP. Whereas, if you had a sticking break pad or other damage and it was pulling and you touched that rotor for a 1/10 of a second it wouldn't be a simple 1st degree burn, it's be 2nd degree with oozing and swelling.
     
  8. jb in NE

    jb in NE Senior Member

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    You typically won't feel a pull from a lightly dragging rear brake. You may feel a pull with a significantly dragging front brake, since this is on a steering tire.

    If the brake is only dragging slightly, it can get quite hot without affecting mpg significantly. If the brakes were not so hot that they smoked or smelled bad, a disassembly when they are cool may not show any evidence of heating. If the brake gets really hot, it can heat the drum or rotor to such an extent that it discolors the metal, or can permanently damage the brake friction material, or melt the grease in the wheel hub, etc.

    Edit - road car brakes are not designed for continuous heating. Brakes generate heat through friction, and the heat is dissipated to the atmosphere, typically at a much lower rate than generated. When you apply your brakes, they heat up quickly, then you release the brakes and the heat dissipates and the brakes cool off. If you ride your brakes down a long hill, for example, the heat is generated much more quickly than it can dissipate, and temperature builds up to a point where the brakes become ineffective or you boil the brake fluid away and lose your brakes. When you have a brake dragging, the amount of heating is proportional to the amount of drag and the speed of the car.
     
    #8 jb in NE, Sep 13, 2019
    Last edited: Sep 14, 2019
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  9. PriusCamper

    PriusCamper Senior Member

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    And that's why regenerative braking is so smart... Rather than dissipating that braking energy as heat, it stores it as electricity for future use.
     
  10. 20DPT21

    20DPT21 New Member

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    Ended up bring it back to the mechanic, who used an infrared gun and confirmed the temp differences. They tried adjusting the break pads, but that did not yield any results. They said they think it may be the automatic brake adjustor in the rear (?) Does this sound like a reasonable explanation? They are going to investigate further on Monday. I'm a bit skeptical of the place since this was the mechanic that gave the "all clear" three days ago after disassembling the rear brakes
     
  11. jb in NE

    jb in NE Senior Member

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    Most drum brakes do have automatic slack adjusters, so that's not far fetched. When you install new drum brake shoes, you use a tool to manually adjust the slack to get it correct to start. If they overtightened it, it could cause drag.

    One of the Gen 2 experts can confirm if that is the case on that model.
     
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  12. ChapmanF

    ChapmanF Senior Member

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    Yes, there's an adjuster in the rear drum brakes. It ought to be pretty familiar to just about any mechanic though; there are only about two designs for that type of adjuster, and they've both been around about forever.
     
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  13. Mendel Leisk

    Mendel Leisk Obtuse Angler

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    Here's 2nd gen brake info, might shed some light on the auto adjuster, or whatever.
     

    Attached Files:

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  14. 20DPT21

    20DPT21 New Member

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    Awesome, thats very helpful. Thank you
     
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