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Hum (rear end)

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Jimi1976, Aug 11, 2015.

  1. Jimi1976

    Jimi1976 Active Member

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    2010 Prius
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    III
    My 2010 is humming like bad.....I think it's the rear. the faster you go, the louder it is. Put new tires on - same noise.

    I've lost almost 10 MPG.

    Dealer checked bearings - said they're fine. Tech used stethoscope. He did hear the noise during test drive, but couldn't locate the source, and I couldn't sit at the dealer any longer without going mad.

    anyway - anybody have a clue? I'm thinking about doing the rear bearings anyway....
     
    #1 Jimi1976, Aug 11, 2015
  2. xliderider

    xliderider Senior Member

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    The brake pads could be dragging in the rear. After driving around, carefully feel the rear rotors on both sides of the car to see if they are hot from the friction of dragging brake pads.
     
    #2 xliderider, Aug 11, 2015
    Mendel Leisk likes this.
  3. frodoz737

    frodoz737 Top Wrench

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    Get it properly diagnosed. If you can't sit around the Dealership all day (or where ever), rent a car.
     
    #3 frodoz737, Aug 11, 2015
  4. Jimi1976

    Jimi1976 Active Member

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    III
    Autonation Toyota in Centennial, CO looked at the car - heard the noise, found no issue.
    This weekend - I grabbed a new hub, and popped the wheel off (with a good friend, who is a much better mechanic than I am).
    anyway, the second we started pulling the brake caliper off.....we realized it was a dragging brake pad (inner pad, driver side rear).
    The lower slide pin was locked up....and needed some torch time to break loose (otherwise, I was staring down a new caliper assembly....which aint cheap!). Got the pin broke free....the rubber boot at the end was gone, and the pin was pretty rusty. All of metro denver (including 2 toyota dealers) do not stock caliper pins. Go figure.....dealer couldn't figure this out?

    anyway - soaked the pin in PB, sandpaper to it and the pin cylinder......and the pin is sliding nicely now.
    I will order a new pin (and boot....since the heat did a little damage to it). So......all that heat and noise was in fact from a dragging brake (as xliderider suggested).

    also worth noting......the little expansion springs (to retract pads off rotor) were non-existent. they're installed now, though!
     
    #4 Jimi1976, Oct 11, 2015
  5. frodoz737

    frodoz737 Top Wrench

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    Good find. Might be a good idea to clean and lube the rest of the pins (F&B)...if you haven't already.
     
    #5 frodoz737, Oct 12, 2015
  6. Mendel Leisk

    Mendel Leisk Senior Member

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    Check that your rear wheels are turning freely now. Make really sure the caliper piston is oriented so that the pin on back of pad lands in between the spokes on piston face. Further: after re-assembly, depress the brake pedal repeatedly, make really sure the piston is bedded against that pad. Even take it it for a short drive, lots of easy brake applications.

    Only then should you apply the parking brake: if you just assemble the rear brake, and then apply the parking brake, there's a decent chance the piston will rotate and ride one of the piston spokes up onto the pad pin, skewing everything, and creating a lot of drag.
     
    #6 Mendel Leisk, Oct 12, 2015
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