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Grinding and cracking from the rear

Discussion in 'Gen 3 Prius Technical Discussion' started by AnnaKitten, Nov 21, 2017.

  1. AnnaKitten

    AnnaKitten New Member

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    2010 Prius
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    Five
    I bought my Prius a few months ago and have had no major issues with it so far. It drives like new even though it has 182000 miles on it. That being said:
    Last month I noticed a very faint grinding sound coming from my wheels. I am not 100% sure if front or back but it isn’t too noticeable unless you have the windows open and drive slow. My car has also been getting increasingly louder on the freeway. (Not engine sound). I figured it might be the wheel bearings and had them both replaced 2 weeks ago (only in the rear). Ever since that happened though my car has been grinding and cracking in the back whenever I brake. It’s mainly when going uphill and rolling to a stop or lightly braking.
    The strange thing is, as soon as I drive about 3 miles and the car starts to warm up the grinding stops entirely.
    Does anyone have suggestions on what it could be? The brakes are in good recondition and are not worn. And my tires are also in good condition. The car has had regular maintenance as well
     
  2. bisco

    bisco cookie crumbler

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    welcome!
    could it be rust on your rotors?
     
  3. Mendel Leisk

    Mendel Leisk Senior Member

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    Replacing rear bearings means the calipers and rotors also came off. Maybe something messed up when reassembling? There is one gotcha I can think of. Was it a Toyota dealership shop?
     
  4. AnnaKitten

    AnnaKitten New Member

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    I did the bearings at home but it wasn’t my first time doing it. It could be that the dust shield in the back is bent. But it’s strange that the car only makes the cracking sound when it’s cold.
     

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  5. Mendel Leisk

    Mendel Leisk Senior Member

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    Have you done rear disc brake Prius before (3rd gen onward)? It's important to get the caliper piston pattern looking like this:

    upload_2017-11-22_7-52-59.png

    More than "HINT", the above is necessity, to avoid rear brake drag. There's a stubby pin on the backing plate of the brake pad in contact with the piston. It must fall in between the raised spokes, in a hollow. The piston will try to rotate whenever you apply parking brake, the pin is there to prevent this.

    If it's not well seated between the spokes, the piston will rotate, screwing outwards, which will cause dragging brakes, both because the piston is too extended, like the parking brake's always partially on, and because the pin rides up on a spoke, skewing the pad, creating uneven pressure on the rotor.

    You can do quick check by raising the rear and spinning the wheels: a good push and they should go a revolution or two. There's a little drag always, but it should be minor.

    If they're badly dragging, pull off the caliper* again, check condition of inner pad, if it's wear is even, edge-to-edge. Also check the inside face of rotor: is it uniformly shiny: a rusty zone will indicate uneven pressure as described above.

    The key to avoiding this condition is to first ensure the pin is between the spokes at reassembly, then pumping the brake pedal multiple times, getting the caliper piston well seated against the pad, then reconnect 12 volt, then maybe a short test drive and subsequent check of how freely the wheel spins. Only then use parking brake.

    *Disconnect 12 volt battery negative cable first, to avoid possibility of brakes pressurizing and pushing out piston.
     

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  6. Mendel Leisk

    Mendel Leisk Senior Member

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    I'd be interested to know: how did it go taking the rear wheel bearings off, what technique/tools.
     
  7. AnnaKitten

    AnnaKitten New Member

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    Well it was my father and my boyfriend who did it, since they were the ones that had done it on a couple different cars before. The bearings were very rusty and they had to use a lot of force to break them free. They managed to do it on both sides and said the rotors were still in good condition. I will be checking the dust shield tomorrow to make sure it isn’t bent. And I will have them check the brakes again to make sure they followed the steps in the manual
     
    CR94 and Mendel Leisk like this.