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Help! Brake pistons - how to retract??

Discussion in 'Prius c Care, Maintenance and Troubleshooting' started by Kingsway, Aug 11, 2018.

  1. Kingsway

    Kingsway Active Member

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    I'm getting desperate and stand to lose a days work tomorrow if I can't get the car back together!!


    The job seemed to go so well, until I tried to refit the rear brake pads. I can turn the piston 'till the cows come home, and they will NOT retract!!

    If I apply the parking brake, the pistons ratchet out, just as they should. But I can find no way to make them go back in again.... I have disconnected the brake cable - but is there something else required in order to retract the pistons???


    I'd be so grateful for any help!!!
     
    #1 Kingsway, Aug 11, 2018
  2. Mendel Leisk

    Mendel Leisk Senior Member

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    What are you using to turn them? One of these?

    upload_2018-8-11_10-24-44.png

    FWIW, you should be able to screw it in even with needlenose pliers tips.

    Were you applying the parking brake while the caliper was off the rotor? This has me wondering if the piston has come out too far. Can you post a picture?
     
    #2 Mendel Leisk, Aug 11, 2018
  3. PriusCamper

    PriusCamper Senior Member

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    Did you remember to disconnect the 12volt so you aren't working on the braking system when it's still live?
     
    #3 PriusCamper, Aug 11, 2018
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  4. Kingsway

    Kingsway Active Member

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    I just could not put enough pressure on the end of the piston... The tool I bought did not fit properly - but I could wangle it so that it pushed against the piston, and hen I turned the piston with a pair of pipe grips! Once started, it was a lot easier and I could use just the needle-nose pliers and hand pressure. I found the following...

    QUOTE
    The adjuster inside is threaded, as the piston moves out the adjuster turns. To 'unadjust', as you can't reach the adjuster, you turn the piston. The pressure the tool puts on the caliper holds the threaded adjuster still allowing the caliper to wind around it and go back into the caliper body.
    Have a look below at a typical rear caliper:
    UNQUOTE


    https://www.2carpros.com/forum/automotive_pictures/62217_cal2_1.jpg
     
    #4 Kingsway, Aug 12, 2018
    Last edited: Aug 12, 2018
  5. Mendel Leisk

    Mendel Leisk Senior Member

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    Sounds like the regular 3rd gen Prius rear brake, the North American version at least. Odd that it won't screw in. FWIW I'll attach 3rd gen brake info from Repair Manual; I'm not sure how similar it is, but might help.

    Do note: it's imperative to have the piston oriented with the spokes looking like and "X", so that the stubby pin on back of inner brake pad is in between spokes, firmly seated thus. This prevents the piston from rotating when the parking brake is applied. If the piston does manage to rotate, a spoke can end up atop that pin, causing uneven brake application, drag, rusty zone on the disc (due to lack of contact).
     

    Attached Files:

    #5 Mendel Leisk, Aug 12, 2018
  6. Kingsway

    Kingsway Active Member

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    Oh well - I'll know how to do it next time. Ironically, it is a very simple caliper and pad arrangement, which should be very easy indeed to work on - as log as you have the right tool/know-how to wind the piston back!
     
    #6 Kingsway, Aug 12, 2018
  7. Kingsway

    Kingsway Active Member

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    I looked very carefully for the a pin on the piston and corresponding indentation of the pads - but it simply isn't there on this car. They appear to rely on friction to keep the adjustment from winding back - and It was only when I was able to put a LOT of pressure on the end of the piston, that it became possible to adjust it....
     
    #7 Kingsway, Aug 12, 2018
  8. Mendel Leisk

    Mendel Leisk Senior Member

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    It's a pin on the pack of the pad, and it nestles between the spokes on the piston. Or it should: that's why the piston orientation needs to be "X" oriented, like this:

    upload_2018-8-12_10-49-35.png

    (Screen grab from the attachment I posted. Again, this is 3rd gen, not c, so not sure how relevant.)

    And this is the pin. It's stubby, but it's instrumental in keeping the piston from rotating when you apply the parking brake, and it must be locked between the piston spokes to do this:

    upload_2018-8-12_10-54-16.png
     
    #8 Mendel Leisk, Aug 12, 2018
    Last edited: Aug 12, 2018
    Matt H and Raytheeagle like this.
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