Very hot rear discs after pad replacement

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by dave gilmour, Oct 21, 2021.

  1. dave gilmour

    dave gilmour Junior Member

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    Hi there, as per title I paid local garage to replace rear pads on my gen3 and as I have previously had experience of one caliper staying on with stuck sliding pins I now check after each brake job.

    Before the new pads after a short drive the front and rear discs were only very slightly warm to the touch. Now the fronts are still that way but the rears are very hot and I wonder if they didn't seat the new pads properly and if they are rubbing constantly.

    Only had the pads on for 2 days and maybe 10 miles of driving, do you think this will fix itself with the pads getting an initial wearing? Is this maybe "polymerisation"?

    Posted via the PriusChat mobile app.
     
  2. burebista

    burebista Member

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    Hope they put the pistons in X position
    [​IMG]
     
  3. dave gilmour

    dave gilmour Junior Member

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  4. dave gilmour

    dave gilmour Junior Member

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    I haven't noticed a drop in MPG, if the pistons were not aligned would that be a drastic drop in MPG?

    Posted via the PriusChat mobile app.
     
  5. Nor'easter

    Nor'easter Member

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    The Prius is supposed to have a very low drag friction brake system. Your shop butched it up (there are a couple of ways that can happen on rear brakes). Take it back, they should fix it correctly.
     
  6. ASRDogman

    ASRDogman Senior Member

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    They won't fix themselves.
    If they only replaced the pads, and didn't clean and relube the pins, that could be your problem.
    Also, if they didn't align the pins and pads correctly, they can also cause a problem.
    As stated, return to the place and have them check it out and do the job correctly, if they didn't.
    Show them the caliper/pin layout in post #2.

    And if they won't, stop payment on your credit card for the fake repair.
    Then take the car to a place that will do it correctly.

     
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  7. Mendel Leisk

    Mendel Leisk Sand Pounder

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    Yeah, per @burebista's picture in post 2, when reassembling rear brakes the brake caliper piston has to be oriented like an "X". There is a stubby pin on the pad backing plate, that must be positioned between two of the raised spokes in the piston face pattern. When positioned thus it prevents the piston from rotating when the parking brake is applied.

    If the piston is misaligned, so that a spoke in that piston face pattern rides up on the pin, then you're going to get grossly uneven brake pressure, and constant drag. To avoid that:

    1. First off, before doing any brake diassembly, it's a VERY good idea to disconnect and isolate the 12 volt neg cable.

    2. When reassembling rear brake calipers, ensure the piston face looks like this:

    upload_2021-10-21_7-30-20.png
    (The shaded areas are the raised spokes)

    3. Reassemble brakes with piston oriented thus, pump brake pedal several times, and then reconnect 12 volt neg cable. (The brake pedal pumping before reconnection of the battery ensures the car doesn't detect any excessive brake pedal travel, throw a code.) Do NOT apply the parking brake yet.

    4. Take the car for a short (say round-the-block) test drive. Go gentle on the brake.

    5. To check everything's ok, when you get back, apply/release the parking brake several times. Then chock the front wheels, raise the rear of the car, and test-spin the wheels, verify they're spinning semi-freely. Being disc brakes there's a slight amount of drag normally, but they should spin 2~3 revolutions with a good push.

    Attached is a Repair Manual excerpt with more brake info, good to pass on to your mechanic. It has the above picture. Also, here's a short video, how the wheels should spin when assembled properly:

     

    Attached Files:

    #7 Mendel Leisk, Oct 21, 2021
    Last edited: Oct 21, 2021
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  8. Paladain55

    Paladain55 New Member

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    Yup. The sliding pins would be why. The rotation of the rear piston could be an issue too. Block a front wheel, jack up the rear wheel, and spin it by hand. Compare it to the front. If it is worse take the wheel off, the caliper off, and spin the hex head of the sliding pins with a wrench and see if they are free. More than likely the sliding pins are frozen and could need grease.
     
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  9. dave gilmour

    dave gilmour Junior Member

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    Thanks for all the info guys! I took a few videos of my rear wheels spinning and my UK offside rear looks OK while my nearside rear seems to be sticking.

    Wheat do you think?

    Nearside:


    Offside:


    Posted via the PriusChat mobile app.
     
  10. Nor'easter

    Nor'easter Member

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    That's not horrible... but it's not correct. Sticky pins, sticky e-brake mechanism, sticky cable, more rarely (but easier to miss in routine pad replacement): failing hose at the caliper. It -might- improve a bit in a couple hundred miles of normal service, but I would not expect it to revert to normal.
     
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  11. Mendel Leisk

    Mendel Leisk Sand Pounder

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    Yeah rear/right has too much drag. Think they should check both sides though, just to be sure.

    This brake style (pin on backing plate locking against caliper piston) is not uncommon, still a significant “tripping hazard” for brake mechanics not accustomed to it.

    Considering one side is ok, the other not:

    Your mechanic may know the drill, about aligning the piston and so on, but still didn't get it right, because after assembly, and before ever applying the parking brake, you want to press the brake pedal multiple times, with the aim of eliminating excessive brake pedal travel, and it gets all the brake components well seated.

    Really: a thorough brake job should include a subsequent test-drive and post-drive spin test. There's various things that can go wrong, and conscientious mechanic will check for them.
     
    #11 Mendel Leisk, Oct 21, 2021
    Last edited: Oct 21, 2021
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  12. rjparker

    rjparker Senior Member

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    Another issue that could have happened is the brake booster activating with the calipers off the rotor.
     
  13. Colorado Boo

    Colorado Boo Member

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    Dang don't you just hate when mechanics don't do it right? Even when I get my oil changed at the dealership, I don't go anywhere until I pop the hood and just do a quick check of the oil level....trust but verify!
    Show the folks that video and they should offer to make it right. (For future jobs, learn to do it yourself...it's really not that hard and lots of us in here can help!)
     
  14. OptimusPriustus

    OptimusPriustus Junior Member

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    Local garage mean it’s not dealership? They may have used cheap pads that need hammer to get into brackets. I often use file to get decent fit altough i nowadays use oem stuff as often as possible. And it’s not bad idea to replace brackets in old cars. They’re cheap
     
  15. dave gilmour

    dave gilmour Junior Member

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  16. OptimusPriustus

    OptimusPriustus Junior Member

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    Never heard of such brand. But they may still be good.

    Honestly, if wheels turned that way after DIY brake job and only 10 miles driving i’d leave it be. Follow up for a while. That is IF parking brake and brakes in general feel and work normal. When the drag start really influencing MPG you’ll smell it and then the disc shall be truly hot.
     
  17. Mendel Leisk

    Mendel Leisk Sand Pounder

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    If it is a case of the spoke riding up on a pin, this is what it'll look like after a while:

    upload_2021-10-21_13-15-32.png
    upload_2021-10-21_13-16-17.png
    (inside face of rotor)
    upload_2021-10-21_13-17-22.png
     
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  18. Colorado Boo

    Colorado Boo Member

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    Well pads and rotors USED to be cheap, not anymore! I just did a front pad/rotor replacement on my daughter's 2012 Sienna and spent $288 and that's with my military (veteran) discount! I've had good results from the Bosch rotors and the Import Direct pads from O'Reillys...never any problems. I called the Toyota dealership for my daughter to get brake prices and they said it's $320 for pads and to turn the rotors. I asked how much with new rotors and they said it's just over $500....holy moly, Batman!
     
  19. Mendel Leisk

    Mendel Leisk Sand Pounder

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    Front Brake pads at McGeorge Toyota, for 2021 Prime, are $61.73 USD (plus shipping). Not clear if they come with replacement shim set.

    https://toyotaparts.mcgeorgetoyota.com/v-2021-toyota-prius-prime--le--1-8l-l4-electric-gas/brakes--front-brakes

    Rear pads are $39.68:

    https://toyotaparts.mcgeorgetoyota.com/v-2021-toyota-prius-prime--le--1-8l-l4-electric-gas/brakes--rear-brakes

    I would never even entertain using an alternate manufacturer, just not worth the potential hassles.
     
  20. Colorado Boo

    Colorado Boo Member

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    Yeah, I do prefer OEM parts for most things but brakes and rotors aren't on that list because they are pretty basic..no electronics or anything. I don't even want to buy an aftermarket 12-volt battery for my wife's Prius which should be needing one this year or next on the 2017.
     
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