New brake discs/rotors and pads still squeaking after 1 month and make twanging noises when parking.

Discussion in 'Gen 4 Prius Main Forum' started by The Professor, Dec 3, 2021.

  1. The Professor

    The Professor Senior Member

    Joined:
    Apr 5, 2018
    538
    740
    0
    Location:
    UK
    Vehicle:
    2017 Prius
    Model:
    Excel
    If there's anyone out there that can help with this one, I'm tearing my hair out over this and could use some advice :D

    This is probably following on from the excessive scoring and wear of the all 4 discs/rotors that I mentioned a couple of years ago in this thread: Scoring on brake discs/rotors. | PriusChat

    So I had the front discs and pads replaced about a two months ago, and the rears about a month ago, after 35,000 miles. The fronts were replaced due to the discs being flagged as "replace immediately" on the vehicles annual test (MOT in the UK). The rears were replaced a month later after the outer pad on the left rear wheel had worn down at an angle, and despite a reasonable amount of the pad being present on one edge, it was down the the metal on the other; the pad had become wedge shaped. The metal scraping against the disc scored a deep groove into it during the 6 weeks (long story) it took me to get to a dealership, hence the replacement.

    The fronts have been fine since they were replaced (and in fact worked fine beforehand, they were just badly worn).

    The rears, however, have had further issues. After returning home from the dealership, both rear discs were smoking hot and smelled terrible. The discs were so hot, the alloy rims were hot to touch as well - I'd describe the alloys as being a hot bath temperature 40C/104F maybe.

    I Googled this phenomenon, and sooooo many sites, including threads on this one, said this is "normal" after replacing the discs and pads and that it should resolve after a day or two once they bed in. So I decided to wait and see what happened. I thought this was odd as my front brakes never suffered from heating at all after replacement.

    Indeed, the left rear brake did seem to resolve itself, and was suddenly cold/slightly warm one day after a 15 minute drive, and has been ever since, but the other was still VERY hot. It was so hot that if I licked my finger tip and tapped it on the disk it would hiss.

    So I went back to the dealership, and they said one of the pads had "slipped" and was being constantly applied at an angle. They replaced the pads again and that seems to have solved it. Both discs seem to be visually OK, despite the heat (not warped) and braking seems normal.

    I do find it curious, however, that both my rear brakes have had one of their pads wearing down at an angle - first my original left rear brake, and now my replacement right rear brake. Is this common?

    Anyway, at this stage, none of my brakes heat up. They're, at most, barely warm after a 15 minute drive through the city. They seem to perform fine in terms of stopping and the car staying straight.

    However, the right rear brake (the one that was excessively heating for a few weeks after replacement) still has two weird issues...

    Firstly, it squeaks a LOT when stopping. You have to press the brake pretty hard for it not to squeak. Anything lighter and it squeaks all the way to a stop. This is SO annoying and embarrassing. It sounds like a huge train squealing to a stop (although it's definitely only one wheel).

    Secondly, when I get home and stop the car, if I have the window open and if the engine's off (so I can hear stuff), I can hear a kind of twanging/creaking sound coming from that wheel after the car's stopped as I'm pressing the brake harder. The harder I press the brake, the longer it makes the noise and the higher the pitch gets by the end. If I release the brake and press it again, the noise repeats. I would describe the noise like the sound you would get if you attached an short elastic band to something and tensioned it, then pluck it to make a sound few times a second while simultaneously increasing the tension on it (thus increasing the pitch). The noise starts as you start to apply the brake and stops within maybe 1/2 second of the pedal hitting the floor. I tried to record the sound just now, but it didn't do it so it may be temperature related. It also doesn't seem to do it when you use the left-pedal-parking-brake, but only the normal central brake pedal - although the left brake's ratchet is possibly too loud to allow me to hear the twanging - not sure.

    It should be noted that the calipers were supposedly checked as "probably fine" during the annual test and both visits relating to the rear brakes and that each time a different person worked on the car. Although I was warned that they may need replacing as a way to fix the excessive heating if it continued (which it didn't).

    Does anyone have any thoughts or suggestions on this before I return to the dealership yet again? Or any easy fixes/checks I can do myself with the vehicle on the ground?
     
  2. Mendel Leisk

    Mendel Leisk Sand Pounder

    Joined:
    Oct 17, 2010
    45,972
    32,837
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    Well not exactly "on the ground": if you can raise the rear (or one rear corner at a time, say just with the scissor jack), apply/release the parking brake a few times and then try spinning the wheels. With a good push they should spin 2~3 revolutions before stopping.

    This an excerpt from 4th gen Repair Manual (PDF excerpt attached):

    upload_2021-12-3_12-20-58.png

    Similar to gen 3, it's imperative that the piston be oriented as shown, and well seated thus, or you'll get the symptoms you describe, bevelled pad wear, constant drag and overheating. My guess would be the shop assembled it thus, put everything back together, and called it done. And that seems to be the rub: you want to assemble it thus, don't even think about applying the parking brake, pump the brake pedal multiple times (to get things well seated, take the car for a short test drive, then apply/release the parking brake, raise the rear and VERIFY the wheels are spinning semi-freely.

    Failing to do this, assembled but not well-seated, especially if the parking brakes is applied forcefully, I suspect what happens is the caliper piston manages to rotate, and one of the raised spokes on the piston face rides up on the stubby pin on brake pad backing plate. Then you get the beveled pad wear and drag.

    Here's how they should spin:

     

    Attached Files:

  3. Hamza Masarwa

    Hamza Masarwa New Member

    Joined:
    Mar 21, 2021
    16
    1
    0
    Location:
    Jordan
    Vehicle:
    2016 Prius
    Model:
    Prime Advanced
    Hello
    I need this manual plz. Screenshot_20211204-072750.jpeg

    Posted via the PriusChat mobile app.
     
Loading...