2012 Prius - New Calipers, Pads Still Dragging (hot brake discs)

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by andreimontreal, Nov 17, 2019.

  1. ASRDogman

    ASRDogman Senior Member

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    MAYBE, because they will swell when they get hot, because the fluid gets hot, quick!
    And might slowly release pressure as they cool down.

    Mine did that on a Probe I had. I didn't think I needed them. But they were inexpensive, so I bought them.
    The brakes were fine after that.
    Maybe the brake accumulator is bad and supplying constant pressure? The rears are electrically controled.
    But they function the same way the fronts do. If you rebuilt them, and honed/cleaned the cylinder super good,
    they piston should function smoothly

    I don't care for "rebuilt" calipers. I prefer new. Less likely you'll have problems. But I have rebuilt mine before, without
    any problems.


     
  2. andreimontreal

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    No the pressure is constant - I even hear a grinding noise lately from the scraping. I checked with Techstream the pressure/valves function - all seems good; see a few posts before around #88 ottomh.

    My old Tokicos are so rusted I couldn't make anything out of them. The current ones are Raybestos - renamed Chinese crap in my books lately. So, yeah, sounds like new Tokicos are about my only sound option.
     
  3. ASRDogman

    ASRDogman Senior Member

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    Okay, well, I'd try the rubber hoses. Inexpensive, easy to change.
    If that doesn't work. Invest the money and get better calipers....
    You've invested a lot of time, and headaches....
     
  4. ChapmanF

    ChapmanF Senior Member

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    If there are already dad-hoarded instruments around that could be used to test these Raybestos parts, that ends up being free, and kind of fun, and will lead to the satisfaction of knowing something (one way or the other) about what is going on.
     
  5. andreimontreal

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    @ChapmanF

    I def have fun with stuff like this (minus the pain of having to rely on the car which is stressing) and I don't want to badmouth Raybestos for nothing - so I really want to get down to the problem.

    Piston travel - 0.34-0.35 mm . The first measurement when it jumps 0 to 5 it adjusts (I did it several times different clamping, various positions, got the same results). So based on your caliper old posts the caliper works great.

    Axial deflection - 0.08mm - is that bad or good? Heat might've warped the disc - look at it: so black and bumpy.

    Free spin test - no pads, no caliper on ... all seems smooth, quiet and good, when I filmed the car decided to make noise.

    (@ASRDogman ) And then - seeing these measurements I thought maybe I'm wrong about that hose - I bled the brakes, so with engine running, I depressed the brakes, and bled them again and it still dripped (see 4 and 40 seconds in , sorry for the vertical) - it shouldn't drip like that, right? Just to make extra sure you're all talking about changing hose/part 47316A - right?

    EDIT: Looks like I have a rear outer brake hose from Raybestos - well ... back to work tomorrow.
     
    #105 andreimontreal, Aug 19, 2020
    Last edited: Aug 20, 2020
  6. ASRDogman

    ASRDogman Senior Member

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    I would say that is the hose. (Toyota) It attaches to the caliper and the steel tube.
    You could get an aftermarket hose. It "should" be okay.....
    Gravity will allow the fluid to continue to leak.

     
  7. ChapmanF

    ChapmanF Senior Member

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    The numbers look good and the video is great, only I was not able to see the rest of your setup, how you were actuating the caliper—that was outside the right edge of the frame. (I should mention here that maybe you explained it verbally; for boring technical reasons, a lot of my youtube viewing happens in silence.)

    My most convincing results were when I was testing the caliper out of the car, using only gentle puffs from an air hose in the back nudging the piston out to just kiss some hard blocks in place of the rotor and pads, then watching the return when the air was released.

    My least convincing results were one time when I tried the test on the car, using the brake hydraulics to move the piston. Even being 'gentle', the hydraulics are powerful enough that I was really measuring the stretch and return of the caliper body.

    As long as your technique was free of that issue, I would say those numbers get the caliper off the hook.
     
  8. andreimontreal

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    Basically, I looked at your bench test and figure how I can do the same.

    If I understand you correctly, yes I accounted for that. I unhinged the caliper and lifted it 1cm or so. About 75-80%% of the piston would clamp the pads/disc and the caliper wasn't attached to the pins/bracket but just free floating staying on the pads through friction. The dial's pin was placed vertically onto the piston as seen through the caliper's body and the dial's bracket was screwed onto a 2x3 pine and clamped with a Bessey screw clamp onto the actual caliper as to get a "1 piece" type of system. Pulling the dial's bracket it couldn't move - it was solidly anchored so there was no room for error.
     
  9. andreimontreal

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    Yeah, already had one of those since from day 1 I heard mentions of an issue like that. I've been trying to open it. It seems like the bolt on Brake line 4 is seized. I tried WD-40 and a flared wrench - won't budge. I tried rotating the flexible hose while holding the nut on line 4 and the line started to bend. It is quite rusty there for 10-15cm. I think I need to replace that too given how FUBAR the situation got - the only thing which pissed me off is that I have to wait :D.

    EDIT: Somebody was talking about how they flared and installed non corrosive tubing on their Prius. I wish I had those tools right now. Looks like it takes some specialized tools which seem to cost more than I care to spend.
     
    #109 andreimontreal, Aug 20, 2020
    Last edited: Aug 20, 2020
  10. ChapmanF

    ChapmanF Senior Member

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    I am a recent convert to, and therefore that annoying guy who won't stop talking about, Lisle's 62140 "seized fastener removal" kit. It doesn't try to twist anything, it just bops away on the fastener straight end-on, while you gently twist, and is astonishingly effective, with much-reduced risk of breaking something off. One of those "where were you all my life?" tools.

    I don't remember what I spent on a basic set of flare tools back when I first bought 'em, but I don't remember it was that much. I was driving this sort of mongrel Ford thing at the time, Canadian body, German engine, Japanese transmission, US transfer case. Frustrating about the brake lines was they used standard diameter tubing, but would use different diameter flare nuts on different lines to reduce assembly errors, so pre-flared generic replacements never came with the right ones, and I had stacks of adapters that looked really bush-league, and got tired of it. It was so much more satisfying to start with a coil of tube and make the thing I needed, with the right ends on it.

    Later on, I discovered the CuNiFe tubing, which not only resists rust, but is softer and way nicer to bend by hand than steel tube.

    I'm still curious what was moving the piston in your video though. Gentle puffs of compressed air, or ... ?

    Under hydraulic braking forces, the caliper itself stretches and reshrinks. The pads squish and unsquish. These are not materials that seem elastic under human-scale forces, but under bigger forces they are, easily enough to see on a dial indicator.
     
    Mendel Leisk likes this.
  11. ASRDogman

    ASRDogman Senior Member

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    Having the right tool is invaluable! That's why I 10's of thousand of dollars worth of them.
    I should sell them all and just stay home!

    I don't know if you have a harbor freight but they may have some inexpensive ones.
    Sometimes you can use heat from a small torch, but it's touchy with brake fluid.

    WD-40 is not a great rust penetrant. I would get some though. And spray and let it soak,
    then repeat, and repeat, and repeat...
    You can always get a repair kit so you can slice into the line. NOT the best way to do it, but....

     
  12. andreimontreal

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    Oh, yes, somebody was depressing the brake pedal on my signal.

    I meant the pipe nut on the metallic brake line - a kit like that wouldn't work. That line is so so rusty near the hose connection. I tried to hold the nut and to rotate from the hose end and it started bending the brake line badly - WD40 applied several times in 30-40min.

    I even used a 10mm flare wrench from Can Tire and it damaged the nut a bit. Not sure of it's the wrench that is bad or what. Down the line the other nut seems to be slightly better. Gonna look for an exchange part since it's fairly inexpensive, a better flare wrench and a blow torch and try again soon.

    You think I should DYI this? Doesn't look hard at all but. If I can find that piece fast and cheap I won't sweat it for now. Although I'd like to be in a position where I can do my own thing from scratch. I have to look for the tools, piping, those 10mm tapered nuts - too much work and I have a host of things to do.
     
  13. andreimontreal

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    Yeah, I'm a potential future tool addict too - and quality tool addict while at it.

    We have Princess Auto in Canada - never used it but was browsing and I did find brake pipe kits. Some mechanics on youtube use blowtorches indeed - I'm thinking about doing that - better that than not being able to remove something. Speaking of penetrates, Project Farm has a comparison test - and Liquid Wrench seems to have a slight edge over the rest but couldn't find it in store.
     
  14. andreimontreal

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    Actually I found this clip for flaring/bending pipe and the tools seem simpler - that would be useful for the compressor and whatnot.

    Since you mentin cunifer piping I think it was you who told me about it before @ChapmanF . Sounds very familir.

    EDIT: Seems that NAPA has a lot of brake line options and tube/nut kits. As much as I love the idea - I'll check with Toyota to see if I can get the part cheaply first. Found Eric Car Guy's kit - not bad price wise, not sure I wanna spend now. Cheaper kit.

    @ChapmanF and @ASRDogman : Something I don't fully grasp: why is the piston moving properly in the test if the line would not be working well? If the line was broken, shouldn't I see the piston not retract as well?
     
    #114 andreimontreal, Aug 20, 2020
    Last edited: Aug 20, 2020
  15. ChapmanF

    ChapmanF Senior Member

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    Ah. I think I'd be a bit less confident of the result then. The most convincing results I got were with the caliper on the bench, blocks in the jaws, just puffing air from the end of an air hose in through the brake line hole in the back. Just enough force to slip the piston out to kiss the blocks, then see where it returns to after the puff.

    No brake pedal, no hydraulic pressure, no stretching the caliper or squishing the blocks ... those effects exaggerate the movement seen on the dial indicator,
     
  16. andreimontreal

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    Are you saying the caliper can actually bend under those forces? Not entirely surprised as first I put in one of those tools that pushes the piston and it started to bend it so I stopped. And it's made of at least 1/4" steel.

    How did you do the air fitting connections and how much PSI did you pass through?

    I'm so weary of trying to get the caliper full of brake fluid out - I can't express the UGH that sits in my gut :whistle: .

    Let me ask 1/2 rhetorically. Whaddya think: should I replace that line? Looks kinda rusty: for 20-30 bucks I'd replace it.

    Caliper Question: I saw this mechanic replace a line and said that he's placed the caliper so he wouldn't lose the fluid. He said he doesn't want bubbles in there - but the line was full of air. So what is he talking about? He's getting air in there either way and bleeding is mandatory.
     
    #116 andreimontreal, Aug 20, 2020
    Last edited: Aug 20, 2020
  17. ChapmanF

    ChapmanF Senior Member

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    Yup - that whole big chunka cast metal stretches right out like a spring when the hydraulic force is on it, and springs right back when the force is removed. Metal is, after all, often used to make springs. The caliper "spring" doesn't stretch very much, nor do brake pads squish very much, but it's enough to mess up a measurement looking for 0.3 mm piston return.

    If you look again at that Delphi finite-element model:

    [​IMG]

    ... you see they explicitly had to model both the caliper housing and the pad linings as springs.

    Literally as gently as possible, like no fittings, a blowgun attachment held in my fist, fist cupped over the hole at the back of the caliper. If it's a caliper that's been freshly cleaned up and greased, moving the piston isn't hard.

    Yes, you should just put the caliper on, don't fuss about the air till it's on, then bleed it.

    That's also how you tell the right and left calipers apart (in case you forgot which part number is which). Look at the angle how they sit on the knuckle. Each caliper is on its proper side when, at that angle, the bleed screw is at the highest point of its cylinder.
     
  18. andreimontreal

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    Exactly - the bleed screw can't be misplaced and it's at the top.

    I could see it too: if the piston bends 1/4" steel like nothing, for sure 0.2mm bending in the caliper is nothing. I have that generic dust blower nozzle with rubber on its tip. RockAuto will send replacements under warranty and I'll check out stuff when that happens in a few days. And I'll deal with the line too just to be safe - it's long overdue.
     
  19. andreimontreal

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    Nope, not the line; still getting hot. Waiting for the exchange calipers.

    It took Liquid Wrench, a propane torch and a Milwaukee proper vise-grip - I had to change both line 4 (solid before the flex) and the flexible line; the nuts were so jammed. I had fun.

    Now that I saw what it means to change a line I might be ready to do a cunifer line exchange in the future. I have this idea that I want to hoist the car up, sand well (maybe with sand+compressor) and then paint some por-15 under the car.
     
  20. andreimontreal

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    Replaced the left caliper with a new one. Just the caliper, kept the bracket for now. Pins sliding well, pads sliding easily, caliper piston seated properly on the brake pad (touching the brake pad), bled the brake with invalid mode till I saw no more bubbles. I scarified a black goat and rolled on the floor 5 minutes.

    Still overheats. Should I ramp it off a cliff already?

    Somebody mentioned that, if the bearing is bad, its heat could be transmitted outwards. The bearing felt quite smooth. Shouldn't a bad bearing feel bad like on a skateboard or roller-blades? I replaced the flexible and hard line right before the caliper. Not sure what else to do to it.

    I'll repeat this little detail. When I discovered this issue, the RL caliper's pins were much more damaged compared to RR, badly rusted/pitted and jammed up. Not sure what it means but something is going on at the RL wheel.

    I'm just about ready to go see a mechanic.
     
    #120 andreimontreal, Sep 10, 2020
    Last edited: Sep 10, 2020
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