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. andreimontreal

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    Not yet. I'll try some of Chapman's suggestions first.

    They also did the R66 software check on the ECU. It seems to me that fuel consumption might have gone up even a bit more. I still see 8-11L for short distances and 5.6 - 6ish L for highway.
     
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  2. andreimontreal

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    What's the path for that in Techstream? I checked around saw some brake stuff in Main ECU and Chassis. I figured that it's got to be Main ECU -> ABS/VCS/Traction -> Monitor, but it was greyed out.

    My v1.4 cable drops connections, painful to use; I sent it back - will put an order for vxdiag I think.

    I did a longer run yesterday and now rear left and front right brakes get slightly hot... :cautious: ... this and the booster sounds make me think Toyota might've made a sloppy job fixing that booster. Just a hunch for now.
     
  3. ChapmanF

    ChapmanF Senior Member

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    I think I pretty much always start with a Health Check (just force of habit, maybe?), and then select the ABS/VSC/TRAC, and Data List from the options at the left.
     
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  4. andreimontreal

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    Alright. VXDIAG nano on its way. I'm busy and "locked" in my folks house anyway renoing so won't need to be going anywhere for a long time; will get back to those brakes when the gizmo gets here.
     
  5. andreimontreal

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    @ChapmanF Here I am several months later and what you say makes even more sense. I barely got to drive and also didn't want to touch the car much because of the issues.

    Now I finally got to install VXDaig and I run a health-check. I got a Navigation System - U0073; I got no navigation system so prob that's what it's telling me? Other than that no codes.

    I loaded the "Data List" and I just drove around the block and recorded live feed and I don't see any differences between the wheels. Probably too much stopping and accelerating, I'll try to record on a straight road for this one. Will come back later with clips.

     
  6. andreimontreal

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    So I did a Live reading in Teachstream - first seconds is column 1 and 2, then I slide to column 2 and 3 to see the solenoids too.

    The SSC and SCC solenoids are always ON, currents of 0.4 and - respectively - 0.6 V approximately when at rest and more when braking. I'm not 100% sure if that's right - will get to this in a moment. I found a similar post here - see post #7.

    Brake Diagram of 3rd Gen Prius - as far as I understand (I think that's off 2010 New Car Features Manual NCF - scroll down to page 63 of 68).

    Now, reading at the bottom of page 62, right above the brake diagram on page 63, there is a "Fail-Safe" explanation:

    6. FAIL-SAFE
    (a) Brake System
    (1) When the brake actuator stops, the switching solenoid valves SSC and SCC close and the switching solenoid valves SMC and SRC open. Thus, the fluid pressure generated in the hydraulic brake booster by the driver's brake pedal operation is directly supplied to each of the wheel cylinders.
    So does this mean that the SSC and SCC should be OFF when I stop depressing the brakes?

    I'm a bit confused so far. If you look at SMC and SRC, they do briefly open as stated in there - probably as I let go of the brakes and then they shut off - I'd synced cameras probably and there's also a slight delay of half a second to a second maybe - I really don't know as I haven't played with it too much.

     
    #86 andreimontreal, Aug 10, 2020
    Last edited: Aug 10, 2020
  7. ChapmanF

    ChapmanF Senior Member

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    In that diagram, SSC and SCC are drawn as normally-closed valves (power opens them), and SMC and SRC are drawn as normally open (power closes them). They don't exactly bludgeon you with that information, but look for what side of each pintle the spring is drawn on.

    So the idea is for as long as the ECU is on and happy, it supplies power to all of those, which holds SSC and SCC open for normal operation, and SMC and SRC closed, blocking off the fail-safe paths.

    If the ECU ever becomes unhappy, or just plain conks out completely, the power drops to all four of those valves, and they spring back to their normally closed - respectively - open positions, so the fail-safe braking works.

    So those details, at least, do not seem to indicate a problem.

    Edit: it's weird that you'd see SMC/SRC blipping at all though. I wonder if there's any way that could be some kind of Techstream display artifact.
     
    #87 ChapmanF, Aug 10, 2020
    Last edited: Aug 10, 2020
  8. andreimontreal

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    I agree completely. I didn't pay attention to that - for a while I thought I was too dumb to understand the diagram (shame on me).

    Yeah! That was my first understanding. My assumptions/confusion which followed were wrong - your no power/ springs observation (y)(y)(y) really straightened my confusion once I looked at the diagram carefully mapping out the fluid directions juxtaposed with the live readings.

    I think the Fail-Safe happens with the JZB booster failure - right? - it literally felt like old school brakes. And that's why the Toyota rep said the brakes are fine to use.

    No - see the excerpt below on normal brake operation from the manual but let me lay out my reasoning too as the manual does not explain the why. SMC/SRC need to close once SLA ( the main fluid/pressure line) starts (ie braking starts) so pressure can build up at the 4 brake cylinders otherwise the braking fluid would back up through SMC/SRC in the booster and it would be a closed loop (the path of least resistance). Then, when the braking action is finished (no current, spring action), SLA shuts down and SMC/SRC open up to let the calipers' cylinders back up (along with the pads).

    Get this now - the SSC is a pedal stroke simulator and does this: Generates a pedal stroke during braking in accordance with the driver 's pedal effort ( page 1 ) - so it reads a realistic pedal input to have something to compare with as the digital brake compensates (the regenerator braking and so on). I would think that it's good for SSC to be open at all times (provided brake booster works) because the pedal pressure value is the key for kick-staring (and adjusting) the digital braking system.

    The SCC seems to let to let fluid to the front of the brakes. (btw writing and thinking in real time here :coffee::barefoot:o_O:mad::confused::eek: turning into all shades of blue and red - it's been hours of this :ROFLMAO: ) . So SCC seems to balance the front/back relationship so the car would not tip too much forward when braking. If you look at 00:39, it actually opens up more for whatever reason. The NCF manual talks about this front-rear adjustment - I thought I read something not double-checking anymore. I think they did tests and found out 0.6V to be a good starting point overall for opening that valve: that's my assumption.

    Now, if SCC was CLOSED - once braking would stop - then the rear brakes would have no way to let the fluid to SMC to get pressure relief (though there is SRC which the manual seems to say it does the same once braking stops - either way: it doesn't make sense for SCC to close, a free system is safer). So SCC being continuously open, that means that it's doing its job right because the front brakes are the main brakes in any vehicle and they do the bulk of the job. Furthermore, to talk about the rear additional valves, RLR /RRR (called pressure reduction solenoids) - I think those are related to the ABS/VCS system (most likely - given the word reduction - there need to be some quick outlet for those with independent function from the braking solenoids) and let pressure off only under certain conditions (wheel slips, locks etc).

    I found this in the brake manual at page 37:

    (c) Normal Brake Operation (with Regenerative Brake Cooperative Control)

    (1) During normal braking, the switching solenoid valves SSC and SCC open and the switching solenoid valves SMC and SRC close, and thus the fluid pressure circuit from the hydraulic brake booster to each wheel cylinder is individually separated. Each of the wheel cylinder pressures can be increased, retained and decreased by controlling the linear solenoid valves SLA and SLR under the condition.

    They have a rather incomplete/simplistic way of explaining things. And the list goes on with 2 more points which explain dizzying details about how the ABS pressure is derived (that's what I understand at least) - so much fun.

    I was ready to agree from the start but after all this thinking - more than ever - yeah, everything seems to be working right (y)(y)(y)!!! And when I add to this that I changed the sliding pin bushings for RR wheel and it stays COOL relative to the front wheels (switched Raybestos with oem Toyota from the old calipers during winter- RL still has Raybestos rubber on those pins and gets HOT!). Even more so I know that this whole problem comes down to some shitty cheap pieces of rubber with the wrong compound on them. Can you believe it?


    I think it's time to write RockAuto and complain about it. And next time lesson learned - spend a buck and get OEM (I usually don't cheap out like this but reviews were good on the forums). And if you see a kid cheaping out like I did show him my troubles.

    I think this is crystal clear - what do you think?
     
    #88 andreimontreal, Aug 10, 2020
    Last edited: Aug 10, 2020
  9. ChapmanF

    ChapmanF Senior Member

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    I think you're overcomplicating the system. (And yes, I intend to trademark the combination "overcomplicating" and "Prius brakes", so you can't use it in your own stand-up routine.)

    If you look back on page 22, the solenoid valves are in only three categories: linear ones (they can be electrically controlled to open any fraction of their amount, and so modulate the fluid flow), switching ones (they are open or they're closed, and just used to put the system in one configuration or another), and the control solenoids (the paired Hold/Release valves, one pair for each wheel).

    There are only two of the valves that are linear: SLA and SLR. They allow the ECU to smoothly modulate the application and, respectively, release of the fluid pressure overall. The per-wheel hold/release pairs control how much of that pressure gets to each wheel and when to release it. Observe that when any of the four Release valves opens, the fluid returns directly to the reservoir; there is no other valve in its path.

    The four switchers are just there, in my understanding, so there is a normal and a fail-safe operating mode. Any time the brake ECU thinks it is healthy, SSC and SCC are wide open, and SMC and SRC are tight shut. So as you push the pedal, the fluid from the forward master cylinder chamber goes nowhere but the stroke simulator. You get a nice brake feel (SSC is open) and that fluid goes nowhere else (SMC is shut).

    Meanwhile, fluid from the rear/booster chamber of the master cylinder acts only on the pressure sensor. It goes nowhere else (SRC is shut). That sensed pressure is your signal to Scotty in the engine room of how hard you would like to brake. That's the end of your involvement; Scotty does the rest.

    Scotty handles the braking by looking at your pressure sensor signal, and linearly opening SLA to make pressure available to all four wheel pairs. SCC is wide open, so whatever pressure he arranges through SLA reaches all four pairs, and he can jigger the hold and release valve in each pair to take whatever fraction he thinks that wheel should take.
    When he opens any wheel Release valve, that fluid goes straight back to the reservoir. When he sees (by your pressure sensor signal) that you are easing off your braking, he can leave the Hold valves open and ease the total system pressure linearly through SLR, and that fluid also has an unobstructed path back to the reservoir (see page 43).

    It's only when Scotty gets a positive COVID test back and needs to go self-isolate that he throws the big red switch, and SSC and SCC slam shut, SMC and SRC pop open, and now you are personally in charge of the brakes. The front and rear brakes are now isolated from each other (SCC is shut), and none of the fluid you shove with your foot is going uselessly into a stroke simulator (SSC is shut). Instead, that fluid (from the forward master cylinder chamber) is braking the front wheels (SMC is open), and the fluid from the rear master cylinder chamber is braking the rear wheels (SRC is open).

    You can see that the only diagrams that ever show SCC and SSC closed, or SMC and SRC open, are the ones for fail-safe operation.

    Now, all of that still leaves a mystery as to why you may have seen what looked like blips of the switching solenoids in Techstream. I don't have an answer for that. But I'm pretty sure the above describes the operation they intended.

    I also notice that every diagram in that NCF excerpt is followed by a little table showing the condition of each valve, and a few of them (for VSC, TRAC, and hill-start) give the position of SMC as "open" in the leftmost column, breaking the pattern. Maybe it is possible they're doing something clever there with SMC in certain VSC, TRAC, or hill-start conditions. I can't rule that out. But there is no prose in any of those sections that says they are doing that, and it doesn't seem sensible on the diagram, and those probably weren't the kind of conditions present for your test drive, and my story is going to be that they made a typo for that one valve in that one column, and copied that table a couple of times.
     
  10. andreimontreal

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    I usually try my best. I do.

    Yes, I noticed that. I didn't analyze those diagrams too much but I read that too indeed. Overall, I took the general drawing for normal braking and imagined where the fluid could escape and why and if my readings could show any rear brakes blockage. And I'm glad there's none of that.

    I see what you're saying - I was in no special condition: flat ground in a residential neighborhood accelerating and braking as seen. I forgot about SLR for fluid relief (I made a mistake when I said that SMC/SLA are the only way for pressure to drop so cylinders could retract) - but I still think that it makes sense to open SMC/SLA to aid the brake cylinders retract as it decreases pressure/resistance 3x, vs 1x with only SLR open, and that would really make it easy for the cylinders to push back.

    Also, you say that SCC is wide open - but it only draws 0.6Amps most of the time. I've seen it at 1.1 Amps and the manual says that its max Amp draw is 3A - so it makes me think it's only partially open most of the time. Which would become a bit of a bottle neck for the front brakes as the cylinders are pushed back - so again opening at least SMC makes sense.

    In my head when they say "during normal braking" - I'd start thinking that if you're not braking then you're not under normal braking anymore so SMC/SRC can do whatever. So that was all in my head - trying to excuse SMC/SRC for the way they behave :D.


    Either way, whatever the reasons, it seems that the car's electronics are not at fault for that dragging.
     
  11. ChapmanF

    ChapmanF Senior Member

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    That would make sense if you were talking about a linear solenoid, the kind that has a range of opening, in some relationship to the drive current. But there are only two of those, SLA and SLR. (The ECU even has a little learning routine you can trigger in Techstream where it runs those at different drive currents and learns what different pressures it can make. Sometimes you can get a code saying it needs to do that again.)

    But drawing any conclusions from the drive current to a switching solenoid would seem a more dicey affair; those aren't supposed to have intermediate positions. The physics of why the current might be different from one reading to another could have multiple pieces; I would assume at least temperature coefficient is one of them, and maybe also the commonplace that it can take more work to make something move than to hold it moved.
     
  12. andreimontreal

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    You're right! You had to say it 2-3 times to fully register with me. 100% agreed.

    And what you say about needing more amps for varying conditions for opening that valve that is true and it explains it perfectly.
     
  13. andreimontreal

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    Update - this brake wants my life and nothing less :mad:: I got OEM Toyota bushings on RL thinking it will stop overheating like RR did but RL still gets hot. (Reminder: bot RR and RL brakes got new Raybestos Element 3 calipers this winter AND right after I got the booster replaced under the extended warranty).

    Here's the question now: IF I get an oem Tokico caliper in there and it still overheats - then - what else could be the problem? o_Oo_Oo_O . As seen above the actuators/booster seem to be working well. What else can I check

    At this point I'm thinking:
    1: There's something wrong in the RL caliper's piston.
    2. Could there be a problem something in between the caliper and the actuators?

    Idk idk idk :confused:
     
  14. ChapmanF

    ChapmanF Senior Member

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    I have never seen this myself, but I have read in more than one place about rubber brake hoses starting to delaminate, forming a flap inside that acts sort of like a one-way valve.

    You'd think you could notice if the fluid was staying pressurized, if you cracked open the bleeder and it came out more eagerly than usual.

    Have you ever just measured the return of the piston, with a dial indicator? I posted some on that way back when. I might have mentioned it before. Your saga has been dragging on for a while now.

    :)
     
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  15. andreimontreal

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    I did that a while back. There was no pressure without somebody pressing on the pedal.

    No - I even forgot about this and I'll see if I can figure a way to do that. The cylinder was on my mind strongly but I had no idea about that. My dad hoarded one of those machining measuring tools - let's see if I have everything to make it work. But after reading from your link, I'm thinking (1 where was my head when y'all warned me about buying oem) and 2 maybe it's best to get some Tokicos ... at the same time, if that fails, and it's "something else" again, I'd be really pissed.

    I still could get replacements under warranty from RockAuto ... just don't want to waste money on shipping when that could be invested in the Tokicos.
     
    #95 andreimontreal, Aug 19, 2020
    Last edited: Aug 19, 2020
  16. ASRDogman

    ASRDogman Senior Member

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    I have not read the WHOLE thread.... Have you replaced the rubber hoses for the calipers?
    If they have swollen inside, the rubber will expand under pressure and continue to apply pressure
    after the brake pedal is released, thus applying pressure to the pads....
     
  17. andreimontreal

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    No - because: I opened the bleeder valve and there was no pressure, no fluid coming out, so I assumed there is no liquid pushing back ASR so the lines would have to be good - I'm thinking. Right? or not?
     
  18. 2012 Prius v wagon 3

    2012 Prius v wagon 3 Active Member

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    For non-Prius cars (as I am familar with), you are exactly right. I assume same for Prius.

    If you have done everything you can with the brakes, and your symptoms are heat and drag, have you considered a wheel bearing problem? Heat will conduct back there, so anything that gets hot will make everything hot.
     
  19. andreimontreal

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    I still have to check what Chapman said - the piston's function. And by now I'm heavily convinced it's there. On RR when I checked the pins a few days ago it seemed I had more space to install the caliper back vs RL which is always tight and hard to put back. So I think it's not retracting properly. I'm just about fed up with this Chinese crap, looking to see what's the cheapest source for Tokicos - gonna make this car run for another 15 years dammit.
     
  20. andreimontreal

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