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Front brakes stuck after fitting new pads

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by harryarcos, Feb 18, 2017.

  1. harryarcos

    harryarcos Junior Member

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    Hoping you guys might be able to help me move this 2004 Prius with 45k on the clock. Nearside (Offside on your side of the pond) front pads had worn to about 3mm against 8mm on the opposite side, so thought it a simple enough job to renew both sides by pushing the pistons back into the calipers (Advic) and installing new pads. The pistons moved freely enough and the caliper pins were well lubricated.On road test, only moved a few yards and could feel that the brakes were binding. After less than a mile the discs (rotors) had reached about 180℃.

    I reinstalled the old pads, thinking that perhaps the new ones were too thick, but the same thing happened and the 3 yellow lights came on. A friend cleared the lights, but could not find any fault codes. Relays and fuses all OK. Another road test and no difference.

    It feels like the fluid is not returning to the reservoir and there are one-way valves operating along the lines. I am hoping that it is not the ABS/Pump (which appears to be one of the most expensive) but the only other culprits I am able to think of are the brake hoses.

    Having searched the Forums, I found ABS/Pump failures where there was insufficient pressure, but none where there was too much. Wondering if anyone else has had similar problems? Any help would be much appreciated.
     
  2. jzchen

    jzchen Newbie!

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    Try renewing, is that the correct term for you, the brake fluid first.
     
  3. Mendel Leisk

    Mendel Leisk Senior Member

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    Have a dealership flush the brake lines, and alert them to your issue?

    I appreciate it (brake fluid change) can be a DIY, but at this juncture it might be better to get them on it, and troubleshooting. I know on third gen you need to put the car in special mode while bleeding, if you don't have Techstream.

    Has the brake fluid ever been changed? Tri-yearly is a good rule of thumb.
     
    #3 Mendel Leisk, Feb 18, 2017
    Last edited: Feb 18, 2017
  4. jzchen

    jzchen Newbie!

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    Could be a failure in the sensor for the brake pedal. Only the front?

    Tires all the same size, about the same wear/tread depth?
     
  5. jdcollins5

    jdcollins5 Senior Member

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    Mendel,

    Don't the caliper rotors have to be turned to a particular position to align with the back of the brake pads?

    Could this be part of his problem?
     
  6. Mendel Leisk

    Mendel Leisk Senior Member

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    2nd gen rears in Britain are disc not drum? But still, OP's saying it's front brakes he's done.
     
  7. ChapmanF

    ChapmanF Senior Member

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    There's a recommendation I've frequently seen online, for any car that has elaborate ABS valving upstream, to never replace pads by forcing fluid from the caliper back up into the valving. The recommendation instead is to open the bleeder at the caliper before pushing back the piston, so any gunky fluid from the caliper simply leaves the system, then button it all back up and make up the reservoir level with fresh new fluid.

    The concern is to avoid pushing any gunk back up into the delicate ABS valves that might stop one of them from completely re-seating. If one can't completely close, it could be allowing some amount of pressurized fluid to the caliper even when you're not trying to brake. This is the sort of rare thing you could do 99 brake jobs and get away with, but run into as an expensive headache one time in a hundred (which is always most annoying if that one time happens to be the first one you do!).

    If that might have happened, then it's also possible a good fluid flush, exercising all the ABS valves, might help, before making any harder decisions.

    For what it's worth, I was once in what I thought might be that situation, and it turned out I just had a caliper with inadequate return, which is pretty easy to measure and easy to fix, so that's worth checking. It's especially worth checking since you report the pads so much more worn on that side than the other side to begin with.

    -Chap
     
  8. Mendel Leisk

    Mendel Leisk Senior Member

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    Yeah missed that.
     
  9. harryarcos

    harryarcos Junior Member

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    Thanks for all your quick input. I doubt that it is a problem with the fluid, as it was changed by a Toyota dealer about 2 years ago. Nonetheless, how I wish that I had clamped the hoses and cracked the bleed nipples when I forced the pistons back into the calipers. I did do it that way after putting the old pads back and then returning the new ones, but the fluid was very clean.

    As you all know, you do need one of those hand-held testers to bleed the brakes properly and mine is somewhere between the UK and China! When it arrives, I might as well bleed the brakes and keep my fingers crossed. Still wondering about the hoses, as I hear that it is becoming more of a problem - insides breaking down and preventing fluid returning, but does anybody know whether a fault such as the valve sticking in the ABS/Pump would throw a fault code?

    In 40 years Saab ownership, I only needed the dealer on a couple of occasions and one of those was to programme a new key on the Tech 2 equipment, so I will keep at it for a while. If it turns out to be the ABS/Pump then all the money and more that I have saved on fuel is going to buy a new part. Still much less stressful siting in traffic in a Prius than a V6 Saab!
     
    Mendel Leisk likes this.
  10. harryarcos

    harryarcos Junior Member

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    By the way, thanks ChapmanF for the link regarding piston return. Never heard of it before and very interesting. Could well be the reason for differential pad wear, but there is no 'give' at all in the present situation.
     
  11. andrewclaus

    andrewclaus Active Member

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    I would rebuild/re-hone, or replace calipers first.
     
  12. valde3

    valde3 Senior Member

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    Would be better to find out where the problem is before just changing parts.

    First maybe you should make sure that pads can move freely in their shims.

    If that’s not the problem:
    Put the brakes to manual mode (only front brakes with no ABS or power assist) by pulling the two relays and using all the pressure: Brake service
    If you can then get it to bind (you need to use lot more force) then it really can’t be the brake actuator. Then once it’s still binging (in manual brake mode) you can loosen the brake bleeder. If it then loosens immediately you know it’s not the problem with brake caliber. That pretty much just leaves the brake hose.
     
  13. harryarcos

    harryarcos Junior Member

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    Thanks for the link and suggestion. I will give it a go. Very easy to spend a lot of money just replacing parts in the hope that it fixes the problem. Have read on here that Toyota have had a lot of problems with these ABS/Pumps (or Actuators) on Prius models and have extended the warranty to December 2017. No idea whether or not it applies to the UK, but I will look into it!
     
  14. jdcollins5

    jdcollins5 Senior Member

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    Toyota US replaced the Gen 3 Brake Booster Pump under warranty and supposedly tested the rest of the braking system.
     
  15. harryarcos

    harryarcos Junior Member

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    I believe mine is Gen 2 (Dec 2004). I have tried removing the 2 blue relays and applying the brake 30 odd times, but the brakes are still firmly stuck on. After taking it a few hundred yards down the road and back, the discs reached a temperature of 90ºC. I do not how the internal valves etc. work in the ABS/ Pump (Actuator) but would the general opinion be that the unit is OK and that the fault lies within the calipers and or hoses?
     
  16. 05PreeUs

    05PreeUs Senior Member

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    No, utter hogwash perpetrated by those wanting to upsell services or parts.
     
  17. 05PreeUs

    05PreeUs Senior Member

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    There are THREE possibilities:
    1) Binding caliper slides - if you take the pads OUT and refit the calipers, the caliper(s) should move FREELY in-out on the pins
    2) Hydraulic issues - if you open the bleeder screw(s) *slightly* and pressurized fluid escapes, it's the HCU
    3) Sticking caliper piston - this is the most difficult to dis/prove, but if other causes are ruled out, a reasonable conclusion

    While service manuals commonly list a damaged hose as a possible cause, in 40 years of doing brake work, I have never once seen it.
     
  18. harryarcos

    harryarcos Junior Member

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    No problem with the caliper pins/slides - very easy to push in and out. Pistons also seem to be moving as well as any other piston which I have had to move back on other vehicles using a 'C' clamp. As for the fluid, it does not seem to be under great pressure when the ignition is off, as it is fairly easy to remove the calipers from the pads and I would have thought that the piston would shoot out, if under high pressure.

    You have given me an idea, which is to open the bleed screw slightly while the car is in 'P' with the ignition on and then see whether the fluid comes out under high pressure - I normally fill a clear plastic tube with a small amount of brake fluid before pressing it onto the bleed nipple to prevent air entering the system. I am guessing that if fluid does come out under pressure, then it would definitely point to the control unit for the ABS/Pump. Do you know if this is managed by the ECU or all within the unit? I guess a clue would be to look at where the info.from the stroke sensor goes?

    Thanks for your input.
     
  19. Mendel Leisk

    Mendel Leisk Senior Member

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    Would opening bleed valve cause the car to throw a code? On third gen there is "invalid mode" to circumvent this, if you don't have techstream.
     
  20. ChapmanF

    ChapmanF Senior Member

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    If it were me I think I'd definitely check the calipers for return—if only because it's not too hard to check, and it did turn out to be the problem the last time I was having hot-rotor-after-driving issues, and there's a bit of cargo-cultist in us all.

    I was testing with the caliper off the car, just using puffs of compressed air. I think it wouldn't be very hard to adapt that to an on-car test, if you had a longish hose to fit over the bleed screw and route upward. If you let some fluid bleed out, part way up the hose, it should then be possible to puff air in at the hose end just enough to nudge the piston outward and measure its return, without getting any air in the caliper. (The rest of the setup would be as I described in the earlier post, just blocks of some hard material about the same thickness as rotor+pads, and a dial indicator.)

    The key is using only a puff, enough to lightly bonk the piston out against the block, then measure the return. It might be tempting to try to do the same test using only the brake pedal, but the hydraulic system is so powerful you end up measuring the elasticity of aluminum and steel and not the piston-seal return if you do it that way.

    If the ECU sets codes while you're playing, just clear 'em later, no biggie. You could view them as reassurance that it's paying attention. :)

    But you probably want it in Invalid Mode (or the battery disconnected) while having the bleeders open, just so it doesn't happen to schedule one of its occasional self-tests, and squirt you.

    -Chap