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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. ChapmanF

    ChapmanF Senior Member

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    I just read this over again from the top, and saw that introductory sentence saying this is a 2004 with 45k. Are those miles or km? Either way, that's remarkably low usage for a 13-year-old car, and maybe lends even more support to the NHTSA idea that significant periods of disuse (much like the RV use pattern) are what allow the phenolics to soak up water and swell.

    Has there been a change in circumstances so it will be more consistently driven in the expected future—or, once the brakes work, I mean? If so, I imagine it will be just fine with new OEM-spec phenolics, just let Toyota sell you a couple of those and another rubber kit to replace the seal that got pinched, reassemble and expect years of trouble-free use.

    Even if you find a supplier of metal replacement pistons that fit, I think the engineering choices at work are surprisingly subtle: in my own experience with the third-party rebuild that arrived with zero piston return, I suspected part of the problem might have been their use of a different metal piston—the OEM piston for Gen 1 was metal, but with a more coarse/dull surface finish, where the rebuilders used one that was downright shiny, and I wouldn't be shocked if the friction coefficient between piston and seal were one of the parameters affecting the return behavior.

    So, again, if the circumstances are changed so the car can expect a more consistently-driven future life, I think the Toyota original pistons are most likely to function well all around, and will probably last and last.

    -Chap
     
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  2. harryarcos

    harryarcos Junior Member

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    The UK is still using miles, although the metric system was generally adopted in the early 1970s. The car has been in constant use albeit for short journeys, but it is not that rare in the UK to find vehicles with average annual mileages of between 4 - 5,000. - Insurance policies even cater for those with low annual mileage, offering discounts.

    Regarding the pistons soaking up water, this could only happen if the material is hydroscopic. Most of the piston is inside the caliper housing or covered by the rubber boot, which should be protected by brake grease (red) and there was no sign of corrosion in or around the caliper. Having tried the steel alternative, I might be forced to now buy the phenolic ones, but apparently these are not stocked in the UK and have to be imported at a cost of about $25 each. Nobody at the Toyota dealership appeared to recognize the swelling of pistons as a problem, but no surprise there!

    If I knew at the beginning of the month, what I now know, then I would just have replaced the whole caliper with something like the 'Brembo' alternative, rather than Toyota rebuilds as Mendel suggested. However, at the risk of 'throwing good money after bad' I would like to find out whether new phenolic pistons solve the problem. I will let you know in due course.
     
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  3. Mendel Leisk

    Mendel Leisk Senior Member

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    Insurance cost reduction for low use would be good for us, but I've never heard of it here. Interesting. Good for the environment too: encourage conservation.
     
  4. ChapmanF

    ChapmanF Senior Member

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    It's hard to wave away those box plots from the NHTSA testing, showing exactly that....

    I seem to recall in Boston (at one time, anyway), car insurance could be discounted if you could show you'd purchased a yearly public transit pass.

    -Chap
     
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  5. harryarcos

    harryarcos Junior Member

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    I would not wish to mislead anyone, but I am clearly way out on any difference between the diameter of the bore and piston. I am unable to find anything on the web, so experimented with a plastic tub and sellotape to discover that 0.2mm is more than enough for the piston to drop easily into the bore. Engineered using precision equipment, it could be as little as 0.05mm so if anyone knows for sure, please share the info.
     
  6. harryarcos

    harryarcos Junior Member

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    A result at last! After the supplier of the new pistons assured me that they were the correct part, I stripped the O/S caliper and the new piston fitted perfectly. On closer inspection of the N/S caliper bore, I could detect a very slight ridge just below the grove for the gasket, extending for about a third of the circumference. A little work with abrasive paper and the piston went in. The ridge must have been there since it left the factory and explains why the pads on that side had worn to 2mm in 45K while there was still about 8mm on the other side. It also perhaps, explains why there were only 2 shims on the N/S. My guess is that the slight binding or pad wear on that side was picked up during a service and they simply removed a couple of shims. Great job Toyota.

    If anyone is interested in my previous post regarding piston/bore clearances, I did eventually find this from an aviation forum:

    Brake piston to bore clearance - VAF Forums
     
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  7. Travis Sanders

    Travis Sanders Junior Member

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    I've been a mechanic for 25 years. These plastic Pistons get stuck often especially after getting too hot. The metal Pistons get stuck mainly if they get rusty. I like the metal Pistons if you grease them well. use Dot 4 instead of Dot 3 so the fluid can handle higher temperatures. The grease will keep the rust away. I've got three Toyota Priuses. One is a 2004 & the others are 2005. The plastic Pistons all got stuck. I ordered brake calipers from RockAuto that claimed to have metal Pistons. The one with the bracket came with a metal piston. The one without the bracket came with plastic piston. I'm so tired of plastic Pistons swelling up. That's why I ordered these metal ones, now I'm all frustrated because one showed up with plastic.

    One of the Priuses has to drop 3000 feet in elevation in only 5 miles and then back up the hill several times a day. That's a 20% grade that takes a long time with a speed limit of 25. At times the B mode is not enough to keep it under 50 miles an hour. This poses a large problem for a Prius. I find if I go extra slow when possible and go way too fast whenever possible I can get to the bottom without smoking the brakes. The regenerative braking does no good because the Hybrid battery is full after only 1/4 Mile and doesn't provide any further help slowing down the Prius. Turning on the rear defrost air conditioning and everything electrical I can think of helps a little bit. B mode is frustrating because it combines engine braking and high regeneration. I'd like to save the regen ability for times in which I needed it the most. It's not exactly a steady grade. Maybe I could drag a refrigerator or a used sofa or something down the hill that'll keep me slowed down.
     
  8. ChapmanF

    ChapmanF Senior Member

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    Will you use metal or plastic feet on the legs of the sofa?
     
  9. dolj

    dolj Senior Member

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    Not true, it combines higher engine braking with lower regeneration so that the HV battery takes longer to fill up. Unfortunately, in your case, you would have to apply some additional light to medium braking which will increase the regen into the battery until the HV battery is full. But there is still good news, in that once the HV battery is completely full (i. e. 8 Bars on the Energy screen or 80%) it will switch off regen and replace that with even more engine braking. Done right you should not be using any significant hydraulic braking, so you never should have "smoking (or even heated) brake pads or rotors.

    If your car is not behaving this way, it may pay to investigate why.

    And, FWIW, your scenario will be very hard on the HV battery, so maybe getting to the point where it is just plain worn out.
     
  10. Mendel Leisk

    Mendel Leisk Senior Member

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    ICBC (crown corporation, the main auto insurer in British Columbia) now offers 10% insurance reduction if you drive under 5000 kms (~3000 miles) per year. I gather you need the insurance agent to check the odo, then recheck the next year.

    We're borderline, previous years around 7~8K kms, but I'm kinda kicking myself for not trying for it: with COVID I think we would have been eligible this time around. Oh well, next year.



    Statement from ICBC president and CEO on the BCUC’s decision


    The above is a little presumptive, saying you need to provide (dated) photo of the odo within 7 days, kinda presumes owner has a smart phone capable of such (metadata tagged) photo. I'm sure in a pinch the agent could just walk out to the car, take the pics. More secure that way too, less fraud.



    Sorry I'm off-topic btw.
     
    #50 Mendel Leisk, Jun 13, 2020
    Last edited: Jun 13, 2020
  11. Douglas cadete

    Douglas cadete New Member

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    On generation 2 the minute you open the bleeding screw and pressure is depleted you will definitely get a code. And it can only reset with scanner that read Toyota abs codes. Standard obd2 machines won’t be good enough to clear this code. Valves inside the brake/abs module will be stuck in wrong position until it is reset. Brake pedal will seat in very high and hard.
     
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