Brakes + Brake Fluid Question

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by darkgiant, Oct 8, 2018.

  1. ChapmanF

    ChapmanF Senior Member

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    Or zip the file and upload that (.zip is an allowed extension).

    YouTube is easy, but it's also silent for me at the moment, so I wouldn't be of much help. :)
     
  2. ChapmanF

    ChapmanF Senior Member

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    I just took advantage of nice weather this afternoon to do a partial fluid change ... that is, to go through the bleed procedure, and use new fluid to make up for what was bled out.

    I had been noticing some extra squirty noises when braking, and I had my theory that nitrogen escaping from the accumulator into the plumbing might account for that, so I wanted to try the bleed procedure and see if any significant bubbles came out. I used the longer bleed procedure for "ABS actuator has been replaced" even though it hadn't been, just in case there was any gas trapped up there. The longer procedure includes removing the windshield wipers and cowl for access to the bleed screw on the stroke simulator.

    The long bleed procedure steps you through the following:

    • Bleed the rears, first right (longest distance), then left. For these you can just wedge the pedal down, go around back and open the bleeder; the pump will run to keep sending you fluid as long as you need it (don't run the reservoir dry!).
    • Bleed the fronts, first left, then right. This requires pumping the pedal, because you're bleeding the fail-safe part of the plumbing that will work if the electronic controls fail.
    • Bleed the stroke simulator. This also involves pedal-pumping.
    • Bleed the fronts again. This time it works like the rears, it's bleeding the electronically controlled parts, so just open the bleeder and it pumps fluid at you.
    • Then it completely zeros-down and refills the accumulator, six times, presumably to let any bubbles in that area find their way back to the reservoir.
    • Then it tells you to power the car down, reconnect the reservoir level sensor, and power on with the parking brake off, and it "learns" the linear solenoid offset. The learning took no time today, presumably because it had already been learned and it would really have gone through that if the actuator had really been replaced.

    I think I noticed some small bubbles but nothing really attention-grabbing. I've made one short trip since, not really enough to decide if the squirty noises I was hearing are improved.

    I used the Tactrix dongle this time instead of the Mini VCI that I used the last time I ran a bleed procedure, and I'm happy to report there were no "communication lost with vehicle" flake-outs during the procedure, as I had had with the Mini VCI. The MVCI had kept flaking out on like the fifth or sixth zero-down-and-refill at the end of the process and having to start over from the top; my accumulator must have had maybe thirty full cycles put on it by the time that nightmare was over. Today the Tactrix just marched through the six repetitions with no issues, and was done.

    I actually did get one "communication lost" error. The procedure took long enough that (even though I had a second 12 V battery paralleled in back), the car turned itself off at one point. I saw the "lost communication" alert box and thought "oh no, not this dongle too!", especially as I told it to retry and it was totally unable to reconnect. Then I noticed the car was off. :) Turned it back on and restarted the procedure from the top, just skipping the steps already done, and finished without any other issue.

    I took the opportunity to save some of what came out the RR (farthest off dead end fluid trap) and dunk a brake fluid test strip in it (145,xxx miles, unless the previous owner did a fluid change I don't know about) and it looked very good:

    brake.jpg

    I'm reading that as somewhere between 10 and 30 ppm. This is in line with hobbit's result at the end of his 100k maintenance page. Being in a Prius seems like a very easy life if you are brake fluid.

    The other end of the strip has test swatches for coolant. It's been about three years since I changed that, so may as well dunk:

    cool.jpg

    The concentration color doesn't seem to have photographed well, but to my eye it looked a little more like 60% than 50%. Which is weird, because SLLC is pre-mixed. The pH swatch seems to match a nice neutral 7.

    At the left of the photo you barely see the strip of Scotch tape, a few inches long, I had to wrap over the "brake" end of the test strip to be able to dunk it deep enough in the coolant reservoir to hit both swatches (and pull it out again). Maybe the concentration swatch came out extra dark because it got double-dunked (once before I thought of the tape).

    The coolant reservoir in a Gen 3 is the newer "degas bottle" style that is part of the circulating fluid, so it's a reasonable place to use a test strip. In a Gen 1 or Gen 2, it would probably be better to use the radiator filler neck, because in those generations the plastic bottle was just the old-fashioned overflow bottle, and the coolant in it might not represent what's in the engine.
     
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  3. ChapmanF

    ChapmanF Senior Member

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    I should add: all of the bleeders were easy-as-pie to open, like the day it rolled off the lot.

    I credit the rubber caps Toyota puts on all the bleed screws.

    I grew up around cars without those rubber caps, where the salt water would run in through the passage and rust the threads from the inside, and every brake job was a little adventure: will I ever get the bleeder open? will it break off? should I buy another caliper in advance in case I need it?

    Bleeders that just open right up with a touch of the wrench are heavenly.

    Moral: don't lose the rubber caps off your bleed screws, and put them back when you're done. They're not just decorative. (If you find one that is cracked or deteriorated, there are new ones included in the caliper rubber kit; they can also be bought a la carte).
     
  4. Mendel Leisk

    Mendel Leisk Obtuse Angler

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    Maybe give those caps a twist whenever you're doing the brakes, and apply just a thin wipe of silicon around the outside.
     
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