Remove brake fluid contamination by diffusion?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by pasadena_commut, Jun 14, 2024.

  1. pasadena_commut

    pasadena_commut Senior Member

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    Flushing the Gen 2's brake fluid successfully is quite difficult. Toyota's suggested method is to use Techstream, but it may or may not work with a given cable. There is another method

    Replacing brake fluid and bleeding brakes on a GEN II Prius without Techstream | PriusChat

    that doesn't need Techsteam, but it is fairly involved too. So I wonder how beneficial it would be to just change most of the fluid in the reservoir periodically and wait for all of the fluid in the system to come to equilibrium.

    The diffusion rate of all the molecules in DOT 3 may be very slow, but if the system was well modeled as a reservoir connected to four very long tubes, then it would eventually come to equilibrium, even if it takes a month or three to get there. Do this 5 minute fluid swap at 6 month or 12 month intervals and eventually it would be equivalent to a traditional flush (except it would not remove any sediment in the lines.)

    The thing is, I suspect that simple model is not a very good one for this car. The ABS unit has some complex logic in it, and some of the fluid locations within it are not going to be in contact with the rest of the fluid unless the ABS is active. I'm not even sure that the fluid in the reservoir is always in contact with that in the master cylinder, as there may be a valve or two in the way. If the connection from the reservoir to the master cylinder was only open intermittently, then the time to come to equilibrium could be years and then this simple method just wouldn't be practical.

    Thoughts?
     
    #1 pasadena_commut, Jun 14, 2024
  2. Tombukt2

    Tombukt2 Senior Member

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    Vacuum at each wheel . I guess what won't pull through I can undo the lines at the actuator and pull on those from the other way eventually I should get most of it out reasonably quickly and then just fill it w dot 4 . I'm going to try purple silicone in one when I get around to it just to see what happened It's been in my Corolla AE11 for about oh my goodness 15 years I had to do some work the other day on the front brakes and let a little bit out it's still nice and purple and the brakes have been spot on on this car for this whole time the reservoir fluid is still purple when you shine a light through it the reservoir is starting to turn white but it's worked very well everybody said it wouldn't and there would be problems and so on and so on and there have been none and believe me we have taxed the brakes on that AE11
     
    #2 Tombukt2, Jun 14, 2024
  3. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    My understanding matches yours, and based on that I'd say doing a flush without techstream (or other tool capable of exercising the valves) would just be a waste of time and good brake fluid.

    You'd be leaving water (or other contaminants) in the single most expensive part of the system, while flushing it out of the cheapest parts.
     
    #3 Leadfoot J. McCoalroller, Jun 14, 2024
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