Observations, and a Question re: Front Brake Pad Replacement

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Patrick Wong, Jul 12, 2020.

  1. Patrick Wong

    Patrick Wong DIY Enthusiast

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    My daughter's 2007 has logged 144K miles. She is able to "work from home" so she has been visiting with my wife and me over the past three weeks.

    I replaced the engine oil/filter and the rear hatch wiper rubber. Yesterday I replaced the front brake pads which were down to 3 mm thickness, and also replaced the 12V battery (six years old) as a preventive measure, trying to bring the car back up to a high standard before she departs next week.

    This is the first time that I have done Prius brake work despite owning four Prius:

    I sold the 2001 before it needed brake work
    The 2004 had front brake pads installed by a Toyota dealer as my daughter had the car in southern CA at the time
    The 2015 currently has 34K miles.

    I noticed other threads about the use of the Toyota pink lithium soap base glycol grease to lubricate the slide pins, and bought that grease from a dealer via eBay. The slide pin rubber dust boots were in good condition so I did not replace them. (I would not use an alternative to the lithium soap base glycol grease; such as silicone grease.)

    The slide pins were in good condition. When I pulled them out, the residual grease looked OK. So I wiped off the pins, put more grease on, and reinserted them. They moved freely, no problem.

    To lubricate the brake pad anti-squeal shims, I used black CRC brake caliper grease which came in a bottle with a brush attached to the lid.

    Prior to starting the brake job, I disconnected the 12V battery and removed it. Noticing that the battery was six years old I decided to replace it as a preventive measure, and bought a GS Yuasa battery from a local Toyota dealer. The battery had the GS Yuasa labels and also the TrueStart label, 24 month 100% warranty, and 84 month prorated warranty.

    The front discs measured 0.82" in thickness which was halfway in the spec which ranges from 0.787" to 0.866". So I left the original discs in, although I had bought new discs.

    After completing the job, I depressed the brake pedal several times to take up the slack between the caliper pistons and the new brake pads. Then I installed the new 12V battery and took the car for a test drive. Happily, no warning lights appeared.

    I got the car up to 40 mph, shifted to N, and braked the car a few times to make sure the friction braking was working fine. It was, the car stopped in a straight line without me holding the steering wheel, so both sides exerted similar braking force.

    My question:
    I was expecting the brake fluid level in the reservoir would rise as I used a C-clamp to push the caliper piston back into the housing. However the level did not change at all, which really surprised me. Has anyone else noticed this?
     
  2. MickyMatter

    MickyMatter Active Member

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    I replaced the rear pads (In Europe there are disks in the rear, too) last December.
    I've made the same experience: While doing the job, I've forgot to check the fluid level and remembered only, after I'd pushed the brake piston much further back into its cylinder with a F-clamp. Worried about making a mess with this aggressive and paint removing brake fluid, I've checked immediately the reservoir. But there wasn't any change.
    After finishing the job and with much thicker pads than the old worn ones, there wasn't any change, too.
    I mean, it's much better, than making a mess! But I wonder, why, too.

    [​IMG] [​IMG] [​IMG]
     
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  3. Mendel Leisk

    Mendel Leisk Sand Pounder

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    With 3rd gen at least, there's a phenomena: if the car sits at least day, and you go in through the front passenger side, pop the hood and check brake fluid level, it'll be quite high. Then go around and open driver's side door, a pump will start up, and fluid level will drop maybe 3/4" inch. If you're quick you can see it dropping as the pump whirs.

    Maybe something like that's a factor in your before/after fluid level check??
     
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  4. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Yes, I noticed that with my 2015. The Classic and 2G Prius show different behavior, in that the brake fluid reservoir fluid level will remain constant, unlike the 3G activity you described.
     
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  5. ChapmanF

    ChapmanF Senior Member

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    That has to be an artifact of when you looked. Even Classic and 2G have accumulator chambers, and when they pump the fluid into them, the reservoir level is going to go down. There reeally isn't any other choice.

    How slowly the reservoir level rises again while the car is off is a measure of how well the valves in the system hold pressure.

    Of course, Classic would not start the pump until you turned the key. Later ones try to get a jump on things by starting the pump as soon as you open the door.
     
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  6. Patrick Wong

    Patrick Wong DIY Enthusiast

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    You may be right. I have the Prius hood open for extended periods frequently, charging the 12V battery via the jumpstart terminal in the main relay/fuse box. This allows me to observe the fluid level in the brake fluid reservoir over time, among other things, and I could see that the 2015's fluid level moves between the MAX line and the unlabeled line below MAX, depending upon whether the system is pressurized.

    However, I am comfortable with my observation that the brake fluid level in the 2007's reservoir was at MAX before I started working on the brakes, and remained at MAX after pushing in the brake caliper pistons on both front brake calipers. Even after restoring 12V power and driving the car around, the fluid level remained constant.

    It seems to me that the pressure accumulator might have its own little reservoir, or at least the ability to absorb the additional amount of fluid that I pushed back up via the front brake lines, since the additional fluid did not end up in the fluid reservoir.
     
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