Brake fluid gone in 3 months after brake booster & master cylinder replacement

Discussion in 'Prius v Care, Maintenance and Troubleshooting' started by mkomko, Sep 8, 2025 at 12:34 AM.

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  1. mkomko

    mkomko New Member

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    We have a 2014 Prius V with 95k miles that needed the master cylinder and the brake booster replaced in June. It was costly but we did it. After 3 months of driving, the brake light came on and off a few times as I was driving this morning. I didn't notice anything strange or unusual when braking. I opened the hood and realized that the brake fluid wasn't really there. It was Sunday so hybrid specialized mechanics weren't available, so I took it to Pep Boys and had the brake looked at. The mechanic said the pads and the brake drums are fine, but the fluid is very low. Googling around I couldn't figure out if it was okay to add some fluid without draining it so I drove it home. The brake light did not come back on during this10 mile trip. I couldn't tell exactly how low the fluid was. If it is the yellowish stuff, it was below the minimum line. I ended up getting some fluid and added to it. I paid attention to the line but I only saw the line move above the minimum line (also the reservoir's parting line). It was hard to tell. I tried to look for a sign of leak but it's hard to tell for me without removing the reservoir etc, but maybe two black tubes behind the reservoir are looking a little greasy.

    We had the brake booster and master cylinder job done at a mechanic that quoted the cheapest and located the closest, not at our usual Prius mechanic who we trust. We didn't go with them due to costs and timing issues. The new guy has decent reviews online. We regret it big time but it's been done. We do worry that the new booster/cylinder parts are compromised due to internal leak. Is such a thing possible due to a bad assembly job? We will try and talk to them both and see what could be done, but if there's anything we should consider, I'd like to hear! We don't really want to work with the same guy. We are also not sure if it's okay to drive 20 miles to our usual mechanic.
     

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    #1 mkomko, Sep 8, 2025 at 12:34 AM
    Last edited: Sep 8, 2025 at 12:48 AM
  2. ChapmanF

    ChapmanF Senior Member

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    That fluid is definitely way too low. Fluid doesn't go away like that unless there's an external leak (fluid actually leaving the system). There will be a gooey spot somewhere, near a brake line or connection. Given the recent replacement of the actuator, I'd guess the gooey spot is probably near where those connections are made. Unless there is a simple coincidence, and those do happen.

    Some leaks can be hard to find. I had a rusty brake line once in another vehicle that had cracked, but the crack would only spread open and leak fluid when the pedal was stomped really hard. Then it would shoot a jet of high-pressure brake fluid and the only gooey spot was where that hit the rocker panel clear across on the other side of the car.

    Be careful, by the way, when searching for that kind of leak. A high-pressure fluid jet like that can go into skin and do what seems only minor injury at first but becomes grievous without immediate medical attention.

    I found that one by draping shop towels over the brake lines and then going safely up front to stomp on the brake pedal, and then looking for the shop towel with the wet spot.
     
    #2 ChapmanF, Sep 8, 2025 at 10:31 AM
  3. Georgina Rudkus

    Georgina Rudkus Senior Member

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    It might not be a leak, but an improperly bled system after installation.

    The Prius braking system requires a special procedure for bleeding the brakes best done with Techstream.

    This is one time I'd have it done by a Toyota dealer.
     
    #3 Georgina Rudkus, Sep 8, 2025 at 11:08 AM
  4. ChapmanF

    ChapmanF Senior Member

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    The reservoir is wide and holds quite a lot of fluid. Even the amount the level drops when pumping into the accumulator from zeroed-down condition is only several mm. The next biggest volume to fill would be, I think, the stroke simulator. It's hard for me to picture the reservoir this low from "an improperly bled system after installation" even if that meant installed empty with no attempt to bleed it at all.

    OP. do you remember what the fluid level in the reservoir looked like right after the assembly was replaced?
     
    #4 ChapmanF, Sep 8, 2025 at 11:49 AM
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