Rear drum brake cylinder leak after push through

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Lento47, Aug 7, 2026 at 6:18 PM.

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  1. Lento47

    Lento47 New Member

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    Finished doing a front brake job (pads and rotors) on my 2009 Prius, then noticed the backs were a little squeaky, so pulled the drums off and did a thorough cleaning (they were very dusty). I also pulled the components (brake pad brackets, star adjuster), particularly to clean the star adjusters. When reassembling the Drivers Rear drum, after finally getting the main spring (around the star adjuster) back on, I saw that I had inadvertently pushed the cylinder/piston all the way forward (though not enough for the end caps to come off). I re-centered the cylinder/piston and then pulled back the cylinder end covers to inspect and found fluid in the rear one. It dripped a tiny bit and I quickly put the end cap back on.
    Note, I pulled the battery (-) and also the relays for all this.

    Could I have permanently damaged the internal cylinder seals?
    I plan to remove the rear end cap again and sop up/ remove any fluid in the cap, dry off, then reinstall. Then reassemble/put the drum back on and try pumping the brakes, then reinspect for fluid leaking.

    I assume that if it leaks after testing, I need to replace the cylinder.
    But if it doesn't continue leaking, am I good to go?
    or perhaps do a bleed on that line to be sure no air got in?
    Or do I need to replace that cylinder now either way?

    It's a 2009, but only 85,000 miles, and as far as I know, these are the original rear drum brake cylinders.
    Any advice would be welcome!
    Thanks!
     
    #1 Lento47, Aug 7, 2026 at 6:18 PM
  2. PriusCamper

    PriusCamper Senior Member

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    Back in the 80's seemed like every old car had a problem like this... So much so that most mechanics wouldn't start working on brakes on an old car unless that part was nearby. But first time I've read about it in a Prius. Sounds like a minor leak was there but made worse when cleaning?
     
    #2 PriusCamper, Aug 8, 2026 at 3:58 PM
  3. Tombukt2

    Tombukt2 Senior Member

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    When you go to put the spring back on it's easy to make one side of the SHOe to cylinder assy. Can get missligned and this happens. You also have to adjust the rear shoes way out so that they're scraping the drum everything has to be correct or piston will. Pop out enuff to leak .
     
    #3 Tombukt2, Aug 8, 2026 at 4:02 PM
    BiomedO1 likes this.
  4. BiomedO1

    BiomedO1 Senior Member

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    I never do a tear-down cleaning of drum brakes; unless I'm replacing the shoes. It gets brake clean spray down and grease on the shoe to back-plate rub points. Drum gets put back on and star adjuster is cranked out until it scrapes the drum during rotation. That's usually all it needs. You'll find your manual parking brakes works much better after making that adjustment.
     
    #4 BiomedO1, Aug 8, 2026 at 4:16 PM
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