I improperly installed a master cylinder. This punctured a hole in the cylinder. I didn't realize this until I pumped a gallon of brake fluid into my booster. How do I get it out?

2014 jeep wrangler unlimited rubicon

  • Buy a new one. If you punctured the membrane then it won't work. And the chances of you correctly replacing the membrane... That is assuming you can get a new membrane.
    – Solar Mike
    Sep 3, 2019 at 4:29
  • I am getting a new master cylinder, but the brake booster still seems to function ok. It's just oozing with brake fluid.
    – Josh C.
    Sep 3, 2019 at 11:33
  • How did you test the booster to know it is functioning ok?
    – Solar Mike
    Sep 3, 2019 at 11:59
  • @SolarMike do you think I could have damaged it too? It was brand new. I'm not sure how to test it, but if I actuate the plunger the fluid seems to suck back and forth between the inner chamber.
    – Josh C.
    Sep 3, 2019 at 13:31
  • Brake boosters don’t move fluid, they work on air pressure difference...
    – Solar Mike
    Sep 3, 2019 at 13:33

1 Answer 1


You'll need to remove the booster from the fire wall of the vehicle, then drain it out, then use some acetone to clean it out. Let it dry, then re-install. If it continues to work correctly, you're in business. If not, you'll need to buy a new one or at the very least, one from a wrecking yard as a replacement. Unfortunately, you probably won't know if it's still going to work until you get it back installed. More than likely, there will be either two or four bolts on the fire wall. Could be inside the passenger cabin to get access or might be in the engine compartment. You'll also need to disconnect the booster from the brake pedal, but that's usually just a rod with a pin/clip arrangement. Really not anything too difficult, but can be a pain in the butt on some models (depending on access space).

  • It is out of the vehicle. I put the old one back in. The new booster is completely soaked. I also read I could use isopropyl alcohol to clean it out. However, fluid seems to be retained inside an inner chamber that I can't clean. If I plunge the booster, some of the fluid seeps back into the visible area, but I just don't think I can clean this well enough.
    – Josh C.
    Sep 3, 2019 at 18:09
  • 1
    @JoshC. - If you can dilute the brake fluid enough with IPA, the IPA will then evaporate over time and will just be sucked into and burned through the engine without detriment. The way to dilute the brake fluid is to just fill it up with IPA, swish it around some, then drain as much as you can out, through whatever means short of puncturing something. Do this several times. I should then be in pretty good shape. Sep 3, 2019 at 20:34
  • I think the IPA worked. I went through 2 32oz bottles of IPA. I no longer hear a sloshing sound from inside the booster, so I went ahead and installed it. However, I hears a squeak when I release the brake pedal. I wonder if the IPA stripped some of the lubrication from the booster. Is there away I can lubricate it?
    – Josh C.
    Sep 9, 2019 at 1:42

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