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-   -   Is this normal? Brake master cylinder 'geyser' (https://www.cherokeeforum.com/f2/normal-brake-master-cylinder-geyser-276047/)

rwmay3 Mar 29, 2026 11:00 PM

Is this normal? Brake master cylinder 'geyser'
 
Per my other thread, chasing a soft brake pedal and suspect it may be my master cylinder, even though I have replaced it, but wonder if it's Chinese junk. Here's a video showing the MC with the cover removed, engine running, and I'm just very slowly and lightly pressing the brake pedal. It shoots brake fluid straight up, making me think the MC isn't pressing fluid down through the system. Just wondering if this is normal? Doesn't seem the seal of the master cylinder cap would bear the full force of the pressure to force the fluid down through the system.


robsjeep Mar 30, 2026 11:41 AM

the reservoir will burp when the brake pedal is released from depressed position. note that the fluid eats paint and will cause corrosion. use soapy water to remove all traces of the spilled fluid. also ALWAYS wear safety glasses with side splash guards. this fluid you dont want in your eye, it burns like hell, like a red hot iron in the eye. got a splash in my eye when flushing the brakes, ran like lightening to a water hose for flushing, still kept burning, had to be taken to ER as it kept burning, very painful experience

exasemech Mar 30, 2026 12:14 PM


Originally Posted by rwmay3 (Post 3737011)
Per my other thread, chasing a soft brake pedal and suspect it may be my master cylinder, even though I have replaced it, but wonder if it's Chinese junk. Here's a video showing the MC with the cover removed, engine running, and I'm just very slowly and lightly pressing the brake pedal. It shoots brake fluid straight up, making me think the MC isn't pressing fluid down through the system. Just wondering if this is normal? Doesn't seem the seal of the master cylinder cap would bear the full force of the pressure to force the fluid down through the system.

https://www.youtube.com/shorts/vUuu7gVXL2U

With all due respect:

You now have 3 threads going on your brake problem,all of which have at least some different information.
Folks may be more inclined to respond if you could consolidate things into one of the three (DON'T start a fourth) and eliminate the others.

rwmay3 Mar 30, 2026 11:18 PM


Originally Posted by robsjeep (Post 3737014)
the reservoir will burp when the brake pedal is released from depressed position. note that the fluid eats paint and will cause corrosion. use soapy water to remove all traces of the spilled fluid. also ALWAYS wear safety glasses with side splash guards. this fluid you dont want in your eye, it burns like hell, like a red hot iron in the eye. got a splash in my eye when flushing the brakes, ran like lightening to a water hose for flushing, still kept burning, had to be taken to ER as it kept burning, very painful experience

Thanks. It actually 'geysers' fluid upon pressing the brake pedal, not releasing it, and I'm just barely pressing it. Seems all the 'force' is going up into the MC instead of down through the lines. Oddly, I do get fluid from all four bleeder screws when bleeding, but with engine on and MC cap off, I get the 'geyser' of fluid going straight up. I'm going to replace the master cylinder (again) with a different brand. Could be the MC I bought was Chinese junk or I've also read you can damage the seals 'jamming' the pedal to the floor after installing the MC....which I may have done.

rwmay3 Mar 30, 2026 11:21 PM

Thanks. Only aware of two threads, one general to the brake system and one trying to draw attention to the oddity of the master cylinder behavior. Hoping someone that knows whether or not it's normal for the MC to shoot fluid upward with the cap off and a gentle light touch of the pedal. I've not seen that specific issue discussed anywhere as a possible symptom of MC seal failure.


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