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Newly sprung brake cylinder leak

subpar_bucker

Well Known Member
I'm working through the PAP and after performing the brake testing I noticed a leak inside the plane on the pilot's side. The brakes have been assembled and tested prior. In fact the fuselage had been sitting in my garage for at least 2 years and no leaks. I moved to a hangar about 6 weeks ago (mentioning this because maybe colder temperatures might be a factor). The leak is happening just as the airplane is sitting in the hangar. Yesterday I was able to get a picture showing the leak at the top of the cylinder:

https://photos.app.goo.gl/yfZ6bYnGNz9PSvYt6

Matco's FAQ mentions this leak specifically:

"Question:
Why does my MC-5 master cylinder is leak around the top?

Answer:
Overfilling is the primary reason for leaking around the shaft. Since the master cylinder vents around the shaft, the fluid level should be only 3/4 full to allow for master cylinder travel with the rudder pedals. The MATCO master cylinder is designed to function within fifteen degrees of vertical. If you cannot install within fifteen degrees of vertical, use a remote reservoir master cylinder."

But I'm pretty sure none of those apply to my situation. There are some old VAF posts about leaks springing up here after 100's or 1000's of hours of use, but these brakes are brand new (maybe 100 cycles of testing on them tops).

Has anyone else had a similar issue? I'm wondering if there's a defect with the brake, or if the rebuild kit would fix this issue.
 
When you install the repair kit, double check to make sure the internal snap ring is securely in the groove when on reassembly. Don’t ask how I learned this.
 
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