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Old 11-30-2022, 12:43 PM
subpar_bucker subpar_bucker is offline
Join Date: Oct 2016
Location: Cranberry Twp, PA
Posts: 73
Default Newly sprung brake cylinder leak

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:

Matco's FAQ mentions this leak specifically:

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

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.
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Old 11-30-2022, 01:46 PM
gasman gasman is offline
Join Date: Mar 2007
Location: Sonoma County
Posts: 4,776

It does not vent around that shaft. The seal is bad and needs to be replaced.
VAF #897 Warren Moretti
2022 =VAF= Dues PAID
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Old 11-30-2022, 04:11 PM
D Weisgerber's Avatar
D Weisgerber D Weisgerber is offline
Join Date: Sep 2019
Location: Ionia Michigan
Posts: 403

Gasman is correct, you're brakes are remote reservoir cylinders.
Dave Weisgerber
RV8 N848DW. Ser#83830 done.
James Cowl
DAR inspection on 7-23-2021
First flight on 7-25-2021
Phase 2 on 9-3-2021
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Old 11-30-2022, 04:40 PM
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PaulvS PaulvS is offline
Join Date: Aug 2019
Location: Western Australia
Posts: 1,326

A repair kit is available from Vans or elsewhere:
Paul vS (yes I'm also a Van)
Building RV-6A #22320 O-320 FP. Wings and tail complete, fuselage almost done, working on canopy.
Flying my Aeroprakt A-22 STOL and the aero club's RV-9A while I build
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Old 11-30-2022, 06:45 PM
subpar_bucker subpar_bucker is offline
Join Date: Oct 2016
Location: Cranberry Twp, PA
Posts: 73

Thanks for the responses! I've already ordered the repair kit.
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Old 11-30-2022, 09:24 PM
N115SB N115SB is offline
Join Date: Mar 2013
Location: Morrilton, AR
Posts: 35

When you install the repair kit, double check to make sure the internal snap ring is securely in the groove when on reassembly. Donít ask how I learned this.
Sheril Helton
Built-Glasair, GlaStar, Rotorway,
2-RV7A's, RV8A, RV10. Built and flying
150hp RV9A.
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Old 12-01-2022, 01:17 AM
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avrojockey avrojockey is offline
Join Date: Aug 2019
Location: Appleton, WI
Posts: 557

Originally Posted by subpar_bucker View Post
Thanks for the responses! I've already ordered the repair kit.
While you're at need to bleed brakes, so accomplishing SL-00047 at the same time and replacing fluid may be in order if not done so already
Tim Holmes
Appleton, WI
RV-9A N904DC
2023 Dues Paid
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