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SL-00047R1 (brake o-ring replacement)


Well Known Member
I performed this Service Letter about 1 year ago -- replacing the brake O-rings to the U-00025 (Matco-type) o-rings, flushing the fluid and replacing with MIL-PRF-83282 (Royco 782).

Earlier this year, I noticed a slow fluid leak at the reservoir -- initially I thought it was the NPT threads between the reservoir and the "T" (FLF-00004; which btw is missing from KAI Section 4 parts index). So I removed the "T" on the reservoir, cleaned the NPT threads, applied sealant and reassembled. However, it turns out that it was the FLF-00004 "T" fitting itself that was leaking. Small amounts of fluid would get blown by the pilot-side hot air vent and land on the cockpit floor, next to my left heel, along with very minor black/red streaks on the fuselage skin (pilot-side, just aft of the upper cowl).

Since there seems to be little movement between that fitting and the 2 brake lines going to it (F-1289A-L and -R), I do not think the leak was due to mechanical forces on the "T"..

Instead, I was wondering if the o-rings inside the FLF-00004, which apparently are Nitrile (https://www.grainger.com/ec/pdf/19D040_1.pdf) are compatible with the new brake fluid. But from my understanding, nitrile is good with hydraulic fluids.

Has anyone else seen this sort of leak?