On Tuesday, July 24, 2018 at 11:07:52 AM UTC-4, Charlie Quebec wrote:
Quit so, normal brake fluids are hygroscopic, and easily absorb water, which then causes vapour issues in the lines when heated, allowing it to be compressed.
Sounds to me like dot5 is a better option.

I've forgotten if this was the original problem or not, but I've been through the whole process of rebuilding the hydraulic brake system on a Grob 103.. Complications arise because Grob used an off-the-shelf master cylinder derived from a motorcycle application. That requires a different type of fluid than the usual hydraulic fluid used in aircraft brakes, and expected by the Cleveland wheel cylinder O-ring. One of us went to a mechanic that works on power planes, and he handed us an O-ring based on the Cleveland part number. Then I went to a real glider mechanic, and he threw that one away, because it wasn't going to be compatible. I think we got some help from Robert(?) Mudd, and once you know the material you're looking for, McMaster has them cheap (but you probably have to buy at least 25 to get 1). Unfortunately I've forgotten when that material was, but I could look around in my spare parts box, if it's important to anybody.

I got the master cylinder overhaul parts from a company that supplies parts for old BMW (Oilheads?) motorcycles.

Jim Beckman