scuffed master cylinder

[kjlpdx]

my R Cleveland master brake cylinder was scuffed, the piston especially, so it was not working very well. I have replaced it with a Matco. in talking with Rian at Vans he mentioned that this isn't an uncommon problem. he noted that on his BMW they tell you to only bleed brakes using a vacuum at the wheel and not push the fluid up the line. I have pushed fluid up the line for years. my plane has always pulled left because I believe the nose gear wasn't drilled correctly to begin with. consequentially I have worked on the right brake many times over the years and replaced the rotor even. Rian thinks, and after disassembly and inspection I agree with him, that pushing the brake fluid up the line pumps any burnt fluid and gunk up into the master and reserve tank. so I bought a vacuum pump, HF $23, and sucked the fluid down this time. the pump has a tank that collects what is pulled down. it was noticeably darker than the new fluid. there also were black specks in the cylinder when I took it apart. we'll see how the next 1400 hrs goes!

[cdeerinck]

Very helpful post. Thank you!

[Ralph Inkster]

Dirty fluid probably doesn't help matters, but my theory for scuffing pistons is the way the m/cyl is mounted. The offset bolt arrangement in my view causes a side loading of the rod (plunger) as foot pressure is applied and eventual scuffing results. Maybe how tight the mounting bolts are set is a contributing factor as well, looser or floppier the m/cyl is the more likely to scuff??
I've replaced a few on various RVs & accept that these are eventual maintenance items.

[flyingriki]

Fluid should be changed periodically. Here Dick says this at minute 3:20

http://www.eaavideo.org/video.aspx?v=2520200703001

http://bcove.me/2pw4q9fe