I blew out my left brake the other day. Apparently the o-ring let go, because a few days later, I returned to my hanger to find a trail of hydraulic fluid on the hanger floor. I removed the caliper, and found evidence of fluid around the piston margins and on the disc and pads, but no extruded o-ring. Anyway, I removed the piston and found some mild scoring on the side of the piston that was easily sanded off, and no damage to the cylinder. There was a very small amount of dirt/debris in the residual fluid. What was interesting was the o-ring - which didn't look particularly damaged - but was almost perfectly square in profile and seemed to fill the seat in the piston (the new one is round.) My question is: will an o-ring take on a square profile once installed and in service, or is this clearly an incorrect part? I also found that the pressure plate is slightly warped (which I cannot pound out,) and a previous owner or builder did a bad job drilling out old rivets (two of three are oblong.) Could this have caused the brake failure?
Related to this thread is the reservoir. Mine is installed on the engine side of the firewall, with a fairly long run of clear tubing forming the low pressure supply side of the system. I can clearly see that the left channel is empty of fluid, but the right side also has air in it - trapped in a high area underneath the baggage floor between the master cylinders and the adel clamps under the rear bulkhead of the baggage compartment. I just ordered the Matco individual reservoirs - I don't like the idea of any air in the system.