eNiMaLx Posted January 10, 2022 Share Posted January 10, 2022 Is there a way to determine whether it's the seal of the master cylinder or the secondary cylinder that has failed? Is there also a way to eliminate caliper piston seals from being the culprits? Other than a spongy brake pedal other symptoms are a very hard to retract rear caliper middle piston, and air coming out of the left proportional control valve bleed nipple and the rear caliper middle bleed nipple when attempting to bleed them. The reason I'm confused is that previously the brake pedal still retained its full pressure (for 6000 km since its last service in fact) despite still exhibiting the air bleeding symptom on the secondary cylinder side, making me think that maybe it's normal. On one hand everything seems to point to the secondary cylinder seal, on the other I'm thinking that maybe it's the rear caliper middle piston seal after all. During those 6000 km I rode very hard without realizing that that rear middle piston was sticking. I only realized it after going through new rear brake pads in 6000 km with little to no rear brake use lol, so my reasoning is that maybe the high temperatures and pressures involved from the very hard to retract middle piston coupled with my heavy throttle hand possibly made the seal go bad. Furthermore during the last service I also had to heat the sliding pin with a torch to free the allen bolt, maybe I left the heat on for too long so that also maybe contributed to the seal going bad. In fact after the heating I noticed a lot of rusty brake fluid coming out of the rear caliper during the bleeding procedure, so even though I did my best to flush it out as much as possible with new fluid maybe some remained and further contributed to wearing out the caliper piston seal. All help is greatly appreciated! Link to comment Share on other sites More sharing options...
eNiMaLx Posted April 6, 2022 Author Share Posted April 6, 2022 It turned out to be either the secondary master cylinder seal and/or me bleeding it incorrectly. I ended up following Kev's Shed's procedure to the letter after rebuilding it and the rear brake works perfectly now. Link to comment Share on other sites More sharing options...
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