So I have sort of a headscratcher that hopefully you guys can help me with. I installed a new brembo rcs17 onto my abs rsv4 yesterday. Install went smoothly and was able to bleed the system without issue. Went for a test ride afterwards and the brakes felt great. Threw a zip tie on the lever overnight to hopefully get a little extra firmness. When I came out in the morning the lever was completely soft. I removed the zip tie and on the first pull the lever got firm again. I re-bled the brakes just in case there was some air in the system. Zip tied it again and same issue with soft lever after removing zip tie. Checked everything for leaks and everything was nice and dry. If my understanding of how the system works is correct, there should be no way that the lever could loose pressure overnight short of a leak somewhere in system (either internally or externally). If there are no external leaks is it safe to conclude that the pressure leaked back into the reservoir? Would this point to a faulty seal in the master? I have bled and zip tied many other masters and never recall the levers being soft after removing the zip tie.
I experienced two failed RCS master cylinders out of the box this year. I would try to exchange it if I were you.
Mine suffered from similar symptoms. Complete loss of pressure and instant pressure if the lever was pulled again, almost ran over a corner worker. Scared the crap out of both of us.
Thanks for the replies, my thought was that the only way it could be losing pressure with the lever pulled(short of an external leak) would be if the mc seals were leaking the pressure back into the reservoir any luck getting it warrantied by brembo?
Didn't even try, it had a few weekends on it so I just threw it out. Before the sudden failure it had a very small parasitic leak just like yours so I never really trusted it. I just assumed it was a defect.
Do you still have ABS? You need to activate the ABS to bleed the brakes. You didn't say what year your RSV4 is, but I know thats how it was on the earlier bikes. Mine was a 2014.
