The brakes on my Clio 172 started playing up with a soft pedal. As with master cylinder seals failing a sharp tap on the brake pedal before braking appeared to 'set' the seals and allowed me to brake normally. I've changed the master cylinder (and also a rear brake caliper). However when I start the engine to bleed the brakes I still have a rock hard pedal. Vacuum at the manifold is about 17 inHg and with the servo connected about 15 inHg in line. 15 inHg seems (from what I've read) to be the low end of what is acceptable for a servo vacuum. So I'm wondering if the servo has failed (very rusty down one side) or, if the aftermarked master cylinder is not suitable. I'm now going to swap the new master cylinder for the old and see if that makes a difference.