Got a frantic call from the better half this afternoon to say the brakes on the NB Fairlane had failed. The pedal went to the floor and the brake failure warning light went on. No signs of leaks. When I got home I found that the diaphragm gasket had been put in upside down and had been sucked half way into the master cylinder. There was also signs of leakage from behind the master cylinder (looks like only the fromte clip on the cap was fastened). To be on the safe side, and as there is some sediment in the master cylinder, I going to install a master cylinder kit.
Since I turned the diaphragm gasket the right way up the brakes seem OK and there is no sign of leakage from the wheels or lines (and no significant drop in fluid level. Anyone have a view on the upside down diaphragm being sufficient to cause the brake failure; if so why? I can see that it would stop the diaphragm adjusting for the fluid loss from pad wear and why it would then be sucked down into the master cylinder but even combined with a loose lid why would it cause brake failure (and without warning)? Is it simply that the piston in the cylinder can;t drawn in fluid? If so you would think the pedal would feel stiff or rise slower before the failure as it worked harder to draw fluid from the master cylinder.