MX5 Excessive brake pedal travel when engine is running, pedal is fine when not running, I have changed fluid brakes are bled, hand brake is adjusted properly, I am now think M/C any ideas

Does it have a servo assist on it?

Sounds like it could be leaking vacuum.

Check the callipers before getting involved in stripping the hydraulics.
Look for stuck pads, stuck pistons or sticking guide pins.

If any of the above faults are present the calliper mounting acts like a very stiff spring when the brake is applied.


The way to test a master cylinder is to screw in bleed nipples in place the pipe unions, this should result in an absolutely solid pedal apart from servo lost motion.

Result so far, all calipers are free and working properly, no air in system, pedal comes up with engine off, as soon as it's started the pedal goes to the floor I have taken the vacuum hose off and the pedal is fine, as soon as it's back on the pedal goes to the floor, so dodgy vacuum pump? as there are no leaks on the pipework.