Master cylinder failed?

[ejparrott]

I'm having trouble with The 109's brakes for the thousandth time, and I'm suspecting master cylinder failure, but a google search of the site the other night found no test for diagnosing.

Couple of months ago the brakes were all bled up to the best they've been for ages, with a new TRW master. They've never been brilliant brakes, but have always passed the MoT. She's been sat for a few weeks, and when I went to use her the other day I've got no brakes at all again. They won't pump up which is making me wonder if the master has gone? Checked the fluid level and its full, no obvious leaks anywhere, is it likely its gone?

[pat_pending]

If the internal seal has gone there'll be no external fluid leak. Try clamping all the flexi hoses, if the m/cyl is ok you'll have a solid pedal, if not it's the m/cyl.

[Phil Hancock]

Sounds like carp under the one way valve, get somebody to push the brake pedal down while you look in the ressy. If the seal is letting the fluid back you will see disturbance in the ressy fluid.

[ejparrott]

I'll have a look when Hol's available to pump it then. Flexi's are stainless so I'm not in a hurry to clamp them, PDWA valve has been removed.

[ejparrott]

Sounds like Ploppy Plop Plops under the one way valve, get somebody to push the brake pedal down while you look in the ressy. If the seal is letting the fluid back you will see disturbance in the ressy fluid.

Hol gave the pedal a damn good pumping tonight and I couldn't see anything like a disturbance in the fluid in the resevoir. Level still hasn't dropped so I don't think there's a leak. Next chance I get I'll put the easibleed on and see if I get a solid pedal.