Lude Generation

Pretty sure this is what's at fault but asking here just incase.

Never been to happy with the brakes on the sir (pedal sink). Finally got round to fitting new discs and pads to the rear and decided I may as well fit the braided lines that where meant to go on the 4th.

Everything has been bled up correctly and I'm still getting pedal sink if you stay on the brakes, even had abs kick in now. Switch car off and pump the pedal and brakes firm up again but as soon as car running pedal sinks.

I'm presuming the seals went in the bmc but thought I'd ask to be sure.

Does it not sink when cars switched off at all? If seals have gone in master I would think it would still sink abit when switched off..

yep sounds like master cylinder is on its way out - one or both seals are leaking - bleeding the brakes puts more pressure on them so they just get worse and worse - a new mc is the only option.
you know i had this on my BB4 a few years back - bring the car round and i will be able to tell you if its mc or not