Brake Failure ?

[yingus]

Hi, i wondered if anyone could advise. I have a 1993 Audi 80 TDI which has been quite a good car apart from niggly little faults. The other day i braked quite hard but only at low speed ( 15 mph ), the brakes worked fine as they should and the anti lock kicked in as it should, after i set off again i slowed to go round a bend and the pedal went straight to the floor with no braking effect at all. I looked around for leaks or obvious broken parts but nothing, i took it home and blead all the breaks, still the same. pumping has no other effects either. If you push the pedal to the floot then press hard there is some slight braking but feel as only 1 or 2 wheels and it locks 1 of the wheels and the antilock kicks in when pressed hard. Someone said maybe the master cylinder but i am not sure, hence the reason i am here asking advice. If it is the master cylinder then 1, Are they hard to take off and replace and 2, where could i get one from. ?

Thankyou.

[yingus]

Hhhmmm, well with hardly any brakes i have not 'really ' used the car, only nipping half a mile to the shop and back now and then, what are left of the brakes where sufficient to stop at slow speed. Anyway i had to go shopping today in the next town and i know it shouldnt have risked it but like a fool i did, which turned out to be good because as soon as i got into the town the brake suddenly started to work again while i was driving, almost threw me out the window because i wasn't expecting it. So now does anyone have a clue what might have gone wrong ? i now have break but refuse to take my family in the car because i don't trust the brakes in case they fail again. Someone please advise, Thanks.