My first mini would suddenly scare the crap out off me, so much so that I would try to drive close to the sidewalk, so wen the brakes just gave out I'd me able to stop lol
Anyway, after many trys at bleeding the brakes simply wouldn't work.
At the mechanic one time, again trying to fix this problem, a mechanic that had just come from Portugal heard me complaining about it and said...."I'll fix it"
what he did....car on the lift, me pouring oil in the reservoir while he bleed the thing.
Never had brake problems after that
Ps: this was a 69 cooper and this is back in 72
Cheers and good luck, Tony

I removed my front drums, slackened the adjusters, and compressed the wheel cylinders all the way. I put a ratchet strap around the shoes and with a power bleeder, I was able to get a few extra air bubbles out of the system. Now the brakes feel amazing! Thanks for your help Alex and Minimans!

Headed to Blackhawk cars and coffee next weekend and hope to see some other minis there!

Do you have a picture of the conical springs? I don't recall ever seeing them. 

I pinched off the lines and pedal is still going to the floor. Got plenty of flow to all the lines and no air coming out anymore. 

All six adjusters have been adjusted properly. I'm definitely thinking the yellow tag master cylinder I installed is faulty. I have another one on the way this week and hopefully it will fix my issue. 

Appreciate the help. Will let you know where I'm at later in the week. -Tim

Have you got the fiddly little conical springs (look like a Lego fir tree) that go between the shoes and the cylinders fitted ?

Without them, the cylinders will retract too far and you'll use up most of the pedal travel getting the cylinders to touch the shoes.

Are all six brake adjusters adjusted properly ?

Wind them in till the wheels won't turn and then check the pedal again.  If you have a decent pedal then you were out of adjustment.  If you still don't have a decent pedal (and the conical springs are fitted) then you've probably still got air in the system.

If you've changed from a dual circuit black tag MC to the later yellow tag, did you check that the unions were the correct ones ?

Black tag Canadian cars were Imperial, everyone else was metric, yellow tag has one of each.

If you've changed from a black tag to a generic MC, did you match the stepped bores ? 

Have you tried pinching off the flex hoses and seeing if you get a pedal? If yes release each hose individually and see where your losing the pedal. Are you getting plenty of fluid from the rears when bleeding? if not then try bleeding the rears very gently on the pedal, the bias valve maybe preventing flow.

I've been fighting a brake problem for a while now and I'm hoping someone here can shed some light on my concern... I acquired my mini a few months back, from Florida. It had been sitting for some time and all but two wheel cylinders were frozen. It's a 76 with 4 wheel drums. I replaced all the wheel cylinders, plus new shoes, bias valve, AP master cylinder(to replace the GMC167), and all lines except for the one that runs from the bias valve to the rear 3-way block. I have bleed the system and have no leaks, no more air coming from the lines. I have adjusted the new shoes all the way around. For some reason my pedal still goes to the floor. I am starting to believe the new master cylinder I installed is defective. I swapped the lines as recommended in the install instructions and kept a board under the pedal while bleeding. What am I missing? I've been a technician for almost 20 years(the last 11 with Aston Martin) and I'm pulling my hair out over this one.