MGB: 1970MGB GT Brakes

1970 MGB GT new master cylinder; new rubber hoses front & back; rebuilt calipers, rebuilt wheel cylinders; flushed lines. I can not get the system to bleed! It is like the MC is not pumping. It pushes are on the bench, I have bleed the lines at fittings. tried pressure bleeding, reverse bleeding, Never had brake problems like this before. Any advise?

New parts aren't always good parts. Sounds like a defective MC.

Well I thought the same and did not think it was pumping. So I disassembled the MC and rebuilt it. It had some crud around the resovour seals, I clean the ports to the cylinder, and it seemed to be pushing air from both ports. I have it mounted and it only pushes air though the front port but will not pump up. I am sumped this has never happened before to me.

did you rebuild this piecce or did you buy it rebuilt/new (before you took it apart again, thus voiding any warranty that might have been on it)?

easy to bench bleed a MC. if it has fluid and you can't pump fluid out of it then I'd say it is assembled wrong or the cups or bores are worn.

if it pumps fluid on the bench, hook it back up and "push bleed" it. push fluid IN from the rear cylinders then from the calipers. empty the MC before you start pushing it in. as soon as some fluid (just a little is all you need) appears in the MC, you're done with that wheel. when all 4 are done, top off to proper level.

When you pump up the brakes to bleed, the action has to be a slow pump. Rapid pumping will introduce air to the system. Each time you open and close a wheel cylinder you should also wait about 10seconds before repeating the process. This allows the air bubbles to come to the top.
Also when bench bleeding you can make little plugs with a small bolt and a piece of the right size vacuum hose to keep the fluid from leaking out the fittings while mounting the M/C.