Some fluid return through the masters internal ports is normal, and is in fact necessary.
Besides the obvious (calipers, front lines, and m/ cyl) have you upgraded or changed any other components? ( ie: combination/ proportioning valve?)
Did you install a new power booster or adjustable pushrod?
Did you bleed the lines at the master as you were doing them up?
Have you got clean clear (new) fluid at the rear cylinders?
Do you have fluid flow at the new calipers?
Can you find any leaks at your new fittings?
Is your helper pumping the pedal slowly?
Has the master been run dry at any time during the bleeding process?
Are your rear brakes adjusted properly? (improper adjustment at the rear can make the bleeding process damn near impossible!)
If you still have problems after going through all the above, you will need to try a different bleeding process.... similar, but just a couple of new twists....
First you will need to try to "gravity bleed" each wheel individually. Crack the bleeder for one wheel, leave it open until you have some fluid flow through the ******.. repeat for each wheel, then move on to the next step. hint ; leave the lid loose on the master during this part of the process, it will allow gravity to take effect over the system.
Top up the master, and put the lid on ( it doesn't need to be clamped down right now, but it may make it a little less messy if it is...
The procedure is the same, but instead of pumping the pedal and then releasing pressure with the pedal held, you will be cracking the bleeder and then have your helper SLOWLY press the pedal to the floor. Tighten the bleeder, repeat until you have good flow each time the pedal is depressed. Then move on to the next wheel. Make sure to keep the m/ cyl topped up, it doesn't take much to run it dry this way!!
Do the wheels in this order... right rear, left rear, right front, left front....
good luck, let us know how it works out.
