I have a problem with my brakes just got them all hooked up stanza disk front bluebird disk rear 3/4 master cylinder on 12y booster back bracks are coming on but the front won't .I have disconnected the rear, the front works then ???? The front is working when the system is all conected you just can't push the pedal hard enough to get the front to stop turning

is the master cylinder from a drum brake rear car? if so it will have a proportioning valve in it, or somewhere in the stock 1200 brake lines, meaning more pressure is put to the rear of the vehicle as the drum brakes took a bit more to get them to bite in before the front disks.
thats what i think it sounds like

It is a brake balance problem. The rears need limited pressure to solve this problem.

Was the master cylinder designed for all-disk brakes?

The car the brake booster and master cylinder came off had drum rear brakes

I don't think it is maybee that complicated,but first i have to ask a (maybee) silly question.
Are the bleeders on the front calipers at the top(don't laugh it's a common mistake)
Now put a brake hose clamp on the rear flexable hose on the diff housing.Start by bleeding the master cylinder(disconnect the vacuum hose to the booster)continue till your happy all the air is purged,now move to the front calipers and do the same,it can take some time to get all the air out when starting from scratch.If all is as it should be you should start to get a pedal,once you do remove the brake hose clamp down the back.By using this method you are isolating each end and if there are further problems you know which end to chase.
Enjoy
Cheers

Right, good idea. Check the basics first.

yes the bleeders are on the top both front and back I bled the front with the rear blocked at the master cylinder then connected the rear and bled it the peddle then stopped the rear but I could still turn the front

This is all quite curious,remember pressure will be equal in all directions..only volume will be differant.How have you managed to isolate the rear brakes at the master cylinder without exposing the lines to atmosphere or do you have rubber lines at this point.
Another silly question,is the front brake line going into the master cylinder at the outlet nearest the firewall and the rear brakes nearest the front of the car on the M/C.

What does the pedal feel like,progressive,a clicky feel half way down?

while where on the subject about rear brakes, should you or not have one of these (splitter) for the balance when running rear disc's
or is it not needed?

That is not needed.

It does two things:
1. Splits the two lines in to four lines out
2. Has a pressure switch. It doesn't change the pressure, but if front and rear don't have similar pressure, it lights a lamp on the dash.

Since he is mixing/matching brakes front/rear, he probably needs a proportioning valves. Volvos and race cars use them.


On a stocker, the proportion front/rear is establish by careful selection of brake cylinder sizes. For example, on a disc-brake 1200, the rear cylinders are a different size than on a front-drum 1200. Nissan carefully chose the right sizes to achieve the right proportion. On a home-picked brake system, a proportioning valve can be used to adjust it manually.