MG Sports Cars

Just replaced everything on my 73 MGB,Master cylinder,all lines,hoses,calipers rotors,wheel cylinders,shoes,have real good preasure at front calipers,front brakes work great,can't get much preasure going to real drums,not mutch at master cyl. or at rear bleaders,no air,pedal soft for about 2" then nice and hard,bench bled master,gravity bled,odd that the soft feel at first in pedal is front brakes,that work great,then the good firm pedal is when the rear brakes are being applied and not much preasure,can turn rear wheels with brakes on,what about check valves shown in master cyl.can one be sticking,don't know what to do next unless new master cyl.is junk,been a mechanic for 40+ years,never had this issue.

Hey Jack, pull the rear brake line off the master. Screw a plug into the port on the master. Your parts store should have blank plus in stock. And then try the brakes. If you have a good pedal then the master is good.
Next move onto the 4way brake pressure switch. I'm going to guess that this is your problem. The switch, or valve really, is designed to shut off flow to either the front or the rear brakes when it senses a failure. This will trip the warning switch and light up the warning on the dash. You need to re-center the valve. You can do this by opening a front breeder and giving the pedal a stab to turn the light off. Then bleed the rears gently so as not to retrip the valve.
If that's not it, then grab your trusty plug, the one that you didn't throw away after the master tested fine, and plug the rear T one side at a time to isolate each rear brake.
All of that should point you towards the problem. If not hurry up! the lovely Lynne just brought me a Scotchy Scotch so my usefulness is time sensitive. :-)

Live like you mean it.
Fred

Fred,I have a good hard pedal,I did away with the 4 way.valve as I put an 8" Ford drum brake rear in it,I will try the plug trick,a buddy is dropping of his power bleeder tomorrow to try also,thanks for the response.

If you didn't bench bleed the MC before install that is likely your problem.

Jim

so.... you're good and hard, you have 2 inches of travel and no pressure in the rear. but there's no resistance.
We're talking about a car...right? :-)

yeah I know I'm in trouble.

In all seriousness. if the master is solid, it has to be something in the drums.
I would strongly encourage you to install a pressure regulating valve. Without it you simply have a single line system with all of it's failure issues.

Update,I got my buddies power bleeder,put preasure in the system,no air in the rr w/cyl.,went to left side,one little burp of air and I then had rear brakes,must have been somewhere before T on rear end,have good pedal and brakes all around after a manual bleed afterwards,thanks for the help.