Wilwood Master Cylinder Issue

[dme922]

I bought a wilwood master cylinder for my 68 k10 and i cannot get fluid to my rear brakes. The MC bench bleads good but after mounting it on the truck i get front but no rear brakes. We have done everything. Push fluid thru the rear lines, changed to an adjustable proportional valve and even got another wilwood mc. That being said i pick up a mc from autozone and had all the brakes. The only difference i can see is the wilwood has a 1 inch bore and the autozone has a 1 1/8 inch bore. Please help.