Merry Christmas to all my C10 people...

[c10/72]

Well I'm off to Iraq in two weeks for fifteen months...so my 72 short bed will stay at home under covers for the time being...
Had a question for all my brake experts out there...
I'm using a 8" dual diaphram brake booster with a disc/disc master cylinder and propotioning valve...I've mounted the booster staright to the firewall with no brackets...so its sits flat on the firewall...
My problem is without shiming the master cylinder I have constant brake pressure and cannot move the truck, but when i shim it i cannot keep constant pressure...I've adjusted the rod to the pedal many times and atill nothing...the rod from the booster to the master cylinder is not adjustable...what can I do to use this set-up or do I pay CPP or someone else a ton of money for a new set up? Any ideas would be appreciated...

MERRY CHRISTMAS AND A HAPPY NEW YEAR...