Hardly any brake pedal after sitting

My truck has been down for roughly 4 weeks while i did my zf6 swap. Got the truck back on the road tuesday and my brakes went to crap. The pedal goes clear to the floor where before it was excellent the only part of the brake system i touched was unbolting the booster to swap pedals. I have checked the system over no leaks anywhere fluid is clear and full. Within 6 months its had all new rear brakes had pads and rotors and a new master cyl and rabs valve put on. Could it have gotten air from sitting never heard of that happening before. i plan to bleed them this weekend but didnt know if there would be somthing else causing this

Did you hook the rod back up?

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^^^ yes, this..

Im not familiar with the swap for parts compatability, but sounds like something was missed and you aren't stroking the MC now. You should not have disturbed the hyd system with that swap.

Yeah its all hooked up