brake booster

hey guys, thanks in advance for any and all advice. I have a 74 Roadrunner with rebuilt 440. Got it running, although it seems to be May e have a cylinder misfire. But that's another topic. I am having brake issues at the moment. I have bled the brakes, starting at furthest point, R/R, L/R, R/F...

Another taxi driver and myself replaced my brake booster and master cylinder last summer and it seems we may forgotten to lubricate something. When i am waiting in traffic especially on an incline nose down, and i push on my brakes it sounds like Rubber grabbing. My brakes still work but what...