Kathy, the clamp that you see soot ( loosen the clamp but do not take it completely off )
Tap on clamp when loose so it moves little up no down. What you are doing is loosen up rust
and carbon soot. Retighten clamp and tap clamp with hammer around clamp as you tighten,
This should make a tight seal. Keith is correct Pac Brake needs a little TLC with little lube
at pivots points and shaft off air push rod. Dave Atherton Retired Cat Mechanic