I have a new customer with a 7FGU35 of the '07 era. It has weak braking. I pulled the wheels and drums today, Everything is in check, wheel cyls move, dry, lots of shoe, no visible wear in drums. good backing plates but still a weak brake. I reassembled it, adjusted it, burnished them a bit but still a crappy brake. BUT the pedal did come up firm. Can those brake valves send a weak or lowered pressure to the cylinders? Anyone run into this before?? I have ordered new shoes because I don't know what OE thickness is.