We changed over to a dual line master cylinder about a year ago. The brakes were never that good to start with. But as time goes by the peddal is getting more like pushing on a rock. We changed all the lines with the master cylinder. Is the master cylinder bad?? They are manuel brakes.

Pedal is high and tight but pedal pressure doesn't produce the same braking force as it used to? (& it wasn't that great in the 1st place?) I'd start by opening up each drum & a good basic visual inspection for anything abnormal like contaminated linings.