Over recent months my front and rear disc brakes (Hy Rd TRP on my Genesis Croix de Fer) have become increasingly useless, to the extent that I now have to cycle very slowly because it takes at least 5 seconds to stop, regardless of speed, with full pressure on brake.
I won't take you through everything I've done to try and counteract this, but what I did yesterday (without touching it with my oily oily hands) was:
use degreaser on rotors and entire brake area
use sandpaper (quite fine grind) on rotors
change brake pads
tighten brakes and centrally align
and... they're ineffective as ever.
Things I haven't ever done are: bleed brakes (they're hydraulic at bottom and mech at the top), or look at/remove brake cable.
Things I didn't do yesterday: bed in new pads, use isopropryl alcohol rather than degreaser (generic muc off spray).
There hasn't been even a slight improvement in brake power, is it that I didn't get any contaminants off the pads? Didn't bed them in? or something more mechanical that I need to get checked out?