I tried this in the brake forum, but didn't get any conclusive advice, figured I'd try here, as well.

I have a set of Guide RS brakes that fade really badly on long descents. I live in WNC, ride mostly in Pisgah, and by the end of some of the descents, my rear brake is just gone. I can pull the lever all the way to the bar and get very little, whereas at the start it has a normal throw. They don't seem to really improve or go back to normal unless left alone for a fairly extended period of time (several hours) and they don't seem or smell overly hot (I can often smell them when they heat up).

I'm running organic pads, the only thing I haven't tried is swapping to metallic, but no one else I know with organic pads has this issue.

I've bled them with fresh fluid several times, changed out the pads, cleaned the rotors, etc. I don't recall having this problem on any other set of Guides I own, but this is also the first 29er I've had them on, so I don't know if the added wheel weight and leverage on the rotor would cause them to heat up more. I'm also running a 180 in the rear.

Before I invest in a new rotor/pads for the rear, I wanted to see if there was some warranty issue or problem that I wasn't aware of or if anyone had any other suggestions.