sounds like unit to unit variances. My 14' model have fully functional rear Nissin F4 specific 4 piston brake. I thought it had more travel than my Duc's Brembo rear, but that is the way its designed as I found out from Donsy. It works great, just a different initial travel feel, but once that is taken up, it grabs like no tomorrow. Running Motul RBF600 in the system and adjusted the pedal position, now always at the ready for use comfortably. Also with ABS, its a great combo. I understand the talk about heat, but the reality is the rear brake on my Duc get hotter than heck as well as all those components are near exhaust and bolted to nearby components, including the engine block. After riding, I cannot put my hand on the Duc's rear master cylinder. I think if it doesn't work, its more related to moisture in fluid air bubbles, or defective seals.