Abstract: A brake unit having a hydrodynamic retarder providing brake torque proportional to speed and inlet pressure, and a friction brake providing brake torque proportional to net brake pressure, the brake apply pressure minus retarder inlet pressure. The controls have a brake demand valve providing a brake demand pressure. A retarder valve is biased by brake demand pressure from brake-off position to brake-on position for switching the retarder circuit to fill the retarder and to connect low and high speed regulator valves to regulate retarder inlet pressure respectively to increase in the low speed range and to decrease in the high speed range with increasing speed, and to limit retarder inlet pressure proportionally to brake demand. The controls, in the low speed range, provide friction brake apply pressure proportional to brake demand, so the friction brake net apply pressure and torque decrease to zero and retarder torque increases as speed increases.