The aim of this work is to develop a viscous braking system using magneto rheological fluid  (MR fluid) that has performance advantages over the conventional hydraulic braking system. The proposed braking system consists of rotating disks immersed in a MR fluid and enclosed in an electromagnet, which the yield stress of the fluid varies as a function of the magnetic field applied by the electromagnet. The controllable yield stress causes friction on the rotating disk surfaces, thus generating a retarding brake torque. The braking torque can be precisely controlled by changing the current applied t o the electromagnet.