This invention relates to braking mechanism for a downhole tool such as a steering tool. The braking mechanism comprises: a body adapted for mounting upon the tool; at least one braking member which is movably mounted upon the body; a resilient biasing means biasing the braking member away from the body; and a damping mechanism connected to the braking member, the damping mechanism providing a damping force opposing movements of the braking member relative to the body, the damping force being dependent upon the rate of movement of the braking member.