A yaw brake for a wind turbine, comprising: a caliper body defining first and second jaws (54, 56) configured to be disposed on opposite sides of a brake disc disposed about a yaw axis, the caliper body defining a bore in one of the first and second jaws (54, 56); a brake pad configured for movement relative to the caliper body between a first position in which the brake pad applies a first braking force to the brake disc and a second position in which the brake pad applies a second braking force to the brake disc, the second braking force greater than the first braking force; and, a piston (52, 80) disposed within the bore of the caliper body and configured for movement within the bore along a first axis (66, 86) to cause movement of the brake pad between the first position and the second position and the piston (52, 80) includes a body (68, 82) defining a crown (72, 90) facing the brake pad, the body (68, 82) made from a first material; and, a deformable member (70, 84) configured for mounting on the body (68, 82) characterized in that the deformable member (70 or 84) is radially aligned with the crown (72 or 90) of the body (68 or 82) and not disposed between the crown (72 or 90) and the brake pad in the direction of the first axis (66 or 86), the deformable member (70, 84) is made from a second material having a lower hardness than the first material and configured to assume a first form when the brake pad is in the first position and a second form when the brake pad is in the second position, the deformable member (70, 84) defining an end face (78, 92) facing the brake pad and nearer to the brake pad than the crown (72, 90) when the brake pad is in the first position. a caliper body defining first and second jaws (54, 56) configured to be disposed on opposite sides of a brake disc disposed about a yaw axis, the caliper body defining a bore in one of the first and second jaws (54, 56); a brake pad configured for movement relative to the caliper body between a first position in which the brake pad applies a first braking force to the brake disc and a second position in which the brake pad applies a second braking force to the brake disc, the second braking force greater than the first braking force; and, a piston (52, 80) disposed within the bore of the caliper body and configured for movement within the bore along a first axis (66, 86) to cause movement of the brake pad between the first position and the second position and the piston (52, 80) includes a body (68, 82) defining a crown (72, 90) facing the brake pad, the body (68, 82) made from a first material; and, a deformable member (70, 84) configured for mounting on the body (68, 82) characterized in that the deformable member (70 or 84) is radially aligned with the crown (72 or 90) of the body (68 or 82) and not disposed between the crown (72 or 90) and the brake pad in the direction of the first axis (66 or 86), the deformable member (70, 84) is made from a second material having a lower hardness than the first material and configured to assume a first form when the brake pad is in the first position and a second form when the brake pad is in the second position, the deformable member (70, 84) defining an end face (78, 92) facing the brake pad and nearer to the brake pad than the crown (72, 90) when the brake pad is in the first position.