The open bore of a disc brake caliper assembly is protected by a resilient boot and retainer assembly (92). The piston (38) which forces the friction elements (26, 32) against the friction faces (14, 16) of the rotor (12) is provided with a circumferentially extending groove (118) which receives the bead (96) circumscribing one end of the boot (94). The bead (98) circumscribing the other end of the boot (94) is clamped against a land (122) of the piston 38 by a boot retainer (110). The boot retainer (110) is provided with a radially projecting portion (112) which is held against a circumferentially extending face (108) on the wall of the caliper housing (22) by the oil seal (116). Accordingly, the boot (94) may be removed and a new one installed when the brake is serviced without disassembly of the caliper assembly by withdrawing the piston (38) until the groove (118) is brought into registry with the projection (106), thereby permitting removal of the old boot and installation of a new one.