A percussion drill rod assembly comprising an elongated inner percussion blow transmitting rod of substantially constant diameter supported in a tubular torque transmitting coupling member by spaced apart sets of resilient isolator members secured to the tubular coupling member. The drill rod assembly is connected to a shank assembly at the drill motor and an adaptor assembly at the bit end, each of which include inner percussion blow transmitting members and outer torque transmitting members. Integral drill rod assemblies having inner percussion rods and outer torque transmitting tubular coupling members are adapted for use with feed leg and sinker drills, for example.
