and chamber 137 the various cavities chambers and passages formed between the mandrel and the housing portions within the jarring tool 10 are filled with an operating fluid such as oil so that the appropriate pressures may be developed static well bore pressure is substantially maintained within chamber 137 by displacement of a balancing piston 152 disposed within the housing portion 20d about the mandrel extension 126 as shown in fig6 the lower annular surface of the balancing piston 152 is exposed to well bore fluid in a sensing chamber 154 which is isolated by the balancing piston 152 from chamber 137 referring to fig7 unrestricted fluid communication is established between lower chamber 154 and the well bore through a port 156 in the mandrel extension 126 the lower axial end of the chamber 154 is otherwise isolated from the well bore by the lower seal portion 30 of the tool carried by the housing portion 20e a spiral flow restrictor 158 is mounted within a shouldered connector portion 160 of the housing 20e to which the housing portion 20d is threadedly connected at 162 the connector section 160 is provided with a recess 164 seating an elastomeric seal element 166 in wiping contact with the mandrel extension 126 the seal element 166 is held assembled between a rigid annular wear ring 168 and a threaded retainer element 170 the lower seal portion 30 fig1 is therefore operative to seal the chamber 154.