5|One of the most common problems in a TH350 is a broken accumulator spring. This one is fine but if you find a broken spring in your transmission be sure to inspect the bore. Performance Automatic discards the stock spring and adds an upgraded one. The accumulator spring is designed to cushion the shift. Nusser points out that Performance Automatic doesn’t block off the accumulator spring in street transmissions. Instead it relies on the valvebody modifications to provide firmer shifts.