Allison® 1000/2000/2400 OE C-1 clutch control valve has a fixed flow rate and no seal at the large spool to prevent hot fluid loss. Sonnax C-1 valve and seal kit 37000-05K controls the fill and exhaust rate of the C-1 clutch as well as reducing loss at the valve bore. The regulation contour of the Sonnax valve provides a controlled fill to reduce harsh engagements common to cold weather, long sit or Reverse to Forward abuse conditions. Controlling the flow rate reduces wear on the C-1 clutch hub. Once the valve is open, the C-1 flow is increased over OE to overcome fluid loss at the drum. The valve also has a PTFE seal to prevent incoming pressure loss to exhaust at the pump casting, which can occur under hot abuse conditions.