Premature clutch wear in Allison® 1000/2000/2400 ('02-'09) heavy duty applications can occur when the OE valve and spring configuration do not allow TCM pressure control strategy to adequately raise clutch pressure and shorten shift durations. Sonnax trim valve and spring kit 37000-12K alters the A-, B- and F-trim valves and springs, resulting in a more responsive clutch pressure (see Figures 2 and 3).The F-trim bore in '00-'05 units contains an F-trim sleeve (Figure 1). This bore can be upgraded using the spring in this kit and Sonnax F-trim valve sleeve 37000-03.

• Firmer and shorter upshifts
• Firmer TCC engagement
• Improved engine braking on deceleration
• Increased clutch torque capacity