Allison 1000/2000/2400 Trim Valve & Spring KitTranstar now carries the Trim Valves and Springs Kit for the Allison 1000, 2000, and 2400 series transmissions years 2002 and up. This Sonnax kit (37000-12K) addresses the issue of long shift duration which promotes premature clutch wear in heavy-duty applications. The kit includes A trim valve and spring, B trim valve and spring, and F trim spring. To use this kit, the valve body must be modified by using Transtar Part No. T-37000-TL12 (Sonnax Part No. 37000-TL12) which includes reamers for the A and B trim valve bores.