# T-44587AC Allison LCT1000 Main Shaft Support. Fits 2001-up Silverado HD, Sierra HD.
Prior to final assembly, T-44587AC is installed at the PTO mount, held in place by two bolts. T-44587AC is used to support the main shaft during assembly, providing preload. Why? Once the rear half is assembled and the extension housing is bolted in place, you must roll the trans back over, bellhousing flange up. During this procedure, if not preloaded, the main shaft is able to move. Often, this causes the P3 sun gear thrust bearing to fall out of place. At a minimum, this creates clearance issues costing the time spent disassembling. If gone unnoticed, the bearing gets pinched and self-destructs on the test run, taking out costly hard parts with it.