The origins of force which generate rearward component thrusting begin in the torque converter with converter charge pressure acting on the front face of the input shaft. Typical TH400 converter charge pressure values during high load operation will be in the range of 60 psi with a pressure regulation system capable of producing 180 psi maximum line pressure. Computed out using Pascal’s Law, 60 psi of converter charge pressure acting on the front face of the input shaft generates 47 pounds of rearward thrusting force, or “RTF”, on the forward clutch housing. This however is not the only source of rearward thrusting force on the forward clutch housing. Pressurized lube oil pressure returns thru a passage at the rear end of the pump stator shaft, thru a traverse hole at the rear end of the input shaft, and off to the lubrication circuit. Because the input shaft is pressed into the forward clutch housing, this cooler pressure also acts on the front face of the input shaft boss of the forward clutch housing, generating an additional 152 pounds of RTF, for a total of 199 pounds of RTF on the forward clutch housing. This RTF is then transmitted to the mainshaft at the interface between the forward clutch hub (616), and the mainshaft. This occurs because the front end of the mainshaft acts as a stop for the rear end of the forward clutch hub. From the mainshaft, RTF is transmitted to the rear internal gear (685) and the #22 thrust bearing assembly (686,687,688), then to the output shaft (691) and on to where it is finally grounded out at the transmission case by the output shaft to case thrust and selective washers (695,696). RTF wreaks havoc on the output shaft to case thrust and selective washers. Most seasoned technicians have come across these damaged components at one time or another. In extreme cases it can cause the normally stationary selective washer to spin and tear its locating tabs out of the case, destroying the case thrust surface. Without rerouting or removing RTF in the transmission,which requires specialized components and machining the best the technician can do during an overhaul is take control of RTF by installing this kit.