This valve controls fluid flow to the converter clutch and reduces main line pressure from 255 PSI to 155 PSI when the converter clutch applies, In the LB7 transmission the TRANSGO® A1-LU-BST valve allow the amount of cut-back to be controlled so that main line stays at up to 190 PSI. The LB7 valve will not work on late LLY units. The LLY units require the Sun Coast A1-LU-BST-04 valve for pressure control.