Abstract: A method in which the control lockup relay of a “factory installed” A750E, A750F, or A761E automotive transmission is removed from the original valve bore in which it is received, the width of the valve bore in enlarged, and the original control lockup relay is replaced by a wider control lockup relay accommodated in the enlarged valve bore for preventing cross-leaking between an hydraulic circuit applying pressure to the relay and an exhaust to maintain a predetermined applied pressure for normal operation of the relay. The control valve plunger of the lockup control valve of the “factory installed” transmission is replaced by a wider control valve plunger for preventing leaks between the hydraulic circuit applying hydraulic fluid pressure to the lockup control valve and an exhaust for maintaining the hydraulic pressure applied to the lockup control valve above a predetermined pressure for preventing erratic operation of the lockup control valve.