Valves do come in different diameters, some require modifying the valve body on a mill. Some of the pro tree brakes use fluid to release the valve and some use a spring. The ones with a spring need a fairly stiff spring, as long as the solenoid has enough power to compress it a stronger one won't hurt. Also if the solenoid is a 1 wire, make sure you run a ground from the battery to the trans to make sure you have a good ground there.