Converters won't balance (Various KM's and E-CAT converters) Problem : The spring retainters (FIG 1) in the lock up piston assembly are different sized. According to Hyundai engineers, these retainters are the balance weights for the piston assembly, and are selectively placed so that the lock up piston assembly (FIG 2) is individually balanced. If you disassemble the springs and retainers to clean the piston assembly, you run the risk of not putting the different sized retainers back into the same spot.
Solution : Either put the spring retainters back into the same spots, or rebalance the lock up piston (or piston and turbine) as a separate hub assembly.
Spring retainer "pucks" are different sizes. If you completely dissasemble the springs and retainers in order to clean and/or rebond the clutch linings, you need to either put the springs and retainers back into the same locations, or rebalance the complete sub assembly.
KM Style lock up piston. Also note that some units also have intermittent placement of "double" (spring within a spring) dampner springs. Relocation of the double spring could also affect balance characteristics.