4R100 PWM units use a plunger valve assembly and coil spring to cushion the TCC control valve. That assembly uses regulated converter pressure as a variable hydraulic spring to control the rate of TCC apply. Continuous oscillation of the TCC control plunger valve wears the sleeve ID, allowing regulated converter pressure leakage. This can result in premature or bumpy TCC apply and/or shudder. Sonnax offers a drop-in replacement assembly, 36424-08K.