TH400 fluid drainback

[GRADYS Performance]

Rebuilding the transmission and replacing the torque converter with a remanufactured unit will fix your problem. What has caused the problem would need to be diagnosed during the rebuild and repaired as needed. The front pump would need to be inspected to determine if it needs replaced. It may only need the pump bushing replaced. But you will not know untill the transmission is taken apart. I do not know where you can get a scematic of fluid flow in a TH400.