Th-400 need non plastic early type gear retuning 68 trans to stock... Dont get on site often... Best to call: 530-333-3558 or 530-919-5522 scottyb

 

Are you describing the gear on the tail shaft(drive gear) or the one in the housing which connects to the speedo shaft(driven gear)?
For Drive gears contact TCI or one of the many trans shops on line. TCI hepled me out. A local trans shop should have them as well. You will need to know what tooth count. Its much easier to change the drive gear on the tail shaft with the trans out of the car. It is possible to do in the car too. Let me know if you need that guidance
For the driven gear check your local GM dealer or a speedo restoration shop.