The manual shifter shaft seal on the TH425 transmission is different than most other Turbo-Hydramatic transmissions. It is an O-ring shown on this diagram as item 9. Manny told me that many transmission shops don't replace it because they don't know its there!
To replace the O-ring you must:
-Drop the pan
-Remove the detent roller spring (item 8)
-Remove the bolt holding the gear selector detent cam
-Pull a roll pin which goes up into the transmission case alongside the shaft. Use a pair of vice grips to grasp the pin and pull downward (thanks Manny for the tip!)
Then the shifter shaft can be pulled out. The O-ring is on the shaft. Mine was hard and crumbled when I removed it. An oil resistant O-ring can be used as a replacement.
From Manny, the O-ring is: A012 9.25x1.78mm (0.364"ID x 0.500" OD x 0.070") crosses to Spaenaur Nitrile 318-A08-1X
To replace the O-ring you must:
-Drop the pan
-Remove the detent roller spring (item 8)
-Remove the bolt holding the gear selector detent cam
-Pull a roll pin which goes up into the transmission case alongside the shaft. Use a pair of vice grips to grasp the pin and pull downward (thanks Manny for the tip!)
Then the shifter shaft can be pulled out. The O-ring is on the shaft. Mine was hard and crumbled when I removed it. An oil resistant O-ring can be used as a replacement.
From Manny, the O-ring is: A012 9.25x1.78mm (0.364"ID x 0.500" OD x 0.070") crosses to Spaenaur Nitrile 318-A08-1X
