[Cliff R]

If you are going to use teflon rings, obtain them for the 4L80 transmission, they are solid instead of scarf cut. You will also need the correct tools to install them. The iron rings are easier to install and a better choice in my opinion. 98-up 4L80 units use plastic rings that snap together. Haven't tried any yet in a TH400, but it's tempting. I still use the hooked iron rings, they're old school, but they work.

Replace all the bushings during rebuilding no matter how good they look, same for the thrust washers. By minimizing up/down fore/aft play the trans will seal up better and run quieter after it is placed in service, aside from lasting about 10 times as long.

Air pressure check all of the drums before installation, then again after the trans is together. If you have any troubles with sealing rings or piston seals, it will be evident during the air pressure check. Do not put a unit into service that shows any leakage during the pressure check. This step is left out during most home builds. If you can apply the low band and the three clutch packs on the bench, it will short cut troubleshooting if you have problems once the unit is placed in service.....Cliff