Originally Posted by
timsrv
87 - 89 4wd TV vans with manual transmissions had 2 speed transfer cases. Same year range with auto transmissions had single speed transfer cases. These earlier generation t-cases are physically interchangeable with each other and with the Previa transfer cases. The only problem with putting a manual transfer case on an auto transmission is the input shaft splines (autos & manuals have different spline counts). A cool upgrade for 87 - 89 4wd automatic van owners is to find a t-case from a manual van & install it on their auto transmission. The only hiccup with this swap is the input spline issue. The good news is the input shafts on these TV transfer cases are interchangeable. Since they're removing a single speed transfer case with the correct splines, they can swap input shafts between the two cases & make this mod possible. The 2 speed case is shifted via a separate shifter and cable that is usually taken from the same donor vehicle as the t-case.
This mod can also be done to the automatic Previa except you probably won't be able to swap input shafts. I say "probably" because I'm not aware of anybody who has tried this & don't know if the Previa T-case input shaft is interchangeable with the van T-case shaft (due to the viscous coupling I'm guessing not). There are at least 3 All-Trac Previa owners I know of who have successfully installed a 2 speed transfer case on their manual transmission Previas (without mods). If you were to attempt this on an automatic I would recommend having each flavor of TV transfer case available before starting the project. This will insure you have enough parts (input shafts) to complete the swap. Tim