So I happen to have one each of the following 1967 Buick ST-400 transmissions in my shop: BA - Out of a 1967 GS400 BT - Out of a 1967 Big Car, not sure if it was Electra, Wildcat, or Riviera. BW - Out of a 1967 Sportwagon I know the BT and BW transmissions have the short tail shaft and the BW has the long version. Other than that, what are the differences between, say a BT and a BA transmission? Are the valve bodies physically the same, just calibrated differently for the different car applications? Can you convert a BT transmission to a BA configuration by buying a BA rebuild kit and using it in a BT transmission or is there more to it than that?
The general difference, is the shifts will tend to be harder and possibly at higher rpm, for a heavier car, or for the performance model. Most of this is controlled by the valve body and plate, some in the governor, vac modulator, and pressure regulator. Mods to these are common, I have never seen any factory documentation detailing these. Rebuild kits do not address these details, shift kits do. The 68 up valve bodies are often preferred, as they have another downshift valve. This was apparently left out of the 65-67 to encourage the use of the switch pitch performance mode instead. The good news is that the valve body/plate will interchange on most TH400 years, even with the trans in the car. I always run a later set with the 68 up pan (drain added) and common later filter set. The governor and vacuum modulator allow a lot of trans tuning without dis assembly. Bruce Roe
