[Cliff R]

TH400's come in several flavors. Long and short tailshaft for starters. The short tail units are usually prefered for mid size cars. Internally there were some changes thru the years of production. Very early units use two sprag clutches, then a roller clutch replaced the low sprag. In the early 70's a roller clutch replaced the int. sprag. The low roller clutch is fine as it is not involved in a shift. The int. roller clutch can/will fail in an hp application. Even the early style int sprag only has around 11 elements and upgrading to the 34 element is manditory for serious use. There were also several planetary sets offered, some units use straight cut teeth, most are helical. Steel apply pistons will be found in some units vs aluminum. You will also find some stamped steel parts and telfon sealing rings in later transmissions.

Nearly every different model of TH400 used different clutch pack arrangements. Generally speaking the heavy duty and high performance units got more clutches. You can purchase the shorter apply pistons to increase clutch capacity during rebuilding.

It is a good idea to pick up 60's era TH400's even if they are the long tailshaft version. The direct drum will accept the 34 element sprag and save some money during rebuilding. The later direct drums with roller clutches will not accept a sprag type clutch. Most parts will interchange thru the years of production, however there are some minor differences in the pumps and other hard parts so great care must be taken during mixing/matching. For example, the check ball can be found in either the drum or the piston, but is not used in both.

Don't have much info as to how to identify them? Nearly as I can remember the early units use more bolts to hold the pump. Hope the info helps some....Cliff