i have a th 400 i just got for my 81 blazer out of some type of older car 2 wheel drive i am not sure what. i want to put a devorced 203 trans case in but i can not find the correct filter for my th 400. it has the 13 bolt pattern but the filters for the 400 do not fit it. I have tried finding the codes for it online with no luck can anyone explain what the hell alien trans i have???

 

TH400s were made in a couple of different versions, so knowing the year of the transmission is important to facilitate your being able to swap it into your car easily. The first-generation units were only used in Buick, Olds, and Cadillac, and incorporated a variable-pitch torque converter. This converter could change its stall speed during use, based on an electrical impulse from a switch on the carburetor or accelerator pedal sent to a two-prong switch in the side of the transmission. This variable-pitch version of the TH400 was only used from 1965 to mid-1967. Later units had a fixed-pitch converter and had a one-prong switch, the two-prong "pitch switch" was not used.

Another way to identify the early variable-pitch units is by the transmission pan. The earlier pans were identical in shape to the later pans, and all used the same 13-bolt hole pattern; however, the variable-pitch transmissions had four indentations in the pan (one large oval-shaped indentation as well as three small "dimples" around it). The late-1967 and up transmissions used a pan with only two small "dimples" in it. If the pan is not on the transmission, the early filter had an intake pipe attached to it and could be washed and re-used. The later filter was flatter with no intake pipe, and was a throwaway unit. All TH400s used a large black can-type vacuum modulator located on the side of the transmission by the dipstick tube. When you find a transmission for a car newer than 1968, the vehicle's original VIN number will be stamped on the casing. So that would be yet another way to ensure the transmission is not a variable-pitch unit