With the addition of the six bolt hole oil pump assembly in 1975, some, but not all BCOP transmission case casting changes resulted in a much lighter duty casting, similar to the Chevrolet design. With high output BCOP engines, the 1965 to 1976 BCOP transmission case is heavily reinforced in the bellhousing area, making the use of an aftermarket bellhousing not necessary for most radical drag racing applications. The reinforcement ribs are also found on all Bentley, Jaguar, and Rolls Royce issue TH400 cases.įor Chevrolet engines, the 1965 to 1976 BCOP transmission case, fitted with an aftermarket bellhousing, will deliver the most rigid foundation for assembling a high performance TH400 with a production transmission case. Worthy of noting is that all production Chevrolet cases, whether standard or HD, cases mimicked the light duty casting traits of the BCOP cases. See comparison shown in Figures 13- and 13. Heavy duty BCOP cases were also cast with additional reinforcement ribs/webbing which extends from the rear of the valve body mounting flange to the oil pan mounting flange. Heavy duty BCOP cases were cast with a significantly thicker oil pan mounting flange. Note the reinforced bellhousing area of the heavy-duty casting with its increased material in the bellhousing mounting area and cast reinforcement ribs. The heavy duty BCOP case include several casting benefits that significantly increase the structural rigidity of the component. It is also interesting to note that none of the features of the heavy-duty BCOP case were ever incorporated into any of the Chevrolet castings. The same can be said for the heavy-duty casting. When a BCOP case is referenced in this section as light-duty, the casting is said to include all traits outlined in this section used for comparison with what is said to be a heavy-duty casting.
There were also many “blended” castings which resulted in a case with a combination of features found in both versions. Several light-duty and heavy-versions of the BCOP TH400 transmission case were produced from 1965 thru 1985. The location of the missing lug varies between the 2:00 and 3:00 position. The casting received 17 center support/intermediate clutch backing plate lugs, and plastic vent tube. Note the presence of the mounting bolt hole boss at the 1:00 position with the 1976 Buick case shown in Figure 13. With others, either one or both bolt hole bosses may be present, and when present, may or may not be drilled and tapped. With some cases, the two unused bolt hole bosses were completely removed from the casting. Note the extra material at the 7:00 position of the pump mounting flange with the eight-bolt case in Figure compared to the six-bolt case in Figure.įor the 1975 model year, two of the oil pump mounting bolts previously fit to the transmission case at the 1:00 and 7:00 positions were deleted, along with their thru holes in the oil pump body casting. The casting received 18 center support/intermediate clutch backing plate lugs, and steel vent tube. Because of this, similarities between both groups will be covered first, follow by the features unique to each group.Īll 1965 thru 1974 transmission cases were cast and machined to accept the eight-bolt oil pump assembly. There are design features which are both common and unique to each casting group. The second group is comprised of transmission cases designed to fit Chevrolet engines and is referred to as the Chevrolet casting. The first group is comprised of transmission cases designed to fit Buick, Cadillac, Oldsmobile and Pontiac engines and is referred to as the BCOP casting. The following information will center around the most commonly encountered engine mounting flange configurations which are separated into two groups.
This means the transmission cases were cast with numerous transmission to engine mounting flange configurations. The TH400 has found its way into various vehicle, chassis and engine combinations over the years. Transmission Case Identification and Interchange
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