* Different Bellhousing: Automatic and manual transmissions use different bellhousings, the part that connects the transmission to the engine. You'll need a manual transmission bellhousing.
* Clutch Assembly: You'll need a complete clutch assembly (clutch disc, pressure plate, throw-out bearing, etc.), clutch pedal assembly, linkage or hydraulics, and potentially a new flywheel.
* Driveshaft: The driveshaft length might need to be adjusted or replaced, as manual and automatic transmissions often have different output shaft lengths.
* Crossmember: The transmission crossmember, which supports the transmission, will likely need modification or replacement to accommodate the manual transmission.
* Wiring Harness: The automatic transmission's wiring harness may need modification or replacement to remove components associated with the automatic transmission.
* Shifter: You'll need a manual transmission shifter, linkage, and associated components. The floor will likely need modification to accommodate the shifter.
* Computer Control (Possibly): While less likely on a '78, depending on the engine and options, there may be some computer control aspects of the automatic transmission that will need to be addressed. This will be more involved than simply disconnecting a few wires.
In short: This conversion is a significant project requiring mechanical expertise, specialized tools, and potentially fabrication skills. It's not a job for a beginner. Many mechanics would not undertake such a project because of the extensive modifications and the risk of mistakes. It's far more cost-effective to simply find a car that already has a manual transmission.
