* Mechanical incompatibility: The engine, transmission, and drivetrain components are designed to work together. A manual transmission requires a different clutch system, shifter, and linkage, and it interacts with the engine differently than an automatic transmission.
* Computer systems: Modern cars have sophisticated computer systems that control the engine, transmission, and other components. These systems are designed for the specific type of transmission the car was built with. Installing a manual transmission would likely cause major conflicts with the computer systems.
* Physical space: The engine compartment and transmission tunnel are often designed with a specific transmission in mind. A manual transmission may not physically fit or may require significant modifications to the car's structure.
* Wiring and plumbing: The wiring harness and hydraulic lines for an automatic transmission are different from those for a manual transmission. You would need to completely rewire and re-plumb the car.
It's not impossible, but it's extremely difficult and expensive. The amount of work required would be significant, including:
* Replacing the entire transmission and associated components.
* Modifying the engine or engine control unit to work with a manual transmission.
* Rewiring the car and potentially modifying the dashboard.
* Adapting the drive shaft and rear axle.
* Significant body work to accommodate the new transmission.
In most cases, it's simply not practical or cost-effective to convert an automatic car to a manual. It's usually easier and cheaper to find a car that already has the type of transmission you want.
