* Different Bolt Patterns: While the overall dimensions might seem similar, the bellhousing bolt patterns are different. You'll need a 700R4-compatible bellhousing or adapt the existing one, which is a machining job best left to a transmission specialist.
* Length: The 700R4 is generally shorter than the TH400. This means your driveshaft will likely need to be shortened.
* Crossmember: The transmission mount location will be different, requiring modification or replacement of the crossmember.
* Torque Converter: The torque converters are not interchangeable. You'll need a 700R4 torque converter.
* Computer Control: The 700R4 is electronically controlled, unlike the TH400 which is purely mechanical. This means you'll need to integrate the 700R4's control system into your vehicle's electrical system. This often requires a custom wiring harness, a computer capable of controlling the transmission (possibly a standalone unit or modifications to your existing ECU), and potentially a transmission controller. This is a complex undertaking, especially for older vehicles not originally equipped for electronic control.
* Cooling: The 700R4 requires a transmission cooler, which the TH400 might not have had, or might have a cooler insufficient for the 700R4.
* Shift Linkage: The linkage or cable setup will need to be completely changed to accommodate the 700R4's shifting mechanism.
In short, while physically possible, swapping a 700R4 for a TH400 is a major undertaking requiring specialized knowledge and tools. It's not a simple swap for the average mechanic and is best left to a professional transmission shop experienced with this specific conversion. The cost of parts and labor could easily exceed the cost of a rebuilt TH400. Consider carefully if the benefits outweigh the significant time, effort, and expense.
