1. Mechanical Differences and Required Adaptations:
* Length: The 700R4 is significantly longer than the Turbo 350. This necessitates modifications to the driveshaft (likely shortening it) and potentially the crossmember. The driveshaft may need to be balanced after shortening.
* Torque Converter: The 700R4 uses a different torque converter than the Turbo 350. You'll need the correct converter for your application. Incorrect converter choice can lead to poor performance or damage.
* Transmission Mount: The 700R4 requires a different transmission mount.
* Shift Linkage/Cable: The shift linkage or cable is completely different. You'll need a 700R4-specific setup or an aftermarket adapter kit. This is a common source of issues, as getting the linkage adjusted correctly is crucial for smooth shifting.
* Fluid Cooler Lines: The cooler line connections may not match, requiring adaptation or replacement of lines.
* Electrical Connections: The 700R4 is electronically controlled, unlike the simpler mechanical Turbo 350. You might need to address wiring for the transmission's electronic components (speed sensor, kickdown cable/switch). This is particularly important for proper shifting and speedometer function. This often necessitates a wiring harness modification or aftermarket kit.
2. Compatibility Issues:
* Engine: While generally compatible with most small block and big block Chevy engines, there might be compatibility issues with specific engine setups (e.g., aftermarket camshafts might necessitate changes to the torque converter stall speed).
* Rear Axle Ratio: The 700R4's overdrive gear changes the effective gearing. If the rear axle ratio isn't appropriate, you may experience poor fuel economy or acceleration.
* Computer Control (if applicable): The 1986 Silverado might have some form of electronic engine management. Integrating the 700R4's electronics with the existing system might require careful consideration and potentially a tune.
3. Installation Complexity:
* Mechanical Skills: The swap requires significant mechanical knowledge and skills. Incorrect installation can lead to transmission failure or other damage.
* Specialized Tools: Certain tools are required for transmission removal, installation, and adaptation.
4. Cost:
* The 700R4 itself, plus all the necessary adapter components (driveshaft shortening, linkage, etc.), can make this conversion relatively expensive compared to a simple rebuild of the Turbo 350.
In short: While the 700R4 is a desirable upgrade for fuel economy, it's not a straightforward swap. Careful planning, access to the right tools and parts, and a good understanding of automotive mechanics are crucial to a successful conversion. If you lack the expertise, seeking professional assistance from a transmission specialist is highly recommended.
