* Electronic Control: The 4L60E is electronically controlled by the vehicle's computer (PCM). The 700R4 is mechanically controlled via a linkage and governor. Your PCM is expecting signals from, and sending signals to, the 4L60E. With a 700R4, it won't receive the expected feedback, leading to:
* Check Engine Light(s): Numerous codes related to transmission operation, likely resulting in limp mode or even preventing the engine from starting.
* Incorrect Shift Points: The PCM will try to control shifts based on its programming for the 4L60E, which won't align with the 700R4's mechanical operation. This can lead to harsh shifts, missed shifts, or engine lugging (overworking the engine).
* Transmission Damage: The incorrect shift points and control could potentially damage the 700R4 itself.
* Torque Converter: The 4L60E and 700R4 use different torque converters. The 700R4 converter won't be properly matched to the engine's characteristics, resulting in poor performance and potential damage to either the converter or the transmission.
* Wiring Harness: You'll need to disconnect and likely modify the wiring harness significantly. Incorrect wiring can damage the PCM or other electrical components.
* Shift Linkage/Cable: You'll need to install a mechanical shift linkage for the 700R4, which your Blazer may not be equipped for. This necessitates modifications to the vehicle's floor pan and potentially the engine compartment.
* TV Cable Adjustment: Crucial for proper transmission operation. Improper adjustment will cause similar issues as described above, potentially damaging the transmission. This needs precise calibration for the 700R4.
* Fluid Pressure: The hydraulic systems of the two transmissions are different. The 700R4's hydraulics and pressure requirements may not be adequately supplied by the 4L60E's pump.
In short, while it's *possible* to do the swap, it's extremely difficult and unlikely to work correctly without extensive modifications and specialized knowledge. It's much more involved than simply bolting on a new transmission. You'd essentially be creating a Frankenstein setup prone to significant reliability issues, potentially resulting in major engine and transmission damage. A much better solution would be a direct replacement 4L60E, a rebuild of the existing 4L60E, or a different, more compatible automatic transmission.
