* Different Engine Families: The 5.7L Vortec in the Express van is likely a Gen I Vortec, while the 5.3L in the Silverado is a Gen III Vortec. These engines have different bellhousing bolt patterns, meaning the transmission won't physically bolt up.
* Transmission Types: The Express van may have a different transmission type than the Silverado. Even if the bellhousing patterns were compatible, the internal components (like gear ratios) might not match.
* Computer Control: Transmission control systems have evolved. The transmission from the van may not be compatible with the Silverado's computer system and wiring harness.
Here's what you should do instead:
1. Identify the specific transmission: Look up the transmission code on the driver's side of the transmission case.
2. Research compatibility: Use online resources like forums, parts websites, or consult a mechanic to determine if there are any compatible transmissions for your Silverado.
3. Consider a rebuild: If the Silverado's original transmission has issues, it might be more cost-effective to have it rebuilt by a reputable shop.
Important Note: Using the wrong transmission can cause serious problems with your vehicle's performance and reliability. It's best to get expert advice before attempting any transmission swap.