What you *need* to know to answer this properly:
* What transmission is currently in it (or was originally in it)? This gives a starting point for compatible bolt patterns, bellhousing, and driveshaft length. Common options were the SM465 (4-speed manual), TH350 (3-speed automatic), TH400 (3-speed heavy-duty automatic), and Powerglide (2-speed automatic).
* What engine is in the truck? The engine dictates the bellhousing pattern required. Different engines have different bolt patterns on the flywheel/flexplate. A transmission must match the engine's bellhousing.
* What are your goals? Do you want a stronger transmission? A different number of gears? Better fuel economy? This influences your choices considerably. For example, a 700R4 overdrive automatic would improve fuel economy but needs modification to fit older trucks.
Common Swap Options (with caveats):
* SM465 (4-speed manual): A popular and robust choice, frequently used as a direct swap for existing manuals.
* TH350 (3-speed automatic): Another common option for a relatively straightforward swap.
* TH400 (3-speed heavy-duty automatic): Handles more torque than the TH350.
* 700R4 (4-speed automatic with overdrive): A significant upgrade offering better fuel economy, but requires an adapter or custom modifications to the bellhousing and possibly the driveshaft.
* NV4500 (5-speed manual): A very strong manual transmission, often requiring an adapter.
Important Considerations:
* Bellhousing: This is the critical part that connects the transmission to the engine. You need the correct bellhousing for your engine and transmission combination.
* Driveshaft: The driveshaft length likely needs to be adjusted or replaced when swapping transmissions.
* Crossmember: The transmission crossmember might need to be modified or replaced to accommodate the new transmission.
* Hydraulics: Automatic transmissions require a working hydraulic system.
* Wiring: If installing an automatic with an overdrive, additional wiring may be needed for the electronic controls.
In short: You can't get a definitive answer without providing details about your truck's current setup and your goals. Researching your specific engine and the transmissions compatible with its bellhousing pattern is crucial. A good starting point would be searching online forums dedicated to classic Chevy trucks; experienced owners can provide detailed information based on their own swaps.
