1. Transmission Options:
* 4L60E (TH700R4): This is the most common overdrive transmission used in GM vehicles. It was introduced in the late 1980s, so finding one in good condition for your truck might require some searching. You'll need to adapt the transmission to your existing transfer case, which can be done with an adapter.
* 700R4: This was the earlier version of the 4L60E and might be easier to find, but it's not as durable.
* Other Options: There are other overdrive transmissions available, but compatibility with your truck's engine and drivetrain might be an issue.
2. Rear End Gear Ratio:
* Necessary: Yes, you will almost certainly need to change your rear end gear ratio. Overdrive transmissions decrease engine RPM at highway speeds, which can lead to a sluggish feel and reduced acceleration. A lower rear end gear ratio will compensate for this and improve performance.
* Calculation: The ideal rear end gear ratio depends on your engine size, tire size, and desired driving characteristics. You'll need to research appropriate ratios for your setup.
3. Installation Complexity:
* Significant: Swapping transmissions is a major undertaking that involves:
* Removing the old transmission.
* Adapting the new transmission to your truck's engine and transfer case (may require custom parts or an adapter).
* Potential modifications to the driveshaft and exhaust system.
* Modifying or replacing the engine control module (ECM) to work with the new transmission.
* Professional Help: This is not a project for the faint of heart. It's highly recommended to have a skilled mechanic with experience in these types of conversions perform the work.
4. Additional Considerations:
* Cost: The total cost of the transmission swap, including the new transmission, rear end gears, adapters, and labor can be significant.
* Parts Availability: Sourcing parts, especially for an older truck, may require some effort.
Summary:
While putting an overdrive transmission in your 1981 Chevy truck is feasible, it's not a simple swap. You'll need to consider the transmission options, rear end gear ratio, installation complexity, and costs. Be prepared for a challenging project that requires considerable expertise and resources.
