Here's a breakdown of what's involved:
Challenges and Considerations:
* Transmission Choice: You'll need to find a compatible overdrive transmission. This isn't just about the bolt pattern; you'll need to consider the bellhousing, driveshaft length, and potentially the transfer case (if it's a 4x4). Popular options might include transmissions from later model Chevy trucks, or possibly aftermarket units, but compatibility is crucial. Incorrect choices will lead to significant problems.
* Bellhousing: The bellhousing that connects the transmission to the engine is likely different between your existing transmission and the overdrive unit. You'll probably need a new bellhousing or an adapter.
* Driveshaft: The driveshaft length will almost certainly be wrong. You'll either need a custom driveshaft made or find a used one from a similar year/model truck with the same transmission and rear axle ratio. Getting the driveshaft length wrong can cause vibrations and damage.
* Wiring and Controls: Overdrive transmissions often have electronic controls (shift solenoids, etc.). You may need to add wiring, a shift solenoid, and potentially a computer module to control it properly. This can be complex, especially if you don't have experience with automotive electrical systems.
* Transfer Case (4x4): If your truck is a 4x4, the transfer case compatibility needs careful consideration. It may require modification or replacement.
* Computer/ECU: Depending on the year and options of the donor transmission and your truck's setup, you may need to reprogram or replace your truck's computer module (ECU) to work with the new transmission.
* Mechanic Skills: This is a substantial project requiring a good understanding of automotive mechanics, including transmission removal and installation, driveline components, and potentially electrical systems. It's not a job for a beginner.
Cost:
Expect this to be a costly project. The cost of the transmission itself, plus the bellhousing, driveshaft, potentially the transfer case, and any labor charges if you don't do the work yourself will easily exceed $1000, and can be far more depending on the complexity and parts needed.
In short: While it's *possible*, installing an overdrive transmission in a 1990 Chevy pickup is a challenging and potentially expensive project. It's best suited to someone with significant mechanical experience. Unless you're comfortable with such a repair, it's advisable to seek professional help from a qualified mechanic specializing in transmissions. They can assess the feasibility and give you an accurate estimate of the cost and time involved.
