240sx Z32 Transmission Swap: 300zx Gearbox Guide

The Nissan 240SX, a beloved platform for drifting and modification, often finds itself needing a stronger transmission than the original unit provides. One popular and relatively straightforward upgrade is swapping in a Z32 300ZX (Twin Turbo or Non-Turbo) gearbox. This article delves into the technical aspects of this swap, providing an in-depth look at the components involved, necessary modifications, and potential pitfalls.

Why the Z32 Transmission?

The Z32 transmission offers several advantages over the stock 240SX unit:

Increased Strength: Z32 transmissions are significantly stronger, capable of handling much more torque, especially the Twin Turbo models. This is critical for modified engines pushing beyond the factory 240SX power levels.
Gear Ratios: While the gear ratios are similar, the Z32 transmissions often have slightly different ratios that can be beneficial depending on the intended use of the car. Careful selection of the correct Z32 transmission (Turbo or Non-Turbo) is crucial to avoid a mismatch.
Availability: Z32 transmissions are generally easier to find and often less expensive than aftermarket high-performance transmissions designed specifically for the 240SX.

Transmission Options: Turbo vs. Non-Turbo

It's vital to understand the differences between the Z32 Turbo and Non-Turbo transmissions. While visually similar, they have key distinctions:

Gear Ratios: As mentioned, the gear ratios differ. The Turbo transmission generally has slightly taller gears, which can be preferable for high-horsepower applications. The Non-Turbo transmission offers shorter ratios, better suited for quicker acceleration. Researching the exact ratios is essential before making a purchase.
Input Shaft: The input shaft length and spline count can differ depending on the engine you're mating it to. This will significantly impact which adapter/clutch setup you can use.
Physical Size: While the bellhousing mating surface is the same, the overall size and shape of the transmissions can vary slightly, potentially affecting fitment in the 240SX transmission tunnel.

Choosing the Right Transmission:

The "right" transmission depends heavily on your specific setup and goals. Consider the following:

Engine Power: For significantly boosted engines, the Turbo transmission is generally recommended due to its increased strength.
Intended Use: For drifting or autocross, shorter gears might be preferable, making the Non-Turbo transmission a viable option. For highway cruising and top-speed runs, the taller Turbo gears might be more suitable.
Budget: Non-Turbo transmissions are often cheaper and easier to source.

Required Components and Modifications

Swapping a Z32 transmission into a 240SX requires more than just bolting it in. Several components and modifications are essential for a successful conversion:

Transmission Adapter Plate: This is arguably the most crucial component. An adapter plate allows you to mate the Z32 transmission to the 240SX's engine (typically an SR20DET or KA24DE). Numerous manufacturers offer adapter plates, each with its own strengths and weaknesses. Carefully research and choose an adapter plate that is known for its quality and precise fitment.
Clutch and Flywheel: The Z32 transmission uses a different clutch and flywheel than the stock 240SX unit. You'll need a clutch and flywheel combination that is compatible with both the Z32 transmission and your engine. Several options exist, including custom-made clutches and flywheels designed specifically for this swap. Consider the power level of your engine when selecting a clutch.
Driveshaft: The Z32 transmission is a different length than the stock 240SX transmission, so you'll need a custom driveshaft. This can be fabricated by a driveshaft shop or purchased from vendors who specialize in 240SX swaps. Measure the required length precisely to ensure proper fitment and minimize vibration.
Shifter Relocation: The Z32 shifter sits in a different location than the 240SX shifter. You'll need a shifter relocation kit to position the shifter properly within the 240SX's interior. Several kits are available, offering varying degrees of adjustability and aesthetics.
Transmission Mount: The Z32 transmission mount is different from the 240SX mount. You'll need to either modify the existing 240SX transmission crossmember or purchase an aftermarket crossmember designed for the Z32 transmission swap.
Speed Sensor: The Z32 speed sensor is different than the 240SX speed sensor. You'll need to either adapt the Z32 speed sensor to work with the 240SX gauge cluster or use an aftermarket speed sensor that is compatible with both. Another option is to use a GPS-based speedometer.
Hydraulic Clutch Line: You may need a custom hydraulic clutch line to connect the Z32 transmission's clutch slave cylinder to the 240SX's clutch master cylinder.
Wiring: Some wiring modifications may be necessary, particularly for the speed sensor.

Step-by-Step Overview (Simplified)

While a detailed, step-by-step instruction manual is beyond the scope of this article, here's a simplified overview of the swap process:

Preparation: Gather all necessary parts, tools, and equipment. Ensure you have a safe and well-lit workspace.
Remove the Stock Transmission: Disconnect the battery, remove the exhaust, driveshaft, and all connections to the stock transmission. Unbolt and remove the transmission from the car.
Install the Adapter Plate: Bolt the adapter plate to the Z32 transmission, ensuring proper alignment.
Install the Flywheel and Clutch: Install the Z32-compatible flywheel and clutch, following the manufacturer's instructions. Torque the flywheel bolts to the specified value.
Install the Transmission: Carefully lift the Z32 transmission into place and bolt it to the engine using the adapter plate.
Install the Transmission Mount: Install the modified or aftermarket transmission crossmember and secure the Z32 transmission mount to it.
Install the Driveshaft: Install the custom driveshaft, ensuring proper alignment and clearance.
Install the Shifter Relocation Kit: Install the shifter relocation kit, following the manufacturer's instructions.
Connect the Hydraulic Clutch Line: Connect the hydraulic clutch line to the Z32 transmission's clutch slave cylinder and the 240SX's clutch master cylinder. Bleed the clutch system.
Connect the Speed Sensor: Connect the speed sensor wiring, adapting it as necessary to work with the 240SX gauge cluster.
Reinstall Remaining Components: Reinstall the exhaust, reconnect the battery, and double-check all connections.
Testing: Start the engine and test the transmission, shifter, and clutch. Check for any leaks or unusual noises.

Potential Challenges and Solutions

The Z32 transmission swap is not without its challenges. Here are some common issues and potential solutions:

Fitment Issues: The Z32 transmission can be a tight fit in the 240SX transmission tunnel. Some minor hammering or trimming of the tunnel may be necessary.
Shifter Position: Getting the shifter position exactly right can be tricky. Fine-tuning the shifter relocation kit is often required.
Vibration: Improper driveshaft length or balance can cause vibration. Ensure the driveshaft is properly measured and balanced.
Clutch Engagement: Proper clutch engagement is crucial. Ensure the clutch master cylinder and slave cylinder are functioning correctly and that the clutch system is properly bled. In some cases, the clutch pedal travel or pivot point might need adjustment.
Speedometer Calibration: Getting the speedometer to read accurately can be challenging. Experiment with different speed sensor adapters or consider using an aftermarket speedometer.

Conclusion

The Z32 transmission swap is a worthwhile upgrade for 240SX owners seeking increased strength and performance. While it requires careful planning, research, and execution, the benefits of a stronger and more reliable transmission can significantly enhance the driving experience. Remember to thoroughly research all components and modifications before starting the swap, and don't hesitate to seek help from experienced mechanics or online forums. Good luck, and happy wrenching!