240sx Transmission Crossmember: Oem Vs. Aftermarket Options

The 240SX, a beloved rear-wheel-drive platform known for its responsiveness and tunability, often finds itself the subject of modifications ranging from mild to wild. One crucial, often overlooked, component in any drivetrain modification is the transmission crossmember. Its job? To securely mount the transmission to the chassis. While the factory (OEM) crossmember serves its purpose for stock applications, swapping in a different transmission or simply pushing the car harder necessitates considering aftermarket options. Let's delve into the world of 240SX transmission crossmembers, comparing OEM versus aftermarket, to help you make an informed decision for your build.

OEM 240SX Transmission Crossmember: Reliable, But Limiting

The original 240SX transmission crossmember is a relatively simple, stamped steel piece. It’s designed to accommodate the factory KA24E/KA24DE (S13) or KA24DE (S14) engines coupled with the stock manual or automatic transmissions. Its primary function is vibration damping and secure mounting, preventing excessive movement and potential damage. Let's break down its pros and cons:

Pros:

Affordable: OEM crossmembers are generally inexpensive, especially if sourced used.
Readily Available: Used OEM crossmembers are easy to find in junkyards or online marketplaces. New, genuine Nissan crossmembers are still available, although often at a higher price point.
Direct Fit: Designed specifically for the 240SX chassis, installation is straightforward and requires no modification (assuming stock transmission).
Vibration Dampening: The stock rubber mounts provide excellent vibration isolation, leading to a quieter and more comfortable ride.

Cons:

Limited Strength: Stamped steel construction isn't ideal for high-horsepower applications or aggressive driving. Over time, it can flex or even crack, particularly around the mounting points.
Transmission Compatibility: Designed specifically for the factory transmissions (FS5W71C, RE4R01A), the OEM crossmember won't work with swapped transmissions without significant modification.
Rubber Mount Degradation: The rubber transmission mount deteriorates over time, especially with exposure to oil, heat, and aggressive driving. This leads to increased drivetrain movement and sloppy shifting.
Ground Clearance: The design of the OEM crossmember can reduce ground clearance, particularly when the car is lowered.

Essentially, the OEM crossmember is adequate for a stock or lightly modified 240SX used primarily for street driving. However, once you start increasing power, swapping transmissions (RB25DET, SR20DET, LS swaps, etc.), or engaging in track days, it becomes a significant weak point in the drivetrain.

Aftermarket 240SX Transmission Crossmembers: Strength and Adaptability

The aftermarket offers a wide array of transmission crossmembers designed to address the limitations of the OEM unit. These are typically constructed from stronger materials and offer greater adjustability and compatibility with various transmission swaps. Here's a look at the common types and their advantages:

Types of Aftermarket Crossmembers:

Reinforced OEM-Style: These are essentially OEM-style crossmembers constructed from thicker gauge steel or reinforced with additional bracing. They retain the OEM mounting points and use factory-style rubber or polyurethane transmission mounts.
Tubular Crossmembers: Constructed from steel tubing, these crossmembers offer increased strength and rigidity while often being lighter than the OEM unit. They typically use polyurethane or solid transmission mounts.
Adjustable Crossmembers: These crossmembers allow for fine-tuning of the transmission's position, which is crucial for achieving proper driveline angles and avoiding vibration issues, especially after lowering the car. They often feature slotted mounting holes or adjustable mounting plates.
Swap-Specific Crossmembers: Designed specifically for popular engine/transmission swap combinations (e.g., SR20DET, RB25DET, LS), these crossmembers ensure proper fitment and driveline geometry for the specific swap.

Advantages of Aftermarket Crossmembers:

Increased Strength and Rigidity: Aftermarket crossmembers, typically constructed from thicker steel or tubular designs, offer significantly improved strength and resistance to flexing, crucial for high-horsepower applications.
Transmission Swap Compatibility: Aftermarket crossmembers are available for a wide range of transmission swaps, eliminating the need for custom fabrication. This saves time, money, and ensures proper fitment.
Improved Driveline Angles: Adjustable crossmembers allow you to correct driveline angles after lowering your car, reducing vibration and preventing premature wear on the U-joints and differential. Driveline angles refer to the angles formed between the transmission output shaft, driveshaft, and differential input shaft. Incorrect driveline angles can cause vibrations and damage to drivetrain components.
Enhanced Ground Clearance: Some aftermarket crossmembers are designed to provide improved ground clearance compared to the OEM unit, which is particularly beneficial for lowered cars.
Polyurethane or Solid Mounts: Many aftermarket crossmembers utilize polyurethane or solid transmission mounts, which offer reduced drivetrain movement and improved shifting feel. However, they also transmit more vibration into the chassis.

Disadvantages of Aftermarket Crossmembers:

Higher Cost: Aftermarket crossmembers are generally more expensive than OEM units. The price can vary depending on the type of crossmember, material, and brand.
Increased NVH (Noise, Vibration, and Harshness): Polyurethane or solid transmission mounts transmit more vibration into the chassis, resulting in a harsher and louder ride. This is a trade-off for improved drivetrain control.
Potential Fitment Issues: While most aftermarket crossmembers are designed for a direct fit, minor fitment issues can sometimes occur, requiring slight adjustments or modifications. Always verify fitment compatibility before purchasing.
Installation Complexity: Some aftermarket crossmembers may require more complex installation procedures than the OEM unit, particularly if they are adjustable or require modifications to the chassis.

Choosing the Right Crossmember: Considerations for Your Build

Selecting the appropriate transmission crossmember depends on your specific needs and goals for your 240SX. Here are some key factors to consider:

Engine and Transmission Combination: Are you running the stock engine and transmission, or have you performed a swap? If you're using a different transmission, you'll need a crossmember specifically designed for that transmission.
Power Level: If you're significantly increasing the power output of your engine, you'll need a stronger crossmember to handle the increased torque.
Driving Style: If you primarily drive on the street, a reinforced OEM-style crossmember with rubber or polyurethane mounts might be sufficient. However, if you frequently track your car or engage in aggressive driving, a tubular or adjustable crossmember with stiffer mounts is recommended.
Suspension Setup: If your car is lowered, you'll need to consider driveline angles and ground clearance. An adjustable crossmember is highly recommended to correct driveline angles and prevent vibration issues.
Budget: Aftermarket crossmembers can range in price from a few hundred dollars to over a thousand dollars. Set a budget and research your options within that range.
NVH Tolerance: Consider how much noise, vibration, and harshness you are willing to tolerate. Polyurethane or solid mounts offer improved performance but at the expense of ride comfort.

Specific Examples:

Stock KA24DE with mild modifications: A reinforced OEM-style crossmember with polyurethane transmission mounts can provide a noticeable improvement in drivetrain stiffness without sacrificing too much comfort.
SR20DET Swap: A swap-specific crossmember designed for the SR20DET and its accompanying transmission is essential for proper fitment and driveline geometry.
RB25DET Swap, lowered suspension: An adjustable crossmember is highly recommended to correct driveline angles and prevent vibration issues. Tubular designs offer excellent strength and clearance.
LS Swap, dedicated track car: A tubular crossmember with solid transmission mounts will provide the ultimate in drivetrain stiffness and control, but will also transmit significant vibration into the chassis.

Conclusion: Upgrade for Performance and Reliability

While the OEM 240SX transmission crossmember is adequate for stock applications, upgrading to an aftermarket unit is a worthwhile investment for anyone seeking to improve the performance, reliability, and longevity of their drivetrain. By carefully considering your specific needs and goals, you can choose the right crossmember to optimize your 240SX for street, track, or drift use. Remember to research different brands and read reviews before making a purchase to ensure you're getting a high-quality product that meets your expectations. Proper installation is crucial, so consider seeking professional assistance if you're not comfortable working on your car's drivetrain. With the right crossmember in place, you can enjoy improved shifting, reduced drivetrain movement, and increased confidence behind the wheel of your 240SX.