Technical Specifications And Service Guide For The Nissan 240sx Fs5w71c Transmission

The Nissan 240SX, particularly the S13 and S14 chassis, is a beloved platform for modification and motorsports. A key component of its reliability (or sometimes, the source of its headaches) is the FS5W71C manual transmission. This gearbox, used across various Nissan models but most famously paired with the KA24DE engine in the 240SX, is a robust but intricate piece of engineering. This guide delves into the technical specifications and service aspects of the FS5W71C, aimed at enthusiasts and aspiring mechanics seeking a deeper understanding.

General Overview

The FS5W71C is a 5-speed, RWD (Rear-Wheel Drive) manual transmission. The "FS" designates a front-mounted, synchronized transmission. The "5" indicates the number of forward gears. The "W" specifies a wider ratio spread, often found in vehicles designed for both performance and fuel economy. "71C" signifies a specific design evolution and size classification within Nissan's transmission family. While seemingly ubiquitous, there were subtle variations of the FS5W71C depending on the specific model year and application. These variations primarily concerned internal ratios and sometimes minor housing differences.

Key Features:

Fully Synchronized Gears: Synchromesh on all forward gears allows for smooth shifting, even at higher engine speeds. This is a significant advantage over older, non-synchronized transmissions.
Aluminum Alloy Casing: The lightweight aluminum casing helps to reduce overall vehicle weight and improves heat dissipation.
Cable-Operated Shifter: The shifter is connected to the transmission via cables, providing a more precise and direct feel compared to rod-linkage systems.
Removable Bellhousing: The bellhousing, which connects the transmission to the engine, is removable, facilitating easier servicing and compatibility with different engine configurations.

Technical Specifications

Understanding the specifications is crucial for troubleshooting and modifications. Note that these figures can vary slightly depending on the exact model year of your 240SX.

Gear Ratios:

The gear ratios are arguably the most important specification. They determine the relationship between engine speed and wheel speed in each gear.

Here's a common ratio set found in 240SX applications:

1st Gear: 3.321:1

2nd Gear: 1.902:1

3rd Gear: 1.308:1

4th Gear: 1.000:1 (Direct Drive)

5th Gear: 0.838:1 (Overdrive)

Reverse: 3.382:1

These ratios provide a good balance of acceleration in the lower gears and fuel efficiency in the higher gears. The "direct drive" 4th gear means the input shaft and output shaft are rotating at the same speed. The 5th gear acts as an overdrive, allowing the engine to run at a lower RPM for a given speed, improving fuel economy on the highway. However, variations exist across different model years and regions.

Fluid Capacity and Type:

Using the correct fluid is paramount for longevity. Nissan typically specified a GL-4 gear oil. Common options include 75W-90 or 80W-90. Never use GL-5 gear oil as it can damage the brass synchros due to its higher sulfur content.

Fluid Capacity: Approximately 2.6 - 2.8 liters (2.7 - 2.9 quarts)

Regular fluid changes are essential. A good interval is every 30,000 miles under normal driving conditions, or more frequently under demanding usage like racing or drifting.

Torque Capacity:

While no official torque rating exists from Nissan for the FS5W71C in the 240SX application, experienced users estimate it to handle comfortably around 250-300 lb-ft of torque. Exceeding this limit significantly increases the risk of failure, particularly gear stripping or synchro wear.

Dimensions and Weight:

Detailed dimensional drawings are difficult to find, but the transmission is relatively compact. The weight, without fluid, is approximately 80-90 lbs. This can vary slightly based on the inclusion of bellhousing and other components.

Service Guide

Servicing the FS5W71C requires a good understanding of its internal components and proper tools. This section provides a general overview; always consult a repair manual for detailed instructions and safety precautions.

Fluid Change Procedure:

Park the vehicle on a level surface and engage the parking brake.
Allow the transmission to cool down slightly.
Locate the drain and fill plugs on the transmission casing.
Place a drain pan under the drain plug.
Remove the drain plug and allow the old fluid to drain completely.
Reinstall the drain plug with a new crush washer. Torque to the manufacturer's specification (typically around 25-30 lb-ft).
Remove the fill plug.
Using a fluid pump or funnel, add new gear oil until it reaches the bottom of the fill plug hole.
Reinstall the fill plug with a new crush washer. Torque to the manufacturer's specification.
Clean any spilled fluid.
Test drive the vehicle and check for leaks.

Shifter Bushing Replacement:

Worn shifter bushings are a common cause of sloppy shifting. Replacing them can significantly improve the feel and precision of the shifter.

Remove the shift knob and center console.
Disconnect the shifter cables from the transmission.
Remove the shifter assembly from the vehicle.
Inspect the shifter bushings for wear or damage.
Replace the worn bushings with new ones. Polyurethane bushings are a popular upgrade.
Reinstall the shifter assembly and connect the shifter cables.
Adjust the shifter cables as needed to ensure proper gear engagement.
Reinstall the center console and shift knob.

Troubleshooting Common Issues:

Grinding during shifts: Often indicates worn synchros. This requires a transmission rebuild.
Difficulty shifting into gear: Can be caused by worn shifter bushings, damaged shifter cables, low fluid level, or internal transmission problems.
Popping out of gear: Usually indicates worn gear engagement dogs or shift forks. This requires a transmission rebuild.
Excessive noise: Can be caused by worn bearings, damaged gears, or low fluid level.
Fluid leaks: Check the seals around the input shaft, output shaft, and shifter linkages. Replace worn seals as needed.

Rebuilding Considerations:

Rebuilding an FS5W71C is a complex task best left to experienced professionals. It requires specialized tools, knowledge of tolerances, and the ability to properly inspect and replace worn components. However, for ambitious DIYers, a few key points should be considered:

Source a reputable rebuild kit: These kits typically include new synchros, bearings, seals, and other wear items.
Thoroughly clean all components: Before reassembling the transmission, meticulously clean all parts to remove dirt and debris.
Inspect all gears for wear or damage: Pay close attention to the gear teeth and engagement dogs. Replace any gears that show signs of wear or damage.
Use the correct torque specifications: Adhering to the manufacturer's torque specifications is crucial to prevent damage to the transmission.
Pay close attention to clearances and shimming: Proper clearances and shimming are essential for ensuring smooth and reliable operation.

Upgrades and Modifications

For those seeking more performance from their FS5W71C, several upgrades and modifications are available:

Short Shifter Kits: Reduce the throw of the shifter for faster and more precise shifts.
Performance Clutch Kits: Provide increased clamping force for higher horsepower applications.
Steel Shift Forks: Stronger than the factory aluminum shift forks, these can withstand higher loads and prevent bending or breakage.
Gear Ratio Changes: While less common, altering the gear ratios can optimize the transmission for specific driving conditions.
Oil Cooler: For high-performance applications, an oil cooler can help to reduce transmission temperatures and prolong its lifespan.

Conclusion

The Nissan 240SX FS5W71C transmission is a durable and well-engineered unit, capable of providing years of reliable service with proper maintenance. Understanding its specifications, service procedures, and potential upgrades is essential for any 240SX enthusiast. While complex, a basic understanding of its operation empowers enthusiasts to maintain, troubleshoot, and even modify their transmission for improved performance and longevity. Remember to always prioritize safety and consult a qualified mechanic when performing any major repairs or modifications.