Auto To Manual Conversion Kit

Converting an automatic transmission car to a manual transmission is a significant undertaking, often driven by a desire for enhanced driving experience, improved fuel economy (though debatable on modern automatics), or increased control for performance applications. While a complete factory-like conversion is ideal, many opt for auto-to-manual conversion kits to simplify the process. This article will delve into the maintenance, troubleshooting, and real-world issues associated with using these kits, offering practical advice for both car owners and mechanics.

Understanding Auto-to-Manual Conversion Kits

Auto-to-manual conversion kits typically include the essential components needed to replace the automatic transmission with a manual one. These commonly include:

• Manual transmission itself (often remanufactured or aftermarket).
• Clutch assembly (disc, pressure plate, throwout bearing).
• Flywheel (crucial for mounting the clutch).
• Shifter assembly (shifter, linkage, knob).
• Pedal assembly (clutch, brake, sometimes accelerator depending on application).
• Hydraulic or cable clutch system components (master cylinder, slave cylinder, lines, or cables).
• Possibly a modified driveshaft or adapter to fit the new transmission.
• Wiring harness modifications or adapters for neutral safety switch and reverse lights.
• Sometimes, a new ECU or a tune for the existing ECU to accommodate the manual transmission.

While these kits aim to streamline the conversion, it's essential to understand that they are not always "plug-and-play." Modifications and adjustments are often necessary, and the quality of the components significantly impacts long-term reliability.

Maintenance After Conversion

Once the conversion is complete, regular maintenance is critical to ensure the longevity of the new manual transmission. Here are some key areas to focus on:

Transmission Fluid

Symptom: Difficult shifting, grinding noises, transmission whine.

Cause: Low, contaminated, or incorrect transmission fluid.

Solution: Regularly check the transmission fluid level and condition. Follow the manufacturer's recommendations for fluid type and change intervals. Use a high-quality synthetic fluid for enhanced performance and protection. For example, on a converted Honda Civic using a kit with a B-series transmission, using Honda MTF or a comparable synthetic blend is essential. Over time, the fluid degrades and loses its lubricating properties. Debris from wear and tear can contaminate the fluid, leading to increased friction and wear on the gears and synchronizers. A complete fluid flush is recommended at the specified intervals.

Clutch System

Symptom: Clutch slippage, difficulty engaging gears, noisy clutch operation.

Cause: Worn clutch disc, faulty pressure plate, worn or leaking clutch master or slave cylinder (if hydraulic), stretched or binding clutch cable (if cable-operated).

Solution: Regularly inspect the clutch pedal free play and adjust as needed. If the clutch is slipping (engine RPM increases without a corresponding increase in vehicle speed), it likely needs replacement. For hydraulic systems, check for leaks around the master and slave cylinders. Bleed the clutch hydraulic system periodically to remove air bubbles, which can cause spongy pedal feel and poor clutch engagement. A common issue on converted Mazda Miatas is clutch slave cylinder failure, especially when using aftermarket kits. Inspecting and replacing the slave cylinder proactively can prevent unexpected breakdowns. Also, consider upgrading to a higher-performance clutch kit if you plan on increased engine output.

Shifter Linkage

Symptom: Sloppy or vague shifting, difficulty finding gears.

Cause: Worn or loose shifter bushings, misaligned shifter linkage.

Solution: Inspect the shifter bushings for wear and replace them as needed. Many aftermarket shifter bushings are available that offer improved precision and durability. Adjust the shifter linkage to ensure proper alignment and engagement of gears. On vehicles like converted Mustangs, the shifter linkage can be particularly susceptible to wear due to the added stress of aggressive shifting. Consider upgrading to a short-throw shifter for improved feel and reduced travel.

Mounts (Engine & Transmission)

Symptom: Excessive vibration, clunking noises during acceleration or deceleration.

Cause: Worn or broken engine or transmission mounts.

Solution: Regularly inspect the engine and transmission mounts for signs of wear or damage. Replace them as needed. Upgrading to stiffer aftermarket mounts can improve handling and reduce drivetrain movement, but may also increase noise and vibration. After a conversion, it's especially important to ensure the mounts are compatible with the new transmission and properly installed. For example, in a converted BMW E36, using reinforced transmission mounts is often recommended to handle the added stress of a manual transmission.

Troubleshooting Common Issues

Even with careful installation and maintenance, problems can arise after an auto-to-manual conversion. Here are some common issues and their solutions:

Check Engine Light (CEL)

Symptom: Check engine light illuminated on the dashboard.

Cause: Various issues, including incorrect wiring, missing sensors, or incompatibility with the ECU.

Solution: Scan the ECU for diagnostic trouble codes (DTCs). Common codes might relate to the automatic transmission control module or sensors that are no longer present. Depending on the complexity of the conversion, you may need to reprogram the ECU, install a piggyback ECU, or use a simulator to bypass the missing sensor inputs. For example, in older cars like a converted Foxbody Mustang, some mechanics use a manual transmission computer instead of trying to reflash the original automatic computer.

Difficulty Starting

Symptom: Engine cranks but does not start.

Cause: Faulty neutral safety switch wiring, incorrect clutch pedal switch adjustment.

Solution: Ensure the neutral safety switch wiring is correctly connected to prevent the engine from starting unless the clutch pedal is depressed. Adjust the clutch pedal switch to ensure it is properly signaling the ECU. In some cases, the neutral safety switch needs to be bypassed completely if the original wiring is incompatible. For example, some Subaru conversions require careful attention to the wiring of the starter interlock system.

Reverse Lights Not Working

Symptom: Reverse lights do not illuminate when the shifter is in reverse.

Cause: Incorrect reverse light switch wiring.

Solution: Check the wiring to the reverse light switch on the manual transmission. Ensure it is properly connected to the vehicle's wiring harness. You may need to create a custom wiring harness or use an adapter to connect the switch. Confirm the bulb and fuse are in working condition. Finding the correct wiring diagram for both the vehicle and the specific transmission can be crucial in troubleshooting reverse lights.

Vibration Issues

Symptom: Excessive vibration, especially at certain speeds.

Cause: Incorrect driveshaft length, unbalanced driveshaft, worn U-joints, or incorrect flywheel balance.

Solution: Ensure the driveshaft is the correct length for the new transmission and that it is properly balanced. Replace worn U-joints. Verify the flywheel is balanced to match the engine's specifications. In some conversions, a custom driveshaft may be necessary. Checking the runout of the driveshaft is also critical to prevent vibration. A common issue in truck conversions, like a converted Chevy Silverado, is driveshaft length. Proper measurements must be taken to ensure the driveshaft fits correctly.

Real-World Considerations

Beyond the technical aspects, there are practical considerations to keep in mind:

Keeping Your Converted Car in Top Condition

To ensure your converted car runs smoothly and reliably for years to come, follow these best practices:

By understanding the maintenance requirements, troubleshooting common issues, and following best practices, you can ensure that your auto-to-manual conversion is a success, providing years of driving enjoyment.