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Adjusting the throttle valve (TV) cable on your GM overdrive transmission is essential for proper shifting and transmission performance. The TV cable controls hydraulic pressure within the transmission based on throttle position, ensuring timely and accurate shifts. In this article, we’ll go over how to adjust the TV cable on GM 700R4 and GM 200-4R transmissions, explain the differences compared to non-overdrive transmissions like the GM TH350, and discuss compatible carburetors and cable alignment correctors.
What Is A TV Cable And Why Is It Important?
The TV cable, also known as a throttle valve cable, is crucial in overdrive transmissions, as it regulates line pressure based on throttle input. Proper adjustment of the TV cable affects shift timing, quality, and transmission longevity. An improperly adjusted TV cable can lead to delayed shifts, harsh shifting, and even transmission damage, especially in GM TH700R4 and GM 2004R transmissions.
For reference, the GM TH350 transmission uses a kickdown cable rather than a TV cable, which only controls downshifts rather than line pressure, making adjustment less critical than in overdrive models. This distinction is vital when comparing cable adjustments across transmission types.
Components You’ll Need
Before you start, make sure you have the right components and tools on hand:
- TV Cable for GM Overdrive Transmissions: Ensure compatibility with your TH700-R4 or TH2004R transmission.
- Transmission Kickdown/TV Cable Alignment Corrector: Useful for carburetor setups to ensure the correct angle and alignment.
- Edelbrock/AFB Carburetor or Holley Carburetor: The setup will vary slightly depending on the carburetor model.
- Cable Adjustment Tools: Some setups may require wrenches or a screwdriver for fine-tuning.
Note that many new TV cables come with both types of connections for versatility. Use only the connection type that matches your setup.
Adjusting The TV Cable: Step-by-Step Guide
Step 1: Locate The TV Cable
The TV cable connects to the throttle linkage on the carburetor and extends to the transmission. On the GM TH700R4 and GM TH200-4R, the cable is often located on the passenger side of the transmission and is easily identifiable by its connection to the throttle linkage on the driver side of the carburetor.
Step 2: Check The Cable Connection
Most new TV cables include both types of connections to fit different setups, but you only need to use one connection type. Attach the cable to either the Edelbrock/AFB carburetor or Holley carburetor throttle linkage, depending on your setup.
Using a Transmission Kickdown/TV Cable Alignment Corrector is essential for aligning the TV cable at the correct angle with your carburetor. Incorrect alignment can result in inaccurate shift points, so it’s a crucial step for proper adjustment.
Step 3: Set the Cable Adjustment at Wide Open Throttle (WOT)
- Ensure the Engine is Off: For safety, make sure the engine is turned off during the adjustment process.
- Press the Adjusting Tab: Locate the adjusting tab on the TV cable housing, which is a "solid D" shape. Press the tab to unlock the cable and allow movement.
- Open the Throttle to Wide Open Throttle (WOT): Manually open the throttle to its maximum position (WOT).
- Pull the Cable Housing: While the throttle is still at WOT, pull the cable housing backward until it is fully extended and then release the adjusting tab to lock it in place.
- Release the Throttle: After locking the cable, release the throttle back to its idle position.
Setting the cable at WOT ensures the proper tension across the throttle range, allowing for accurate pressure adjustments within the transmission and optimal shifting behavior.
Fine-Tuning Your Cable Adjustment
After setting the baseline adjustment, take the vehicle for a test drive to observe shift quality and timing. Here’s what to look for:
- Early Shifts: If the transmission shifts too early, try loosening the TV cable slightly.
- Delayed Shifts: If shifts are delayed, increase the cable tension by pulling the cable housing backward slightly.
Adjustments should be minor, as over-adjusting the cable can result in transmission damage.
Cold Weather and Cable Performance
Cold temperatures can cause the TV cable to contract slightly, affecting shift timing. If you experience noticeable differences in shifting during colder months, make slight adjustments to the cable to compensate for the temperature. Always make sure the cable operates smoothly, as stiffness can impact throttle response and shifting.
Using the TV Cable with Different Carburetors
Edelbrock/AFB Carburetors
If you’re using an Edelbrock or AFB carburetor, you may need an adapter for the TV cable to attach correctly. Proper alignment is essential with these carburetors, so use a TV Cable Alignment Corrector to maintain the right angle and geometry.
Holley Carburetors
Holley carburetors typically have a dedicated TV cable mounting point, making it easier to install without additional adapters. However, you should still use an alignment corrector to ensure accuracy, especially if your setup differs from the standard.
Comparing GM TH700R4 and GM TH350 Cable Adjustments
The GM TH350 transmission uses a simpler kickdown cable rather than a TV cable. This cable only controls downshifts, with the throttle typically at 90% or more activating the kickdown function and is less sensitive to adjustment. In contrast, the 700R4 and 200-4R transmissions rely on the TV cable for all shift points, meaning adjustments are far more critical. An improperly adjusted TV cable on a TH700R4 or 200-4R can result in immediate transmission damage, while on the TH350, it simply affects the kickdown function.
Final Tips for Adjusting Your TV Cable
- Double-Check Alignment: Proper alignment with the carburetor ensures accurate shift points.
- Use the Right Connection: Many cables offer multiple connection types. Choose the one that fits your carburetor to prevent issues.
- Perform Test Drives: Small adjustments based on road testing can help fine-tune shift quality.
- Consider Professional Help: If you’re unsure about adjusting your TV cable, consult a transmission specialist such as a JEGS Tech Support representative to avoid costly mistakes.
Properly adjusting the throttle valve (TV) cable on your GM overdrive transmission, whether it’s a TH-700-R4 or 200-4R, is essential for smooth and reliable shifting. By following these steps and using the correct components, such as alignment correctors for Edelbrock and Holley carburetors, you can ensure your transmission performs optimally. Remember to take small steps, perform test drives, and adjust carefully to protect your transmission and maximize performance.
