The critical connection:
Why proper throttle valve (TV) cable adjustment is critical to a properly functioning transmission.
It's the beginning of Spring for most of the country and that means a lot of you are pulling the cover off the car and getting it ready to hit the road. We want to be sure your're ready to go. There's still a lot of hot rods out there that are running the 700R-4 or 200-4R automatics, and a lot of them have an improperly set TV cable. If you're experiencing poor shift feel, shifts that are too quick or too long, and a general dissatisfaction in the way your transmission performs it could very well be a TV cable that is not adjusted correctly.
Because these transmissions are considerably different from their predecessors (the TH350 & TH400), many guys end up with clutch failures and poor shift response in the 700-R4 and 200-4R. These problems are mainly due to improperly set throttle valve cables. The throttle valve cable resembles the kick down cables of the previous non-overdrive transmissions, but they perform a very different function. The throttle valve cable on the 700-R4 and 200-4R transmissions controls line pressure, shift points, shift feel, part throttle downshifts, and detent (full throttle) downshifts. If the throttle valve cable is not adjusted properly, it can cause numerous transmission problems and/or premature failure.
Above: This is all to often what we find and will ultimately lead to the early death of a transmission. The cable is loose, kinked, and not set correctly. This causes clutch failure due to little or no line pressure off idle and improper line pressure through the throttle range.
Below: With the Tru Shift system installed you get a corrected cable connection with proper cable tension to create line pressure immediately off idle giving the transmission the correct amount of clutch apply pressure to prevent clutch burnout.
The throttle valve cable is connected to the carburetor or throttle body on one end, and the throttle valve plunger assembly is mounted on the valve body at the other end. The throttle valve cable’s function is to transfer the movements of the throttle at the carburetor to the throttle valve plunger in the valve body. This allows throttle valve pressure and line pressure to increase according to throttle opening for gear upshifting. It also controls when the transmission downshifts. When the throttle valve cable is properly adjusted, the movement of the throttle valve plunger in the valve body is calibrated to the movement of the carburetor. This means the transmission will always have the correct line pressure and shift feel regardless of engine torque. The adjustment on the closed throttle side is equally important, as that’s where most failures occur.
The above photo is a great representation of why we do not sell our Tru Shift package without a cable. Often times we get asked if you can use an existing cable and we highly discourage it. As you can see above all of these cables appear to be correct but they are different lengths. With the way the Tru Shift system is engineered we have to be sure that the correct length cable is used, otherwise it will alter the pressure settings we've designed for the kit. We jig test every cable before it leaves to ensure accuracy.
When GM designed the throttle valve cable systems, they were set up for a specific carburetor/throttle body system on a specific intake with the correct bracketry. If a change is made, such as installing a different carburetor, the change in geometry could disrupt this balance and you may never achieve proper adjustment. Often the adjustment gets close enough for proper operation, but it’s never calibrated to what it should be. Therefore, the performance and longevity of the transmission is compromised. All too often, you’ll hear stories of how a newly rebuilt transmission was burned up in only a few miles. This is almost always due to improper throttle valve cable adjustment. It really is that critical!
Many years ago, as we were working on more and more 700-R4 and 200-4R transmissions, we noticed how common it was to see units with burned-up clutches from improper throttle valve cable adjustments. We decided to develop a solution that was so easy to use that there was virtually no way to get it wrong. This led to the creation of the Bowler Tru-Shift system. We spent countless hours developing a correction arm and bracket system that would allow you to install the throttle valve cable onto a variety of popular 4-barrel carburetors, without fear of burning up your transmission. By studying the geometry that GM designed for their system and adapting it onto our brackets, we are able to consistently and repeatedly achieve proper line pressure with a one-time adjustment of the cable during the Bowler Tru-Shift installation. This also allowed us to make a few tweaks to the system to create a little higher pressure off idle. Now, you can better apply the clutch packs when they see the greatest amount of stress getting the vehicle moving from a complete stop. By creating a non-linear cable pull we are also able to apply the pressures at different rates throughout the entire throttle range. This produces a much smoother response in the valve body for gear shifts. There is truly no other throttle valve cable kit on the market today that does what our Bowler Tru-Shift system can.
We are confident that the Bowler Tru-Shift system will produce the results you want and give your transmission the life expectancy and performance you need. The precision of the Bowler Tru-Shift system eliminates any need for checking line pressures, further cable adjustments, and worries of burned up clutch packs. It’s a simple bolt-on solution that comes with all the components you need to get your carburetor connected to your transmission. Regardless of your experience with setting up throttle valve cables, we’re confident that following our instructions will result in a successful installation and a great end result.
Check out the video on the Tru Shift system to see how easy it really is to install and properly set the cable adjustment.
Don't forget about the converter lock up! Bowler Performance also builds a stand alone torque converter lock up kit for the GM 700-R4/200-4R transmissions. Buy both the Tru Shift and Lock Up kit together and get the Total Cure for your transmission installation.
