and at the other it has to be in “P.” Often, the levers that may have been put on your transmission may be the wrong length and you may have “P” or “L” (“1”) but not both.
As difficult as it is to drill holes or modify expensive aftermarket parts, levers may need drilling so “P” and “L” are correctly located and that in “N” and “P,” the starter spins over. Many times it is as simple as changing to the correct lever on the transmission manual valve shaft but it may be hard finding the right one. The total distance the shifter lever moves at the cable attaching point has to match the distance the cable attaching point of the manual lever moves.
Throttle Pressure Linkage
This is by far the most important signal the stock TorqueFlite needs to work properly. The throttle pressure signal tells the valve body where the carburetor or throttle body lever is at any given point in time. Is the engine idling or under load? Is the throttle wide open or did the driver just lift off the gas? The linkage transmits the signal that tells the transmission how hard to shift, when to shift, when to downshift, and when to ease up or increase pressures. If the throttle pressure linkage is wrong, most everything about the shift is wrong. It must be correct.
An intake and carburetor change usually requires a change in the length of the throttle pressure link. As a temporary fix, a 1/4-20 bolt and nut was added to make up the gap.
This longer throttle pressure link corrects the differences caused by a swap.
With the new link on, the rear of the slot is at the throttle linkage pin allowing pressure to be set correctly.
Unfortunately, even though the “top side” of the engine’s linkage can be correct, the lever on the transmission may be wrong. The 2- and 4-barrel engines often had different linkage lengths and shapes, so it may be as easy as switching to a shorter lever or one with the different angle if your linkage is still off. As long as the throttle pressure linkage follows the carburetor or throttle body pin and ends up close to full detent when the carburetor or throttle body is wide open and it goes back when at idle, you can get by without damage. Leaving it off because you do not need “kickdown” is never, ever acceptable unless the lever on the transmission is tied to keep pressure on the internal throttle valve. Even then it is truly only correct at one position unless it is a manual valve body and the pressure is maxed out.
The shift linkage on this 1987 truck uses two plastic bushings to support the horizontal shaft. Always check these for looseness if you experience starting or manual shifting issues.
This bushing is on the transmission side bracket. The lever on the shaft uses another molded bushing into which the linkage snaps. Older TorqueFlites have pins in holes held with clips and cotter pins. The bushings or holes and pins can wear making linkage feel sloppy and cause starting issues.
This truck has a 500-cfm Edelbrock AVS carburetor and an owner-modified throttle pressure link. With the nut and bolt, the rear of the link touched the pin, although it was not the right way to solve the mismatch.
There is another way to take care of mismatched throttle pressure linkage. Bouchillon Performance Engineering and Lokar Performance Products sell cable-operated throttle pressure kits that replace the OEM mechanical rods and linkage. The parts they come with help you adapt to most any combination, and their instructions detail how to set the pressure correctly at idle and wide-open-throttle conditions. If you have changes that render the rod-type linkage too difficult to use, either of these should help.
This bushing is under the driver’s left foot; often overlooked, it is critical to proper gear selection.
At wide-open throttle, the link pushes the throttle valve in the valve body correctly.
“Adapting” to Change
If you have a non-stock carburetor or throttle body, adapters from Edelbrock and Holley help get the linkage adjustments back within stock specifications. The key thing is the throttle valve inside the valve body needs to move in unison with the throttle pin on the carburetor or throttle body. For this to happen, the linkage from the manual shaft on the valve body to the throttle body or carburetor needs to be right and have similar geometry. In other words, the total movement of the carburetor or throttle body pin needs to match the total movement of the lever at the transmission.
Here’s an example. On a 1968 Barracuda with an A-904, the throttle pressure rod’s connection on the transmission to the upper bell crank is adjusted according to factory specs, and it moves roughly 1⅝ inches from baseline (closed) throttle pressure to maximum (wide-open) throttle pressure. Therefore, for the transmission to receive the correct signal, the item that actuates or pushes the bell crank also has to move a total distance of 1⅝ inches. Fortunately, a 4611 Carter AVS (a 1969 340-ci V-8 original carburetor) pin that the throttle cable and throttle pressure link attaches to moves 1⅝ inches from dead closed to wide-open throttle. However, if you toss on a typical Holley carburetor “out of the box” and have to move the pivot pin to the only hole on the Holley that it fits in, which is farther away from the throttle blade’s shaft, the total movement from closed to wide-open throttle is 2¼ inches. If you hook the throttle pressure linkage to it, you find it is out of alignment side-to-side and the length is way off. If you are crafty, you make it fit, but it still may not work. The carburetor can be at idle with the throttle pressure link adjusted so the back of its groove hits the pin on the carburetor lever.
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