The kickdown linkage in my 1968 Mustang coupe worked fine when I test drove the car, but not for long after. Minutes after money changed hands, the first time I put my foot to the floor on the road north out of Carolina, the kickdown linkage popped.
I drove the car that way for a few months. Unlike later overdrive transmissions that burn up when their throttle valve cables are disconnected or out of adjustment, missing or maladjusted kickdown linkage won’t damage an old three speed Ford C4 automatic. The C4’s vacuum modulator will shift the transmission ok during normal driving. Without a properly installed and adjusted kickdown however, the transmission will not drop from third to second gear under hard acceleration, and during normal driving the two-three upshift comes very quickly. You can still manually downshift for a passing gear, or for a spirited run down a country lane, but engine vacuum alone doesn’t give the transmission enough information to operate at its best.
Rather than a bulky factory rod or pricey aftermarket cable running from the kickdown lever up to the carburetor like many old cars, the Mustang’s C4 kickdown lever is connected to an accelerator arm under the driver’s side toe board via a short cable. Complete factory style replacement kickdown kits are available for less than forty bucks. We installed a Scott Drake kickdown kit, which comes with everything you need, except instructions. No kidding. So, here’s how to install and adjust the kickdown cable linkage on your classic Mustang.