Tech Tip - Automatic Trans Shift Adjustment

Automatic Transmission Shift Adjustment

The 1955-57 Thunderbirds, with Automatic Transmission, use a mechanical transmission shifting mechanism. The speed at which your transmission shifts from one gear to another is determined by the length of your kickdown rod. You can vary the shift of your transmission by increasing or decreasing the length of this rod. In cars of more recent vintage, including your "daily driver", your transmission is shifted using vacuum power or electronically via your onboard computer. The speed at which your Thunderbird's transmission should first shift should be at approximately 28 miles per hour. If your Thunderbird has its correct engine and transmission the following information will allow you to adjust the shift of your transmission. Once again, I thank Mr. Ken Smizinski for providing me with this month's "tech tip."

To adjust the shift of your automatic transmission you must first locate your kickdown rod. This is labeled part number 7A187 in the accompanying diagrams. It is located on the driver's side of the engine and rises up from the base of the firewall and attaches to your bell crank, part number 7A185, which is attached to the rear of your intake manifold. You should notice that at the point where your kickdown rod is attached to your bell crank there is a threaded adjusting rod which when screwed onto the kickdown rod allows for the necessary length adjustment. This part is labeled 97011-S and 7354 in the accompanying diagrams. You can remove your kickdown rod from the bell crank by removing the cotter pin from the adjusting rod. The kickdown rod should slide right off of the bell crank once the cotter pin has been removed.

With the kickdown rod removed from the bell crank you should be able to see a set of "pilot holes" on each side of the bell crank. By pivoting the two parts of the bell crank you should be able to align these "pilot holes" so that you can place a 1/4" dowel or 1/4" drill bit through the pilot holes on both sides of the bell crank. With this done, you have found your preset alignment point for your transmission as well as your throttle rod and accelerator peddle clearance. For right now, however, we are only concerned with your transmission. Next month, with help from Ken Smizinski, I will attempt to explain how to adjust your throttle rod and accelerator peddle.

The point at which you can place a 1/4" dowel or 1/4" drill bit through the pilot holes in your bell crank is the point at which the engineers of your Thunderbird provided you with a preset alignment position. From this point your kickdown rod should be two and one-half turns counter-clockwise, "longer," than a perfect slide-on fit back onto your bell crank. To better explain this, if you pull up on your kickdown rod and try to attach it to your bell crank housing, you should adjust the length of the kickdown rod so that you have to push it down only so slightly. This can be measured by lengthening the rod enough so that it just slides back onto the bell crank when the kickdown rod is pulled up. Once you have found this point, lengthen the rod by turning the adjusting rod two and one-half turns counter-clockwise so that the kickdown rod is just slightly too long. You will be able to slide it onto the bell crank, but you will have to push the kickdown rod down ever so slightly. At this point you will have adjusted your Thunderbird's transmission to shift according to factory specifications. Your Thunderbird should shift at 28 miles per hour.

Don't forget to replace your cotter pin!!

Source: CTCC Tech-Tip Manual 1993-1997