Tech Tip: Vacuum Advance

The vacuum advance mechanism for your 1955-57 Thunderbird is located on the outside of your distributor. It is a metal circular disk-shaped housing which is attached to the distributor directly below the distributor cap. On 1955 and 1957 models, there will be one metal vacuum line which attaches to the vacuum advance. On 1956 Thunderbirds there is a dual vacuum advance mechanism and thus there are two vacuum lines attached to the vacuum advance. A vacuum advance that is not working properly will make your car run rough at idle and give you poor overall performance. If you did not check your vacuum advance when you gave your car its last tune up, then this tip is for you.

To test to see if your vacuum advance is working, you can use a vacuum gauge, if you have one, or you can do the following procedure. You will need to remove the vacuum advance from the distributor. First, disconnect the vacuum line leading into the vacuum advance. For 1956 owners, there will be two vacuum lines to disconnect. Next, remove the distributor cap and rotor. There will be two screws which hold the vacuum advance to the distributor. Remove the screws. On 1955 and 1956 Thunderbirds, there will be a metal rod which comes from the vacuum advance and attaches to the underside of the distributor plate. There will either be a small wire cotter pin or "c" clamp holding the end of the vacuum advance metal rod up through a small hole in the distributor plate. On 1957 models, there will be a flat metal rod which is attached to a metal nub on the topside of the distributor plate. I t is also held in place by a small "c" clamp. Remove the pin or clamp and you can pull the entire vacuum advance mechanism away from the distributor.

Once you have removed the vacuum advance, use your mouth and try to suck the air out of the vacuum advance mechanism via the hole where the vacuum line was disconnected. It helps to clean this area of the mechanism before attempting this procedure. If the vacuum advance holds the vacuum, then your mechanism is working properly. You can tell if the vacuum advance is holding the vacuum by placing your finger over the hole before you remove it from your mouth. If the skin of your finger is pulled into the hole opening by the suction of the vacuum, then your vacuum advance is holding a vacuum. On 1956 vacuum advances, make sure you place a finger over one of the holes throughout this procedure.

If you have discovered that your vacuum advance is not working, and your car is a 1955-56 Thunderbird, simply install a new vacuum advance reversing the above procedure for removal. For 1957 owners, however, you must first disassemble part of your old vacuum advance. On the 1957 vacuum advance, there will be a cap at the end of the vacuum advance where the vacuum line is attached. Unscrew this cap. Inside will be an arrangement of washers and a spring. Remove the washers and spring taking note of their order of disassembly. These parts must be installed in your new vacuum advance in the same fashion as they were installed in your old vacuum advance. Once you have "reassembled" your new vacuum advance, you can install it in the same manner as the 1955 and 1956 vacuum advances. Just reverse the removal steps outlined above. Once reassembled, check and adjust your timing, if necessary. Your car should now run much better.

source: CTCC Tech-Tip Manual 1993-1997