The speedometer has two main
parts, the speedometer head and the speedometer drive cable. When the speedometer fails to indicate speed or mileage, the cable may be broken. Most cables break due to a lack of lubrication or a bend or kink in the housing. The cable also might break when the speedometer head mechanism binds. A jumpy pointer, along with a scraping noise, is often caused by a dry or kinked
speedometer cable. The kinked cable rubs on the housing and winds up slowing down the pointer. The cable then unwinds, and the pointer jumps.
To
lubricate the cable and check for kinks, the cable will have to be removed from the housing. It is not necessary to remove the housing from the vehicle. From under the dash, disconnect the housing by its fluted nut from the back side of the speedometer head. Prior to removing the cable from the housing, cover the carpet and upholstery, as the common lubricant is graphite which will really make a mess to whatever it touches. Using a long nose pliers pull on the cable while supporting the housing. The cable should come out fairly easily unless there is a crimp somewhere in the housing, which could be the cause of the problem by itself.
With the cable fully withdrawn and out of the car, inspect the outer surface of the core for flat and shiny areas. These indicate wear areas and you can use their position to approximate the area of the housing that may have an excessive bend or kink. To check for kinks, lay the cable on a flat surface and twist one end with your fingers. If it turns over smoothly, the cable is not kinked. But, if
part of the cable flops over as it’s twisted, the cable is kinked and should be replaced.
Before reinstalling the cable back into the housing wipe it down with a clean absorbent cloth and re-lubricate it with a graphite bearing lubricant. Then feed and twist the cable back into the housing. The last 3/8” to 1/4” will require twisting and pushing to engage the square drive at the far end of the cable.
Before re-connecting the cable housing to the back of the speedometer head, put a few drops of lubricant on the wick through the hole in the speedometer head. I had a hard time doing this so I removed the speedometer head from the dash. The speedometer can be removed from the back of the head on a 1957 model, so you do not have to remove the entire head.
doug7740
1955 Thunderbird Blue
