GM Full-Size Trucks 1970-1979 Repair Guide
Speedometer Cable Core
Disconnect the battery ground cable.
Disconnect the speedometer cable from the speedometer head by reaching up under the instrument panel, depressing the spring clip and pulling the cable from the head.
Remove the old core by pulling it out at the end of the speedometer cable casing. If the old cable core is broken it will be necessary to remove the lower piece from the transmission end of the casing. It is also important to replace both the casing and the core.
Lubricate the entire length of cable core with speedometer cable lubricant.
Install the new cable by reversing steps 1 through 3 above. Use care not to kink the cable core during installation.