Speedometer cables can be annoying, especially when you notice the crazy gyrations coming from the speedometer needle that jumps, skips or does not move at all. The problem looks serious and might lead someone to think that the engine can be at fault. In reality, the problem almost always lies with a twisted or kinked speedometer cable, or a cable that has lost its lubrication through wear and age.
Examine the new cable against the old one that was removed. Pay particular attention to length and width. They will have to be an exact match, and you will have to stretch the old cable out to relieve the stress to get the proper length. Compare the end fittings. They must match up, and there will be either rectangular fittings, slots or some other insert design that fits into the speedometer box side and the gear box or transmission housing. Make sure you know which end goes with which fitting.
Lay the new speedometer cable on a clean surface like a large piece of cardboard or a plastic tarp. Make sure any surface you use is clean, having no dust, sand or debris on it. Even the smallest grains of sand that enter the speedometer cable housing can eventually destroy the cable by grooving or fraying it. Apply a liberal amount of grease on the cable from one end to the other. Use back-and-forth strokes evenly over the entire cable surface, stopping about 3 in. from each end. Turn the cable over and make sure the underside has been coated--you want a medium to thick coat all around, with no globs or bunches. Too much grease will be forced out of the cable housing during installation and make a mess.
Align the cable housing as straight as you can on the tarp's surface. Reform any twists or bends in it by applying pressure. If the housing is new, it will present little problems. Inserting a new cable in an old housing takes dexterity and patience. Run the cable in through one end, twisting it around in a circle as you go--this will spread the grease on the inside of the cable housing. Stop if you meet resistance. Pull it out if necessary. Start feeding it again, twisting as you go. If it binds at any time, remove it and straighten the cable housing and try again. Once you have it completely installed, wipe excess grease from both ends.
Feed the cable through the appropriate routing holes from the dashboard side (in back of the speedometer gauge) through the firewall and down into the gear box or transmission housing. Secure it with the retaining straps. Twist the cable end cap on both connections with channel locks. In the case of a bolt-mounted gear box or transmission cable connection, tighten the mount to secure the cable end.
Test the speedometer cable by driving the vehicle.
Use the correct tools if you need to remove an old cable from a housing for the purpose of lubricating it. Disconnect the end cap from the speedometer gauge and the (screw-on) end cap from the gear box or transmission housing.
Never bend or force the cable housing back into position. Slide it gently.