Answering Your Questions About Speedometers

F.A.Q. – Frequently Asked Questions

These are the questions people ask us most. We hope you'll find answers here that will help.

My speedometer needle bounces; what's wrong?

(A) If there's no noise accompanying the bounce, it's likely that your speedometer cable has been kinked. The only cure for that is a new cable. "Bouncing" can also be caused by the speedometer head drying out. If the oil gets old and dry or collects a lot of dust, it will cause the bouncing.

My speedometer makes a whirring noise; is it ready to wear out?

(A) That "whirring" sound is usually caused by a dry cable. You can detach the cable casing at the transmission end and carefully pull the cable through. Clean it with solvent and dry thoroughly, then grease the length of the cable with lithium-based grease. Feed the cable back through. Don't force it!

The last inch or so, you will have to turn the cable a little so that it will line up with the speedometer. Reconnect everything and test drive. If that didn't cure your problem, then the speedometer head likely needs service.

My speedometer seems slow, how can I check it?

(A) If you have changed to larger tires or changed your transmission or rear-end, it will affect the speedometer reading. You can check the speedometer drive ratio by comparing it to the mile markers on most interstates. A minor error can usually be corrected by changing the driven gear at the transmission end of your speedometer cable.

If your odometer checks out close to correct (within 5 to 8%), then the speedometer magnet has lost its power. You need to take the speedometer to a repair shop where they can usually recharge the magnet and service your speedometer.

My speedometer works but my odometer quit. What happened?

(A) Probably one of the odometer gears is broken. Some of these are short plastic shafts with a worm gear on one end and a helical gear on the other. The fix for that is to take the speedometer apart and replace the gear. Take it to your local speedometer shop; it shouldn't be a big deal. If you don't have a shop near you, send it to us. We will check it out and let you know what needs to be done.

Will you sell me the parts to fix my speedometer?
(A) No, we do not sell repair parts to the general public, although there is good money in repairing speedometers that have been broken by do-it-yourselfers after their attempts of repair. Remember: some of these parts are no longer manufactured and we need them to do our shop work.

I am putting a small bock Chevrolet engine into my 1940 Ford Business Coupe. Can I use the old gauges?

(A) You can use the old speedometer and fuel gauge. The amp gauges do not tell you much with an alternator and most car builders don't like running all of the currents through the dash; they'd rather have a voltmeter. The temperature and oil pressure gauges are nearly impossible to recalibrate to the requirements of a late model engine.