I have a VDO speedometer that was recently refurbished by Palo Alto Speedometers, who also supplied a matching cable. The needle is steady and moves smoothly when the cable is attached to a variable-speed electric drill. But when installed in the car the needle bounces around. It seems to be effected by road bumps, but even on relatively smooth surfaces it still wanders.

If the speedometer and cable are fine in a bench test, I’m assuming it has to do with how the cable is attached to the wheel. Or maybe not. Any ideas?

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Are you using OEM front left spindle or aftermarket dropped/disc spindle?  Wonder if the bore where the speedo cable goes thru the spindle center is dirty, rusted or not polished smoothly?   This would cause the cable to bind.  I'd get a gun cleaning brush (22 cal?) and run it through to clean it and then grease the bore.  Also do you have a secure clip on the square end of cable as it exits the wheel bearing cap and is the bearing cap bent or not mounted straight? A tight bend in cable under dash/gas tank might also cause it.

It could also mean that your speedo cable is a tad too short, causing a tight radius turn somewhere in its path which makes the cable "flip" inside of the cable cover as it rotates.  That flipping causes the needle to wobble slowly at low speeds, and the wobble speeds up to a vibration as the car speeds up.  The answer to that is a longer cable allowing more gentle turns on the way to the speedo gauge.

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