What makes a speedometer bounce

More sharing options… In some cases it can be a build-up of dust, grime or dried out grease on the moving parts inside the speedometer.

This is just an example and not your actual speedometer head. Yours will be similar. No sensor on the trans for the speedo, only the VSS. Carefully check the wiring between the VSS and the front of the truck for worn wires, specifically the twisted pair of wires going to the VSS that run all the way to the front of the truck.

Also check the grounds as mentioned. This noise should be similar to a scraping and ringing noise when it momentarily happens with each revolution of the speedometer cable.

What needs cleaning and lubing is the small bushing in the end of the main shaft that holds the end if the speed cup.

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What are the advantage and disadvantages of the bandala system? There is a spring on the back inside that puts tension on the the spinning magnet to keep the speed steady.

But don't just put more tension on it as it will then show a speed too slow. That tension is what calibrates the speedometer. What ALSO might be an issue is internal wear of the cable housing's inner surface.

By this time, most cables were of a plastic nature with some metal wire reinforcement. Typically, the bushing in the back of the speedometer head is also plastic. It can deteriorate with time and mileage, too. Lubing it will only add more lube where it normally isn't needed or desired. Replacement bushings when the head is rebuilt by a speedometer shop are usually oil-impregnated bronze similar to door hinge pin bushings , which lasts much longer.

As you mention "noise", my suspicion is that the rear plastic bushing has worn, which lets the spinning magnet side rear of the speed cup rub the other side front of the speed cup attached to the actual speedometer needle's shaft.

This noise should be similar to a scraping and ringing noise when it momentarily happens with each revolution of the speedometer cable. Each "touch" can make the speedometer needle jump. The actual speed calibration is done with "magnetic intensity", meaning a stronger magnet makes the front speed cup want to follow it more closely and weaker magnetic forces do the opposite. At the speedometer shop, to effect such calibrations, it's a cut and try method with a "zap gun" for those who were around in the earlier days of color television, you might remember the "degause" treatment of the picture tubes.

The "clock spring" on the front speed cup ensures that the speed cup's resting position is at the "zero index" point on the speedometer's face plate. It could well be a special clock spring which makes this close-calibration possible, as well as tighter quality control. In conclusion, I suspect your issue could be a combination of issues. One of possible inner cable housing wear plus normal wear of the speedometer head's rear bushing.

IF the car has cruise control, the governor weights in the cruise control "head" might also be an issue, too. Without knowing how many miles are on the car rather than get into a bunch of speculation I'd simply replace both portions of the cable. They're cheap and don't really take that much time to replace. Worse thing that will happen is the noise doesn't go away. I've cars that are over 50 years old and to my knowledge have never had an service done to the speedometer or cables and have yet to suffer what you are experiencing.

Or sell the car and buy one without a bouncing speedometer needle. I can't sell it, I got it the week after I got my driver's license. That building was my dad's GM dealership. Our building had been there since the '20s. Anyway, I suppose I'll just try to take the cluster out and using the suggestions here see if I can look at the mechanisms and see what's wrong.

Speedometers are still a bit of black magic to me, so I have a fear of breaking them and not being able to put them back together again.