speedometer pointer bouncing

by 76Chevelle2Tone Sat Mar 02, 2024 1:22 am

The speedometer pointer on my Chevelle (rectangular gauge) is suddenly bouncing around. It's particularly noticeable at around 40-50 mph. Sometimes it stabilizes and then resumes bouncing. There is NO noise from the speedometer cable. It was replaced several years ago and well lubricated. Is this due to something with the speedometer cup/magnet assembly, some odd issue with the cable or something else entirely? Thanks for any info.

by zucchi Mon Mar 04, 2024 9:15 am

Does your car have cruise control?

by 76Chevelle2Tone Mon Mar 04, 2024 7:46 pm

zucchi wrote:Does your car have cruise control?

Yes and no. there was a cruise control function and it has the turn lever factory add-on to turn it on and off. However I disconnected it years ago when I replaced the speedometer cable years before I more recently replaced it. So the speedometer cable is much shorter than the original one that was on the car when I bought it almost 35 years ago.

The bouncing started recently several years after the most recent replacement was put in.

by zucchi Mon Mar 04, 2024 8:01 pm

It's always very difficult to nearly impossible to diagnose without SEEING the problem and examining the systems in person.

If you had cruise control, you should have a transducer that looks like this:

There's one speedo cable going FROM the transmission TO the transducer and one going FROM the transducer TO the speedometer. Either of these cables can cause the symptom you're describing. A failing transducer can also cause the symptom. If you bypassed the transducer, it may be your cable; this it the most likely cause. If the speedo cable is close to the exhaust system, the heat will cause it will fail sooner than than it should.
Lastly, your speedometer head may be starting to give out.

by 76Chevelle2Tone Mon Mar 04, 2024 8:20 pm

Given how recently the speedometer cable was installed and the lack of cable noise, I'm fearful that your last option - a failing speedometer head - is likely the cause.

Has anyone repaired or replaced the speedometer head? I assume it's difficult to repair as I have found no parts listed anywhere. Is there a way to lube it or clean it safely? I have found no aftermarket heads for G3 cars either. On the other hand I haven't seen anyone on the site post a thread about it either. Is it highly rare for the head to fail even after this span of years? I assume there are substitutes for the little springs.

by zucchi Mon Mar 04, 2024 8:25 pm

Any speedometer shop worth it's weight in salt can repair and recalibrate it. I've done that for a couple of cars. Just take the speedo out of your car then take it to the shop.

by 76Chevelle2Tone Mon Mar 04, 2024 8:27 pm

OK thanks very much. I'm glad there is an option that doesn't involve me trying to fool with it.

by jaybee Wed Mar 13, 2024 3:29 pm

I would start with the obvious, check cable for ANY possible slight kink / bend that over time could fray the cable inside. Then disconnect at the tranny, if memory serves me you can then pull inner cable out and inspect it, you MAY have to disconnect at the speedo head to pull cable ?. At minimum give it a good cleaning then lube with wd40 or similar. Reinstall then spin with drill from tranny end and have someone watch speedo. Years ago I fixed several old school speedo issues this way. Comes down to a process of elimination. Been there-done that. Good luck.

by 76Chevelle2Tone Wed Mar 13, 2024 3:36 pm

jaybee wrote:I would start with the obvious, check cable for ANY possible slight kink / bend that over time could fray the cable inside. Then disconnect at the tranny, if memory serves me you can then pull inner cable out and inspect it, you MAY have to disconnect at the speedo head to pull cable ?. At minimum give it a good cleaning then lube with wd40 or similar. Reinstall then spin with drill from tranny end and have someone watch speedo. Years ago I fixed several old school speedo issues this way. Comes down to a process of elimination. Been there-done that. Good luck.

Thanks for your reply. Yes I will do that but I was just noting that since the speedo cable was installed only a few years ago and well lubed and not making any noise, it raised the possibility there was another cause. But I have located a speedo head repair shop not that far away so if it is not the cable I am prepared.

by jaybee Wed Mar 13, 2024 10:16 pm

You mentioned lubbing the cable when installed a couple years ago, but failed to state what type of lube you used. I found that a VERY light coating of white grease or a light grease that won't get stiff or harden over time works best. Any resistance for that inner cable will cause speedo bounce. If by chance it's the speedo head, kindly report back with cause and cost of repair. Good luck.

by 76Chevelle2Tone Wed Mar 13, 2024 10:27 pm

Yes it was a light grease. If it turns out to be the speedo head I will report back here what happened as you requested.

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