Speedometer needle bouncing...

[UH60L]

So I got my '69 running for the first time since 2007, and overall it's running great.  I've noticed though, that the speedometer needle intermittently bounces, especially at higher speeds.  Up around 60 it will sometimes bounce all the way to 70 and back as I'm driving. 

Is this just a worn out cable, a worn out gauge, or just normal?  (I don't remember it doing this back in 2007...)

[Lennard]

The grease around the cable might have dried up and is messing with it. I would try to put some lube in there.

[Just 6T9 CHGR]

My jumping speedo would up being the speedo itself....

[XH29N0G]

The speedo works by spinning a magnet with the speedometer cable,  This generates a torque on the speedometer bell.  The rotation of the bell is counteracted by a spring, and the bell is attached to the needle on the speedometer.  When the cable spins faster more torque is exerted and the bell and needle rotate further around. 

Because the torque is small, the movement of the bell and needle is a very delicate balance and any binding that causes the cable to move faster then slower, the magnet to move faster then slower, or something in the assembly of the bell to bind up, can result in a bounce. 

I had this too, and also read the wrong speed.  The fix that you can do is to swap in a new speedo cable to see if it is fixed.  If that does not fix it, then the issue could be something binding in the speedometer itself.  Putting any old oil in is not a good fix because even if it works, it has the potential to collect dust and cause problems later. 

You can try to clean it - I did and failed - or you can send it off to be repaired.  My solution after failing on my original and a replacement, was to buy a replacement (repop one) which was expensive and install that.    Let's hope your issue is the cable.

[71charger_fan]

You should be able to pop the cable housing off of the back of the speedo and pull the cable out of the housing from the speedo end. Then give it a good coating of grease and slip it back in. It cured my bouncing speedo needle.

[Nacho-RT74]

my bid, magnet is dragging the bell quite often

[Brock Lee]

My car did this after I had the transmission rebuilt. They fixed it and said it had something to do with how the speedometer gear was seated into the transmission? I don't quite understand..but whatever they did fixed it..

[Canadian1968]

Mine speedo would bounce at low speeds.  Also involved in the speedo assembly is the odometer. It's linked to the needle/ cable threw 2 worm gears.  This actually was my problem......

[HeavyFuel]

My needle doesn't bounce, but is so far off that I just pace myself based on traffic. 

[UH60L]

Bringing this thread back to life... but hey, I started it.  Anyway, after sitting for 6 more years from 2017 until now, I got my car fixed and back on the road (rear end rebuild).  In the process of getting the rear diff rebuilt, I switched it from 2.76 to 3.23 (mostly because it seems really hard to find new 2.76 gears for some reason...).

It seems to drive great, but the speedometer was way off (like 55mph = 85 on the gauge), and still jumping/bouncing.  So if I did the math right (3.23 gear ratio and 225 60 15 tires) I would need a red 26 spline speedometer gear.  So I bought on off Classic Industries and installed it, and now my speedometer is even farther off (like 55mph = bouncing between 90 and 110 on the gauge).

Plus I can hear noise coming from either the gauge or the cable anytime I'm above about 25 mph.

So, I ordered a new cable from Classic Industries, it's the OER brand one.  Anyone here bought one from them?  What type of grease should I use on it?  Also does it come already greased?

Any info is appreciated.

Thanks,

Clint

[metallicareload99]

My speedo needle would bounce with my old cable that had the jacket burnt in half  I replaced it with what I think was NOS and no more bouncing.

By my calculations I would use the yellow 33 tooth gear

[UH60L]

My speedo needle would bounce with my old cable that had the jacket burnt in half  I replaced it with what I think was NOS and no more bouncing.

By my calculations I would use the yellow 33 tooth gear

Yeah, I had made an excel spreadsheet to auto calculate the speedometer gear size, and I just found the error in it, typed a 5 instead of an 8 when linking one cell to another.  Now it says 33.31.  Guess I'll order another gear.  Hopefully between that and the new cable, I'll be good to go.

[b5blue]

The light lube on a speedo tends to gum up over decades so soaking the needle and all that spins may fix it. (It worked on my 82 KZ440.) I got a new OER brand when my 70 Charger's failed.

[UH60L]

Well crap.  So after I ordered the wrong gear thanks to a math error...  I ordered a 33 tooth gear from classic industries and when it showed up today, it's got a short shaft, like an inch or more shorter than the one in my car.  It's labelled as the correct part and the picture on their website shows the long gear.  Will this short gear work in my 727?

Also, I'v never had to call their support line, how bad is it?

[UH60L]

So, I got a refund from Classic and then ordered the right gear from Mancini.  Also got the new OER speedo cable.  I lubed it with white lithium grease and installed it and put in the 33 tooth gear.  Also verified the right position on the gear retainer plate.

Took it for a test drive.  Good news is no more noise from the cable. Unfortunately at 25mph it showed 30 on the speedometer, then when I went above 45 or so, it started bouncing really bad again.  I goosed it a little and jumped up to 75 or so, then slowed down to 25 coming into the next little town nearby.  After that, no more jumping but 55mph reads at 69 or 70 on the speedometer.

Starting to think my speedometer is bad...

[70 sublime]

The diameter of your rear wheels will make a difference also
I had some really tall 15" wheels on my car and my speedometer was perfect match for speed
Then I swapped on my nice chrome 14" magnum 500 wheels and it reads faster than I am going

[UH60L]

I have the correct gear for my gear ratio and tire and wheel size.  Plus a new cable.  Plus the gear retainer is turned to the correct position for the gear being used (33 tooth).  I'm 99% sure it's a bad speedometer at this point...