Erratic speedometer

[Crossram413]

Hi folks,
I recently reinstalled the gauge cluster in a 72 Challenger 340 auto with rally gauges. I didn't know if the speedo worked before since the needle had been broken off but is now replaced. Took the car out last night and the needle jumps wildly. A search of the forums finds no thread on this, googleing points to cleaning and lubing the cable.
What are your expert opinions? if it is clean and or lube, and helpful tips?
Thanks!!

 

[fasjac]

If it’s the original cable, I’d go ahead and replace it. Make sure it’s snapped in good on the speedo. Check the condition of the plastic gear as well. They get brittle over the years and loose teeth. If you done this already, go back to speedo itself. JMO

 

[Steve340]

Start with checking and lubrication of the cable. That may fix the problem - or not but do it first then move on to the hard stuff.

 

[Tom's EK2]

My experience-
Speedometer needle started jumping ,awful noise, cable broke.
If you have the original cable there you should probably just replace it.
Also, most likely why you had to replace the needle in the first place.

 

[moparleo]

Resolving Speedometer Problems on Classic Cars

 

[Crossram413]

Thank you all, this forum is great!
I pulled the inner cable, it looks perfect. I lubed with liquid graphite cable lube.
The bouncing of the needle is not as extreme, but as I eased back into the garage the speedo was waivering between 60 and 80.
Thoughts?
Doug

 

[Chryco Psycho]

clean & lube the actual gauge .

 

[Adam]

And speedo cables are dirt cheap... less than $20.

 

[Jimmmmmay]

I don't know if it'll help, but I dealt with this recently and found it was the speedometer itself. The cable that was in the car wasn't correct, so I got a new one of those and lubed it - still bounced. Then I checked the speedo gear in the tranny and it was fine (although messy to check - I have a 4spd and tried to jack the car up high in the back to minimize the fluid that comes out).

Finally I gave up and just got a new speedometer from OER. That was the issue for me. I found after I got the old speedometer out, it was sloppy. If I held it upside down, the needle went to the 20mph mark and flopped around a lot, while the new one didn't do that. I did try hooking up a drill to the cable to see if I could reproduce the problem without driving the car. The only thing weird that I noticed was that if I pushed the cable inwards kind of hard while spinning it the bouncing seemed to not be as bad. So, basically I fixed it by replacing everything , but in the end it was was the speedometer for me. Side note, the OER speedometer doesn't come with the red tape that covers the hole for the high beams indicator.

 

[Crossram413]

Thanks for the thoughts. I'm going to lube once more, if that doesn't work I'll replace the cable. Last resort will be to send the speedo head out for repair

 

[Litchkar]

look at the speedo gear housing on the tail shaft. If it is not indexed correctly, needle will bounce and wear the teathdown. It is stamped with the number of teeth range to index it to the correct gear

 

[NoCar340]

One thing I haven't seen mentioned is the cable's routing. Make sure it's routed correctly, with no sharp turns or bends in the cable housing. Any change of direction needs to be a large, smooth radius to keep the inner cable from binding inside the housing. If it binds, the inner cable acts like a torsion bar and builds tension along its length until it frees itself: No reading, then suddenly 100MPH, then back down to zero as it binds again.

If you're shopping for a new cable, be aware that ATP and Pioneer list cables that are too long. Check the length of the new one against your original before you buy.

 

[fasjac]

Just thought I’d put this out from FSM, you probably have the correct gear. Just for reference

 

[Crossram413]

Relubing the cable seems to slightly improve the situation. perhaps this will improve over time as the cable loosens up. Any preference on lube? I'm using a liquid graphite.

 

[Steve340]

I use a very light synthetic grease. Lube by sliding the inner cable through your fingers and spread the lube evenly - and do not over lube.
Do not use a mineral or chassis grease they are too gooey and thick. They also are wax based and the oily part of the grease goes and leaves a waxy residue that caused problems with the cable.

 

[flohemi]

Back in the day, maybe late eighties, we had a problem with bouncy Speedo,s we used to pull the inner cable out, clean and lubed but one thing we had to do is trim the end of the cable where it went into the Speedo about a sixteenth of an inch, cut the point off if it has one. Good luck

 

[ctaarman]

Hi folks. May I join in with a slightly different speedo issue. previous owner of my AAR Cuda had the needle break off, but the remainder of the needle worked smoothly. As part of a restoration of the entire dash, I pulled the speedo, gently took off the old needle per instructions (holding that back firmly as to not rotate). Installed the new needle similarly. Snapped the speedo cable back in. Now the speedo doesn't work at all, but I know the cable is engaging because the odometer is working correctly. Any thoughts please?

 

[Rons340]

I have run across a few cables where the inner cable was slightly longer than it should be. This will cause the inner cable (chain) to bind and produce erratic operation.
I would suggest installing it, but leave it unlatched from the head temporarily. Drive it like that, or run it on the lift, if it fixes the issue then this is likely the cause. Now, which end? Reconnect it back to the speedo head and disconnect it from the speedo adapter on the transmission. Move it in and out to see if you have any slack. There should be around 1/8" or so. If you have that relief then the top is good. If that is not the case, simply clip 1/8" or so off the plastic tip and recheck for the proper relief. The top of the cable seats in the housing so latching it in place could bind it even if the cable is routed correctly and properly lubed.
If you are good at the top then carefully install it back into the speedo adapter and be sure the inner cable does not bottom out in the gear before the cable housing seats against the adapter. If it bottoms out you will need to clip off enough of the chain to allow the housing to comfortably seat and tighten against the adapter.
It sounds like a lot but it really isn't. You will properly eliminate the cable by doing this and possibly avoid buying a speedometer you didn't need.

Rons340