Erratic Speedometer

Rick69

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On my 69 Coronet the speedometer needle bounces like crazy when car is moving 0 -20 mph.
20 - 65 mph the needle is steady an accurate. Above 65 mph the needle starts bouncing again. I inspected the drive gear. Looked good. I had an instrumentation shop in Virginia check the speedometer head. They said it tested ok on the bench. The only thing left is the cable. Difficult to believe there is something wrong with the cable when the speedometer works perfectly when cruising 20 - 65 mph. Am I overlooking something?
 

Sam69sat

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You could use a drill and run it counter clockwise (slowly) in the back of the speedometer to see if the needle still bounces below 20mph. If it runs smoothly then it's probably the cable. Could be catching just slightly inside of the cable sheath at low speed causing the needle to jump. Maybe lube the cable?
 

davek

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having the same on my Bee I think it might be the cable. Did you pull out the cable off the speedo and install it again to see if that solved your problem?
 

Ron H

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Had this hassle on my ’63 and seemed to have solved it by removing the cable and cleaning/lubing the tip, not sure if the latter did squat; but did find when I had hooked the speedo cable up before re-doing the cluster, I might not have had the collar fully inserted that might have generated some binding. I futzed with the available slack to ensure a straight shot to the speedo hookup. In my case, the slack is limited and can’t 'see' screwing the collar in – in full view more by feel.
 

Grabbergreendream

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My uncles 67 Coronet does this. Every year we have to unhook the cable from the back of the speedo & pull the inner cable out of the outer sleeve. Wipe it down & grease it up & slide it back in & its normally o.k. for the season. Done it so many times I can do it in half hour or less. He is cheep & wont buy a new cable...
 

Ron H

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My uncles 67 Coronet does this. Every year we have to unhook the cable from the back of the speedo & pull the inner cable out of the outer sleeve. Wipe it down & grease it up & slide it back in & its normally o.k. for the season. Done it so many times I can do it in half hour or less. He is cheep & wont buy a new cable...
Hope he remembers you in his Will.
 

Rick69

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Thanks all for the tips. I will spin the cable with a drill then pull it from the sheathing and lube.
 

Sam69sat

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Thanks all for the tips. I will spin the cable with a drill then pull it from the sheathing and lube.

Just to clarify. When i mentioned spinning with a drill i meant directly on the back of the speedometer without the cable. That way you take the cable out of the equation. If it's still bouncing below 20 then it's probably the speedo. If it's smooth, could be the cable. Either way, it might help to lube the cable and get as straight a shot as possible lining up the cable like Ron H mentions. Be nice if just lube fixes it.
 

Ron H

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What is a speedometer? What are they used for?
Lol, you may be informed when a pole-leese officer pulls you over. I’d suggest not telling da cop your speedo could be off cuz they got just theee ticket for that too. After my re-do of rear gears finding my math was incorrect on the speedo gear I installed, mine reads 7 MPH off. Got too many other friggin projects to do before I work on it...easy-peasy fix-it; but too irritated by my goof to worry about it.
 

1STMP

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My uncles 67 Coronet does this. Every year we have to unhook the cable from the back of the speedo & pull the inner cable out of the outer sleeve. Wipe it down & grease it up & slide it back in & its normally o.k. for the season. Done it so many times I can do it in half hour or less. He is cheep & wont buy a new cable...
Isn't grease in this application a detriment?
Everything I've read, and implemented has been
graphite.
 

Grabbergreendream

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Isn't grease in this application a detriment?
Everything I've read, and implemented has been
graphite.
Always used white lithium grease. Not sure if graphite is a better choice, never tried it. I can guarantee if I used graphite, half the car inside & out would be covered in it by the time is was done!
 

Runner 68

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Lol, you may be informed when a pole-leese officer pulls you over. I’d suggest not telling da cop your speedo could be off cuz they got just theee ticket for that too. After my re-do of rear gears finding my math was incorrect on the speedo gear I installed, mine reads 7 MPH off. Got too many other friggin projects to do before I work on it...easy-peasy fix-it; but too irritated by my goof to worry about it.
I actually got out of a ticket one time by changing the speedo gear. Intentionally threw it off by 15 MPH then had a certified tester test it for $20 and sign the form. (this is of course back when shops were easy to find that still did that) Took it to court and they threw it out and told me to get it fixed. The problem is you can only get away with that once.
 

Slap Stick

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Instead of graphite use a lube with a high molybdenum content such as CV joint grease.
Graphite tends to gum up the works.
At work we used to call the stuff "dirt". When recently applied it works great but over time it tends to gum up the works and needs to be cleaned.
 
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