Weird speedometer issues

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indirect_connection

indirect_connection

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When I first got my car I checked the speedo with a GPS app and found it to be pretty accurate.

Shortly after replacing the engine and rebuilding the trans, the speedometer needle started jumping all around. I pulled the cable out of the back of the speedometer and squirted it with silicone spray lube.

The jumping needle is now an occasional problem, but the rest of the time the speedometer reads steady, but much faster than actual speed. Last weekend I was reading 100mph on the interstate, when I was only going about 70.

I'm looking to replace the cable, but I can't see how a bad cable could make the speedometer read TOO FAST? Did the bouncing needle kill the speedometer?
 
All good thoughts, couple more. DO NOT lube the cable with silicone. Use a light grease. Also, make sure the cable jacket is not (for lack of better word) "stressed" --in other words that the jacket "lays" sort of naturally, and of course that it is routed correctly and anchored. "Frays" on the cable or in the jacket can cause problems which only get worse
 
Cables go bad and exhibit some of the problems you are seeing. Check for cable "wrapping".
 
There is a special speedometer cable lubricant.

What do you use to lubricate a noisy speedometer cable?

It should not get into the speedometer head itself, which takes a different lubricant. I can't remember what I used, but the needle is moved magnetically, it is not mechanically geared to the cable as the odometer is.

Edit: Just checked the factory manual. It says to remove the cable from the housing, and, after lubing the cable, wipe the top foot clean so it doesn't get into the speedometer head, as that can damage it.

Manual doesn't say anything about lubing the speedometer head (that I could find in a quick look), so I'm guessing Ma Mopar didn't anticipate we'd still be running these things 50-60 years later. Been a while since I lubed a speedo head (and they can get very noisy), but I think maybe I used 3-in-one oil. FWIW
 
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Professor Fate said:
^^This- make sure you clocked the speedo drive correctly when you reinstalled it after the rebuild. If not clocked correctly, it could be "jumping teeth".
Click to expand...

Note the numbers on the gear housing - clamp it so that the small number slot that corresponds to your gear teeth is at the top.

Edit: every time I rely on memory I make a mistake. The small number slot should be at the 6 o'clock position, not at the 12 noon position.

s-l1600.jpg
 
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My 67 was doing the exact same thing and also leaking a few drops of trans fluid nightly from the cable housing. I removed and cleaned the housing, changed the seal and O ring and once back together the speedo has been smooth and steady.
 
I remember clocking the housing when I built the trans using the info in the factory service manual. I no longer remember what color/number of teeth are on the gear though. I'll check the cable routing, I might have repositioned it when I installed the cable for the shifter.
I'll also try to clean and lube the cable.
I would just go ahead and buy a replacement cable, but reading through a lot of threads and online reviews saying that the cables listed to fit our cars are incorrect.
 
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