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Erratic Speedometer Behavior

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dltowers View Drop Down
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    Posted: Jan/30/2023 at 2:01am
Friends, I have a question about Speedometer Operation....

Recently, when driving my wife's '74 Javelin, I have noticed that the Speedometer "Sometimes" acts Erratic....

**The Speedometer and the Cable Assembly are the factory originals....

I can be cruising along at a steady speed of around 60 mph for several miles, with the Speedometer acting correctly, then all of a sudden the Speedometer Needle will start jumping all around and although I am still traveling around 60 mph, the Needle will start bouncing around to 80-90 mph on the Speedometer Face....

** I can also hear some type of odd noise coming from the Speedometer when the erratic needle behavior starts....

However, after I slow back down to around 40-50 mph, the Needle returns to showing actual speed, and the odd noise goes away....

Like I mention, this only occurs after I have driven the Javelin 25 miles or more at highway speeds....

Could it be a dry or frayed Speedometer Cable or a defective Speedometer?....

Any ideas, thoughts, suggestions, experiences?....


Edited by dltowers - Jan/30/2023 at 2:03am
Original Owner, 1974 Javelin:
360ci,2v,727TC. Motorola Multiplex with 8-Track.
G4 Plum exterior with 421Q Black Uganda Interior. Purchased on July 16, 1974 from Hooker AMC, Sherman, TX for $4500.20
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Jan/30/2023 at 3:12am
This is typical behaviour of a speedometer cable that is needs cleaning and re-greasing.
You can disconnect and pull the cable from the bottom or top ends, pull the inner cable, clean in brake cleaner or mineral spirits and re-grease if not frayed or kinked. Moly grease works well or any other GL-0 or GL-1 grease, GL-2 is too heavy.
Inspect the outer cable especially if you have installed headers as they tend to melt the cables and then you have to replace the whole cable and route away from heat sources. 
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