fluctuating speedo

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340dustr

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My 70 Duster 340 speedo fluctuates between 0-30mph and smooths out above this.
Have checked speedo drive gear and speedo cable. All seem ok
Could it be a sticky speedo head? Is it possible to lube with light oil?
I have heard of others doing this but wanted to hear your thoughts
 
Don't oil the cable. Pull the core out and use graphite powder to lubricate it. That will fix it.
 
Make sure spedo gear housing is clocked right, corresponding with the the number of teeth on the gear.
 
A jumpy needle is almost always the center cable. Sometimes lubing it helps. It likes to build up a rust pile inside the sheath, right at but not limited to,the low point in the cable. The drive cable sticks in the pile and wraps up, then unloads, driving the needle crazy.Pulling the drive cable out, and working it back and forth thru the rust and breaking it up, will stop this monkey motion.
I take the cable right off the car to do this, and blow it out with compressed air.
However if yours is jumping just to 30mph as you say, it may accept lubing from the top. If it stops jumping, you have postponed the inevitable.

Very rarely is the problem in the head. And if it would be, it's not something most guys can fix.But admittedly, I have had to "adjust" a few.
 
I've cleaned and lubed quite a few speedo cables over years past. Mostly a winter time complaint. Needle jumping and/or making a noise that often lessens as it warms. Keep in mind that those were random brand, lower age/mileage/ daily drivers.
I've ran across a few completely worn out A-body speedometers in the more recent years. What I've learned there is, angular forces on the instruments' input spindle, from the attached cable, is what killed them. So...
Go ahead and attempt to clean and lube cable and sheathe if you want, good luck with that. If not cured and speedometer is repaired/replaced, invest in a new cable as well.
In either case, align cable and sheathe with instrument input as straight as possible.
 
Curious to see if this works...I bought a new cable, but it did not help...also took apart and cleaned bezel..not sure what else to do
 
Steves65 said:
Curious to see if this works...I bought a new cable, but it did not help...also took apart and cleaned bezel..not sure what else to do
Click to expand...

If you have this speedometer out and in hand... Close look at a magnet on the spindle that spins inside a drum. Slim chance that magnetic debris collected inside now dragging the drum thus moving the needle. You'll more likely to find very light scaring from the outer wings of the magnet lightly touching the outside of the drum thus moving the needle.
Here's the point I need to stress... Early repair is replacing some tiny bushings, thrust washers, etc... Not all the parts are interchangeable. If you wait until the instrument breaks that stem assembly with the drum and needle mounted on it, repair will be much more expensive.
 
tjpatte said:
Mine won't go below 30, but reads accurately from there on up.
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Needle never drops to the stop ? Not even if you bump/jar the inst' ? If you wait until it hangs just right and the needle goes all de way awoun, it will break bad.
 
RedFish said:
Needle never drops to the stop ? Not even if you bump/jar the inst' ? If you wait until it hangs just right and the needle goes all de way awoun, it will break bad.
Click to expand...

Nope, had the gauges out and shook it, bumped it, loosened the two screws on the back trying to adjust it, sprayed holy water on it, smacked a virgin over the head with it and nothing:dontknow:

It reads just fine, just doesn't go below 30 like its the stopping point?
 
tjpatte said:
Nope, had the gauges out and shook it, bumped it, loosened the two screws on the back trying to adjust it, sprayed holy water on it, smacked a virgin over the head with it and nothing:dontknow:

It reads just fine, just doesn't go below 30 like its the stopping point?
Click to expand...

I dont know then. Good luck with it
 
Took my gauge cluster out and spun the speedo with a drill-the needle still bounced around like it did when in the car. Guess ill need to see about another speedo
 
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