Speedometer Works Intermittently

Trying to resolve this long standing issue with my speedometer. Once I had the drive gear on the D-18 Transfer case installed correctly the speedometer worked. Then one day I noticed while driving that it was reading and then dropped to zero. I observed this a couple of times to try and narrow down the exact symptoms.

Works fine during first part of the drive but then will drop to zero. While reading there is a slight needle bounce. Seems to indicate that somehow the Speedometer is disengaging. Acts like when "Warmed up" something disengages. Since the next time I drive the speedometer works then after a while drops to zero.

Any suggestions on what to check?

The Speedometer Drive gear is in good condition. No worn teeth on the gear and the cable engages with no issues. Same as on the other end with Speedometer Cluster and cable. I Lube the Speedometer as required.

 

I would be looking at the length of the inner cable being a tad short. I had one years back that had the same issues. It seemed the outer cable got stretched by a branch wedging between the frame, making it a bit longer.
-Donny

 

Either the drive gear (inside the transfer case) is bad, or something in the speedometer head.
Do you know what your drive gear looks like ?
Some drive gears had an aluminum hub with nylon gear; the nylon would heat up and disengage when warmed up.
The driven gear is at the cable end.

 

This.

 

Replacement.

If I get the chance this weekend I will pull the inner cable and measure. What length should I expect it to be?

Original, all metal, in good shape the last time I had it apart.

Thanks for all the replies.

 

Long enough to fully engage, but without binding from being over-long.

Some "fits-all" replacement cores have a crimp-on tip... make sure that is tight.

 

There were some brand of cables with too-long inner wire. Cant recall the symptoms. I did have to cut my replacement. Been a long time.

 

In my experience, too long would make the needle jump violently to full scale as the core would bind and release repeatedly. Loosening the nut would relieve that, and I ground off the cable tip until it allowed normal operation with the nut tightened.

That is how I try to fit the Dorman universal cores - better to start with it a little long, than have it too short.

 

If you removed the cable from the housing to lubricate, is it possible that you put it in backwards? I believe they are spiral wound to only turn one way.

 

I believe the drive boss swaged on the top end would normally prevent that. Unless it's loose?

In any case a spiral will twist the same way it was made, in either orientation. Think about a screw thread working from either side...

 

Actually it depends on the manufacturer. Some of the spiral wound drive cables I utilize have an orientation.

 

Yes and there is a reason for this. One reason is to help drive the lubrication from the lower end back into the lower unit. Otherwise you would end up with a puddle of oil in the floor under the speedo head. Another is to coil the core material tight which eliminates speedometer needle bounce. Depending on which way the speedometer rotates will also dictate the core twist.

 

Sure, any spiral wound drive cable needs to twist in a certain rotation.

But still, do they not operate the same in either end-to-end orientation? The rotational forces would not change.

 

Well if you take a left hand spiral and rotate it in a right hand direction it will tend to spring apart and since the core is springy it would grow and collapse
accordingly depending on the resistance between the core and the flexing of the casing.

 

Yes, but that's not my point. Guess I'm not making myself clear.

There was a suggestion to reverse the core end for end, "since they are wound to only turn one way."

It seems to me, the twist direction of the core will be the same no matter which end goes in first. If it is a left-hand spiral, it will be left-hand spiraled from whichever end is used.

If the the spiral would be tightened one way, it would still be tightened if reversed end-for end, since the rotation of the drive will not be changed, nor will the twist.

So flipping it, even if possible, changes nothing.



As for reverse driving, IIRC, jeep speedo cores are two layers, wound opposite to each other. Or am I dreaming that?

 

Yes. When I was doing speedo work I would buy core material by the 200ft roll 1 left and one right. If you were making a core for right spin you cut the core a bit longer and it didn't make any diff which end you swedged the square tip on and then insert core into casing and bend the assy approximately like it will fit into the car. Making sure the swedged tip is seated into the coupling for the speedometer, I would then cut the lower end 1/2" stick-out from the lower coupling. Remove the core and place lower end of core in swedging tool and compress about 1" to make it square. I then burned the end of the core with a carbon arc to keep the core material from fraying and then file the burn to round nub. Lub the core and install in sheath. Note it makes no diff end wise because which ever end your looking at will be the same twist as the other end. That is why you have both left and right twist core material.