Speedometer finicky.

[Snarky]

Judging from some of the threads I came across in searching I'm leaning towards my issue being a problem with the actual speedometer, I just wanted a second opinion before I drop 30$-50$ on one.

Sometimes my speedometer is fine, sometimes it isn't, lately it's more wrong than right. You'll be cruising about 20-30 miles, often it'll be fine, then you go 40-ish (I suppose) and it does weird stuff, like peg itself past 60 mph. Then it wont work appropriately again till you stop, sometimes that doesn't even correct the problem.

I went ahead and checked the speedometer cable first, it appears to be in good shape, and actually appears to be relatively new, its a barcode on it thats still white, and the sheathing is bright clean plastic, and when you turn one end, it turns the other.


Next I checked the speedometer (gear) adapter, I took it off the transfer case, and aside from being leaky from a bad seal from someone overtightening it, it appears to be moving correctly, I put a similar seal on it to stop the leaking, greased it, and reinstalled it.

I guess by the process of elimination and judging from other threads that leaves the speedometer itself as the culprit. I don't really know how to test it, other than driving the truck and observing whether it works or not, which I do all the time.

Anyone have any other ideas? Anything I missed beyond those parts? Should I go ahead and buy a new speedometer? Could it still be the cable despite outward appearances and the fact the speedometer is receiving rotation?

 

[Barrman]

I agree with your diagnosis. If the cable and gear box are ok, then the actual gauge probably is your problem. I have had bad ones in the past that bounce full scale with the truck in granny 1st and idle, some do fine like yours until a specific speed and then tey take off. One that did this was my 1952 AC speedo in the Gasser. Took me forever to find a replacement that matched the rest of the dash.

Your truck is new enough that any of the metal or plastic cased gauges will work and not mess up the "look."

 

[jollyroger]

Something else you can do to test it is to have a cordless drill attached to the cable on the drivetrain side and spin the cable, slowly at first, to see how and where the speedo acts. You may need a partner for this test in the cab if you don't have enough cable length or arm length to see the dash. I don't want to say this is the case for you because I think you have done everything right so far but sometimes the gear in the drivetrain side gets worn and the cable will skip or freewheel in it. This can cause the speedo to jump all over the place because the cable goes from slack to tight etc.

 

[pittdog]

Change the meter !

 

[saddamsnightmare]

May 11th, 2010.

Mine got squirrelly like that before it quit..... Turned out it was the speedo cable was broken. When I replaced the cable with a NOS one from White Owl Parts, the new cable was smaller od and MFR dated 1967, but with a lubing & installing, they system works OK!
Could just be a gremlin messing with you.....

 

[BKubu]

There was a good article in Military Vehicle Magazine regarding speedometer basics and maintenance. You might also want to consult that article.

 

[Snarky]

Replaced the speedometer today with a new one from boyce, works like a champ now. Went ahead and replaced my rigged up flashers with the correct military signal module while I was at it, also works like a champ.

 

[Heavysteven]

I noticed my gear adpater appears to be lose. Is it supposed to estate at all?