This is really weird. I know the speedometer is run by a cable with a gear into the tranny and attaches at the speedometer.

Recently, when the truck is cold, the speedometer doesn't work at all. Then, about the time the engine is warming up, the speedometer jumps from not working at all to like 80 mph for a split second and then settles at the current speed, usually 45-55 mph.

The only thing I can think is that the cable is binding somehow, and then after a certain amount of rotational leverage is applied, it breaks loose, winds up excessively (the 80 mph), and then settles back to normal indication.

Question is, has anybody seen this before? Is my best bet to apply some graphite lubricant to the cable, or just replace the speedometer cable ($20)?

My thinking is, if I have to open up the dash anyhow to put the lubricant in, I might as well go ahead and change the cable.

Could it possibly be an issue with the speedometer itself or the gear in the transmission? I've seen the gears get stripped before and when that happens the speedometer jumps around, ie, a different indication than what I'm seeing.

TIA,
Sam

 

It's most likely the speedometer head itself. It's needle is freezing in the head. When it warms up the parts expand a small amount and the needle turns free again.

The heads are a magnetic and gear drive type.

The gears operate the odometer, the magnets operate the speedometer needle.


Check the odometer, is it turning normal before the needle starts to work?


Not much you can do about it that is "proper" except replace it.

However.... You can spray a small amount of lubricant on the shaft and the holes it goes through, that drives the speedometer needle. I have fixed some using white lithium grease and/or WD40 to draw the moisture out of the head so it doesnt freeze. And I mean use it very spareingly.

When you have everything apart check the cable as well. If it's frayed or damaged buy a new one, If it looks great, clean and repack the cable with white lithium grease or a special speedometer cable lubricant.

Hope this helps..

 

I can't add anything technical it is all already there

 

Thanks guys. I'll post back with how it goes.

 

Ford makes this:

D2AZ-19581-A Speedometer Cable Lubricant

While jumpy speedos usually tied to the heads, a dry cable will cause it too, because without grease, the inner speedo cable core will bind against the outer speedo cable housing.

Speedo cables are two pieces..inner/outer.

 

OK fellas, I have been able to deduce that the odometer does work all the time, and is still working even when the needle is not moving.

I took the dash apart and looked at the speedometer, and man there's not that many moving parts to the magnetic assembly. I'm not sure what could be wrong with it or why it would work sometimes and not others, or how any moisture on it would affect it when its cold.

Anyhow, looks like I need to get the speedometer repaired or replaced.

Here is a used one on ebay...
http://cgi.ebay.com/ebaymotors/ws/eB...m=330088921463

Is this problem with the magnets common? Is it likely I will have the same problem with a replacement used speedometer? For $25 I don't think I can beat trying the used one, but this truck is my daily driver so I need it to be reliable.

Is there any speedometer repair places any of you consider to be reputable that would be able to repair my original speedo?

Thanks,
Sam

 

I myself would just squirt a little bit of WD-40 on the shaft. You will notice a little spring as well. Make sure that every place where the shaft goes through metal like the little bushing behind the spring, gets a tiny squirt. Not much, just a little. like a few drops.

Nine times out of ten this will fix the problem.

As for the moisture, the metal will "fog up" just like the windshield does on a cold morning. The WD-40 keeps the moisture out of the bushings and shaft area, and also helps lubricates "a dried out one".

hope this helps.

 

Check your yellow pages for speedometer shops. There is usually at least one in major metro areas. A large truck repair facility may also know where one is that they use.