Strange speedometer increase without RPM increase

Seemingly random while driving 40 ~ 50 mph the speedometer will occasionally jump up about 5mph and settle back down without the RPMs increasing along with what the speedometer is reading. Not tachometer, the speedometer. No stepping on the gas to go faster or taking foot off the gas to slow down, just while holding it steady cruising along.

If it was tachometer I'd think maybe the ECU (as I had that issue on the '93 mitsu I have) but I have no clue what could be causing this. Is this an automatic transmission related issue? Or is there a sensor or cable or something I should check? Really lost! Admit it's only been about 2 hours total of driving time so far since I got it so not sure if it always does this or not.

I can't find anything about this in the book & forum searches only gave me more things to do on other lists, lol.

Anyone have this happen before? What was it? Or could it be?

Wasn't sure what topic to put this in, hope it's okay here, thank you.

Diagnosis: Mitsubishi.

The truck, like Herbie the Love Bug but more costly, is telling you how fast it wants to go, but can't at the moment, because something will break.

Check the fittings at both ends for snugness? Maybe the worm gear is getting worn or is slipping.

Speedo cable is most likely worn out or the actual gearing in the cluster for the speedo is worn.

Mine does the same thing... it's not a big deal that it does it unless you really have no clue how fast you're going.

i would try the easy/cheap attempt: disconnect the cable from back of the instrument cluster (all work can be done from the driver's seat) & spray a decent volume of graphite lube (ie: http://www.amazon.com/Blaster-8-GS-G...2M9WMK58K5YN3A ) down the inside of the spedo cable....not to be confused with this spedo http://ts4.mm.bing.net/th?id=HN.6080...992263&pid=1.7

I second lubing the speedo cable - if they bind it will start to cause fluctuations - if left go long enough, the cable will break.

& if it breaks...it may take a little effort to find "This product is no longer available": http://www.factorychryslerparts.com/.../MB113869.html

Is that picture up there hurting anyone else's eyes besides mine? :lmao: or maybe I just spilled chlorine in them.:eek1:

Reminds me of Ben Stiller in the movie Dodge Ball.
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Originally Posted by ragragtimetime

not to be confused with this spedo
http://ts4.mm.bing.net/th?id=HN.6080...992263&pid=1.7

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I believe this is technically a singlet, not a speedo.

Luckily I can't see the pic, just a box with a camera and a circle/line over it :P

But I will go ahead and spread around some graphite & see how that helps. Wouldn't you know it, this morning I didn't catch it moving itself up! The e-brake was kind of sticky, too, for the first day of driving/parking, so may as well use graphite, oil, or lube everything I can find. Already did the bottom of the truck, time for inside I see. Thank you for the ideas!!! Yeah, a broken one would be terrible!!!

and Noah: "Diagnosis: Mitsubishi." roflmao I'm going to have to remember that one! Darn truck, lol.

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Originally Posted by tink

Noah: "Diagnosis: Mitsubishi." roflmao I'm going to have to remember that one! Darn truck, lol.

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They're shitboxes, but they're our shitboxes.