Jumping speedometer

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Jan 26, 2012 | 12:07 PM

strokin'_tatsch

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From: Austin, TX

Jumping speedometer

Hey guys. I've got a problem with the speedometer in my F-150 that I'm trying to figure out. It works nice and smooth just like it's supposed to from 0-~65mph. When I start approaching 70mph, the speedometer goes crazy and will jump about 20mph in each direction, so down to 50 and up to the peg. If I slow down back to 60-65mph it will stop and stay smooth until I speed up again.

So, lets hear y'alls thoughts. I have rebuilt the 8.8. It has new everything, including tone ring and VSS. The VSS is a part store piece and the tone ring is new from Ford...

So, does anyone think that the tone ring could be the problem? I can't help but wonder if the tone ring is slightly crooked or something, causing the VSS to not "see" the tone ring. I would think if the tone ring was the problem though, it would do it at all speeds. Anyways, lets hear what y'all think. Any help is appreciated. I don't even know where to start. LOL

Jan 26, 2012 | 02:41 PM

gasman6674

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From: Greenwood In. USA

How is the harness on your vss. I changed the vss in my motor home and it was a bad harness.
Hope this helps

Jan 26, 2012 | 02:51 PM

strokin'_tatsch

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From: Austin, TX

I still need to run through the harness. Anyone know a good way to test the harness rather than tearing it all apart and looking for bad wires? The wires look good for the first 6-7" I know b/c I have looked at that portion, but haven't gone farther up.

Jan 26, 2012 | 02:53 PM

RIKIL

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If this is for your 94 or 95 and you have an electric speedometer, you might have troubles with speedo itself. I tried to find an old post of mine but I couldn't. In that post I describe how the components that are soldered on to the back of the speedo weren't cleaned properly when they were originally soldered on and they were coming off. This made my speedo do the same thing as yours, only difference is that it didn't matter what speed I was going.

I had a friend of mine solder everything back on and it worked great. You might be having a similar issue.

HTH

Jan 26, 2012 | 03:13 PM

gasman6674

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From: Greenwood In. USA

Actually no
The connector had been replaced on mine and I just ripped their splices apart and put on a new pigtail.

Jan 26, 2012 | 03:30 PM

strokin'_tatsch

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From: Austin, TX

Well, I have another instrument cluster here and I'm replacing the instrument bezel in the next week or two anyways, so I will pull the instrument cluster and check it out. See if anything looks out of place. If nothing else, I could throw in my spare cluster and see if it works better.

Jan 27, 2012 | 09:13 AM

robertsblk70

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I had the same issue at 70 mph and ended up taking the PSOM to a Speedometer shop. They had a TSB from Ford that provided them with the required fix which was replace the PSOM board with a new unit which they told me buffered out the spikes from the VSS. I don't know if all thius is true but it fixed my jumping speedo.