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Discussion Starter #1
I have a 95 F-350 Powerstroke. The speedometer works up until about 30 mph, then it just goes crazy bouncing all over. I changed the vss and checked the wiring on it. It didn't help. So I decided to change the oil in the rearend. The guy I bought it from said everything worked on it when he parked it. It sat for well over a year though. When I took the diff cover off the tone ring had about a 4 inch strech of bad flaky rust on it. To the point that you couldn't see the teeth on it. I am guessing that there was moisture in the rear end and it settled out while it was sitting. I thought well there is my problem. So I took my die grinder and wire wheeled the rust off and got it clean and shiny. The teeth are badly pitted and miss shapen now from the rust. The speedometer still doesn't work. I think that it is most likely the bad spot in the ring causing the problem. The mechanic I talked to says it can't be the ring or the check engine light would be on and several other problems would be going on. He says it is my speedometer head. I have an appointment to get it scanned and checked on Tuesday. I was just wondering if anyone else had had a bad tone ring or if it was a common problem.
 

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The tone ring is a common problem. They also can get metal shavings built up on them and hinder use. It seems like a bear to replace as pulling the rear gear is necessary I believe.
 

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The tone ring won't set the check engine light. Any tone ring issue will just make the VSS and speedo "think" you're speeding up and slowing down. That isn't a condition that would set a code. Dunno where that idea might have come from.

And the only other problem it might cause would be with shifting an automatic.
 

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Discussion Starter #4
It is confusing the transmission some too. Every once in a while the overdrive off light starts flashing. It has done that twice. My uncle who builds transmissions said that is a limp mode which makes it run full line pressure. It is supposed to get scanned on Tuesday so I hope it shows it is the vss system. After seeing that ring I am about sure it is the problem.
 

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I'm pretty sure it's not a limp mode per se. It's just that the tranny, via the PCM, "thinks" you're speeding up and slowing down. And I wouldn't wait for a scan; if the tone ring is bad, it's bad. Kinda sucks that they couldn't have made a two-piece spit tone ring, which would avoid tearing the diff apart just to replace it.
 

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Discussion Starter #6
No joke. I wish I didn't have to remove the differential to change it. Oh well. I need to get it fixed so I can move on to fun parts like exhaust, guages, and chips.
 

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So is the tone ring supposed to have round or pointed teeth??
 

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Discussion Starter #8
The good ones are rounded then there are a few that are pitted and jagged for about 3 to 4 inches.
 

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talk about 4 yr old thread, id assume tone ring did it for this guy many other variables cause this issue

i suggest you search more old threads or start your own

this is very well covered topic
 

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After replacing the speedo head and wiring from the speed sensor forward and checking grounds in the dash area and pulling the diff cover and checking the tone wheel -----------replaced the non Ford speed sensor with a Ford one and fixed the bouncing needle problem.
 
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