Jumping speedometer
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Posting Guru
Joined: Jul 2002
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From: Paola, KS
Jumping speedometer
I have a '93 F-150 Lightning that when going over 65-70mph the speedo will jump every once in a while to 10-20mph faster than it is going.
We have replaced the VSS, the instrument cluster, and the EEC.
Anybody have any other ideas?
We have replaced the VSS, the instrument cluster, and the EEC.
Anybody have any other ideas?
New User
Joined: Apr 2004
Posts: 12
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I had the same problem. I took off the rear diff. cover and checked the tone gear in there. One or two teeth were messed up and I noticed that part of the gear wasn't seated all the way againt the ring gear. It was real simple to check out. I had my mechanic replace the gear. I bought it from the ford dealer for $26. The mechanic charged me $100. Works fine now. I've got my cruise control back.
Posting Guru
Joined: Nov 2003
Posts: 1,931
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From: Allen, Tx
The tone ring is purposely missing some teeth. That indicates starting position to the VSS. (it lets the computer know when 1 full revolution of the carrier has happened.)
Last edited by n578md; May 27, 2004 at 03:42 PM.
Post Fiend
Joined: Nov 2001
Posts: 14,947
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From: Topsfield, MA
Um...I've seen two tone rings in my life and neither of them were missing teeth..so I think that might be incorrect.
Check the condition of the rear end itself, not just the tone ring. There could be a bad bearing or side/spyder gear causing the whole assembly to move at those speeds. When the assembly moves, it moves the tone ring which might be what is screwing up the reading, I've seen that happen.
Check the condition of the rear end itself, not just the tone ring. There could be a bad bearing or side/spyder gear causing the whole assembly to move at those speeds. When the assembly moves, it moves the tone ring which might be what is screwing up the reading, I've seen that happen.
New User
Joined: Apr 2004
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The tone ring wasn't missing any teeth. There were a couple damaged. And like I said I think the main problem was part of the tone ring wasn't flush up against the ring gear. Once I tapped it back in place the speedo didn't jump as much. So that showed me that, that was the problem. I had it replaced and it's been fine ever since. I'm just glad I didn't have to replace the psom.
