Speedometer suddenly wacky
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Freshman User
Joined: Mar 2002
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From: Spokane
Speedometer suddenly wacky
Drove to work the other day and everything was fine. Then went to do some errands and jumped on the freeway.
For no apparent reason the speedo dial "floated" up to 75-80 mpg even though I was going with the flow in the right hand lane (60ish).
Does this off and on now whenever I am at highway speeds. Around town it seems normal and sometimes on the freeway it seems normal. But I can never be sure now how fast I am going.
Is it possible for this to be an intermittent problem.
Any ideas what is the cause?
Thanks, Gobstopper
1977 F-250 supercab 400, auto
For no apparent reason the speedo dial "floated" up to 75-80 mpg even though I was going with the flow in the right hand lane (60ish).
Does this off and on now whenever I am at highway speeds. Around town it seems normal and sometimes on the freeway it seems normal. But I can never be sure now how fast I am going.
Is it possible for this to be an intermittent problem.
Any ideas what is the cause?
Thanks, Gobstopper
1977 F-250 supercab 400, auto
Posting Legend
Joined: Sep 2001
Posts: 30,255
Likes: 37
Speedometer suddenly wacky
Sounds like your speedo head needs to be replaced. They do wear out. Sometimes a speedo shop can service it and make it last a bit longer.
When the needle starts fluctuating wildly, or stays at zero, or reads low, it is usually the cable that needs to be replaced.
In your case when it reads high it is usually a broken reaction spring, or the bushings are worn, or a piece of crud is in the mechanism. Worn bushings or dirt can cause more energy to be transferred by friction instead of magnetic coupling.
You can watch the odometer to see if it is still registering correctly even with the speed reading high. This will indicate a bad speedo head that needs service/replacement.
When the needle starts fluctuating wildly, or stays at zero, or reads low, it is usually the cable that needs to be replaced.
In your case when it reads high it is usually a broken reaction spring, or the bushings are worn, or a piece of crud is in the mechanism. Worn bushings or dirt can cause more energy to be transferred by friction instead of magnetic coupling.
You can watch the odometer to see if it is still registering correctly even with the speed reading high. This will indicate a bad speedo head that needs service/replacement.
Posting Guru
Joined: Sep 2001
Posts: 1,531
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From: in the country
Speedometer suddenly wacky
Eric , I'm fixing to finish the rebuild on np205----the plastic gear on the output shaft to the rear axle looks to be ok---should I put that special grease available at napa on the plastic gear before reassembling the last part of my xfer case ????fd
