Jumping speedometer
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Senior User
Joined: Jan 2007
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From: Norheimsund, Norway
Jumping speedometer
My speedometer started to act funny today. It shows a lot more than my actual speed, and is jumping up and down. Anyone who has been through this before and can tell me how to fix this?
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Joined: Nov 2012
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I had a problem with the speedo and odometer malfunction as you stated, founf the problem in the ground wire from battery to the body. Replaced the bolt that holds all the wires and problem solved. Sand the body part with sandpaper or emery cloth also the ends of the wire connectors.
Lead Driver
Joined: Mar 2006
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From: western SD
You 91 should have a mechanical driven speedo, driven by a plastic gear on the output shaft of the tranny, if 2wd. If you have a 4X4 that gear is in the transfer case.A lot of times the plastic gear wears a concave in it where the speedo cable gear runs against it, letting the cable gear skip over the teeth of the drive gear causing the needle to read all over the place. The fix is usually a new plastic gear for the tranny. If you pull the speedo cable from the tranny, you will see a small plastic gear on the end of the cable. This gear can go bad, but it is rare. The cable can become sticky from the lube becoming old inside the "tube" that the cable runs in, sometimes a good cleaning and relubing it will help, but I would bet that the dive gear in the tranny is worn.
Lead Driver
Joined: Mar 2006
Posts: 5,111
Likes: 1,544
From: western SD
You could try lubing the cable by removing the end from the dash, and hosing it with some penitrating oil, this might help. If the gear in the transfer case is bad, the case has to be opened up. You probably have the Borg Worner 1356 case on your truck. I would think a place that handles Borg Woener would be able to get the gear. The gears are color coded ( blue, green, yellow, ect.) be sure to get the same color gear as is in the case, as the different colors have different tooth counts, and will affect the way the needle reads.
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