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1981 speedometer problems

Old Sep 23, 2014 | 11:55 AM
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Default 1981 speedometer problems

I have a 1981 and am having speedo trouble. I replaced everything from the tranny up and it all works when I hook a drill and spin the cable at the tranny. I took the plastic gear out of the tranny and it is not stripped where the cable goes in or the gear itself. Any suggestions? Original problem was caused by the transducer locking up and breaking the lower cable. I replaced the lower cable and it worked for about 60 mile before transducer locked up completely. Lower cable was ok second time. Replaced both cables and transducer. ???
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Old Sep 23, 2014 | 12:41 PM
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can you look in the hole where the driven gear goes to see if the drive gear is stripped or has moved?
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Old Sep 23, 2014 | 12:56 PM
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No, I haven't looked in yet. I ran out of time and had to get it to my paint guy to touch up a spot. It has to be that internal gear I would think, but I can't imagine that the internal gear is plastic. The end of the plastic gear was not worn or marked up at all. If the internal gear is stripped I would think it would have marked the plastic gear. I'll take a peek inside when it comes back. Hoping its nothing too involved, getting the car ready to sell.
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Old Sep 23, 2014 | 01:32 PM
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The inner gear is plastic also. Probably when the transducer locked, may have damaged drive gear. Easier to try new driven gear first. I went thru the same problem.
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Old Sep 23, 2014 | 02:29 PM
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Thanks for the info. If the internal gear is plastic too, then that makes sense. Was it hard to change?
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Old Sep 23, 2014 | 03:16 PM
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Originally Posted by suspensionbuilder
Thanks for the info. If the internal gear is plastic too, then that makes sense. Was it hard to change?
Depends on the trans. Have to remove tailshaft to replace gear. Mine is a 4-speed and it was easier to remove trans completely. That's why it would be easier to try new driven gear first. Both mine looked fine.
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Old Sep 24, 2014 | 01:40 PM
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He probably has the TH 350C automatic transmission in his '81.

I have an '81 also. When I changed my rear axel gears I had to change the speedometer gears to correct the speedometer. I've changed the internal gear a couple of times. You have to take the rear tail piece off of the transmission. It can be done with the transmission in the car.

Get some extra clips that hold the gear on to the tail shaft. They are easy to break.

Last edited by Street Rat; Sep 24, 2014 at 01:49 PM.
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