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Old 06-16-2003, 04:38 PM
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th350 speedometer problem

Had my 77 vette TH 350 rebuilt this past winter, speedometer worked fine for awhile and then quit? Can turn cable at trans by hand and it moves the needle but when hooked to the trans, nothing?? Pulled the gear out of trans. and hooked up cable & turned gear by hand and needle moves. Anyone have any ideas whats wrong??

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Old 06-16-2003, 04:47 PM
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There should be a plastic drive gear inside the transmission hole. The gear is held in place by a metal clip. I have seen these gears move off of the clip, causing the speedo to quit working. Check and see if you can see the gear inside the hole. If you can see it, see if you can move it with a screwdriver or something like that. It may move a little, but not much. It also should not spin on the shaft. If it moves, or did move, you need to remove the extension housing and put it back in place with a clip. The clip fits in a hole in the shaft and the gear slides over it to lock in place.
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Old 06-16-2003, 05:42 PM
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Thanks for the info, but what is the extension housing??? I can insert a cable where the speedometer cable screws on and turn it. Does this mean the gear is off inside the trans.???
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Old 06-17-2003, 12:07 PM
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Extension housing = tailshaft housing. It's the rear-most section of the transmission, the driveshaft yoke slides into it.

You might be able to see inside the speedo hole with a small mirror & flashlight. Look for a gear on the tailshaft with spiral teeth that are almost perpendicular to the tailshaft. It's about 3/4" thick. If you can see it, try to move it back & forth with your finger or a screwdriver. It should move only a little bit. It should not turn on the shaft. If all you see is a raised flat section of the shaft, you must remove the tailshaft housing to fix it.

Last edited by jimfulco; 06-17-2003 at 12:16 PM.
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Old 06-17-2003, 06:38 PM
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Thanks again, it was what you said, This was on a 77 vette and it didn't take as long or as hard as I thought (about 1 hour). Its back working again. Thanks; jw
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