TH350 Jumping/Erratic Speedo - Chevy Nova Forum
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Old 19th-November-2012, 07:43 PM   #1
65Coupe
 
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Question TH350 Jumping/Erratic Speedo

Hey guys, I'm trying to figure out a jumping speedo issue that's getting worse. I thought it was the mechanical cable, and the problem would go away when I recently switched to an electronic speedo with SN16 pulse generator. Still the same problem with the electronic speedo. I just inspected the gear that inserts in the tail shaft, both the teeth and inner square bore that turn the sensor are fine. Could there be an issue with the gear on the tail shaft slipping? I peaked in the trans at the gear isn't stripped or anything, so I'm not sure what's going on. Any advice? Thanks.
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Old 19th-November-2012, 09:09 PM   #2
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Have seen the drive gear in the trans slip. There is a metal retaining clip that holds the drive gear in place! The bad you have to remove the tailshaft housing pretty easy fix though!
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Old 19th-November-2012, 09:18 PM   #3
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Can you spin up the pulse generator with a drill or something to see if it still jumps? Might help you eliminate some possibilities...

Good luck!
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Old 19th-November-2012, 09:23 PM   #4
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I put a drill on the signal generator, speedo works just fine with no jumping around...so it's got to be in one of the gears. I noticed quite a bit of play in the gear shaft that fits into the bullet, almost like the bullet is worn. I'm wondering if this could allow the gear to disengage intermittently from the tail shaft gear. I'll try a new bullet and gear first before I go removing the tail shaft assembly. Hopefully the local trans shop carries the bullet?
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Old 20th-November-2012, 06:56 PM   #5
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Quick update, installed a new steel bullet and plastic 22 tooth gear today and the speedo is reading better but is still jumping around +/- 5 mph. Only thing left to replace us the tail shaft gear.
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Old 21st-November-2012, 09:54 AM   #6
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The clip coming loose is a very common problem. When you replace the drive gear get a new clip just in case.
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