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Speedometer drive gear stripped


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I'm wondering if anyone could provide some insight in to this. I got this 1962 Lesabre about 1-1/2 years ago. The speedometer didn't work. It wasn't high on the priority list so I didn't really bother with it until this Summer. 

 

There was no drive gear in the transmission. I ordered one and installed it. The speedometer worked perfectly for 13.2 miles and then quit. I pulled the gear to check it out and the teethe are almost completely gone. I'm sure not going to order another $100 gear until I can sort this out. The speedometer moved smoothly and I couldn't feely any resistance in the cable. I Also recently had the trans pan cleaned out. he said he didn't find any debris in there. 

 

 

Anyone? 

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Here are pictures. Obviously after the gear was destroyed.  I believe it is the driven gear. Yes, it looked like the ones above. I would imagine the only way to get to the drive gear is to disassemble the transmission. I'm going to try to stick my finger in there and see if I can feel anything on the internal gear. Before I installed this, I turned the speedometer cable with a cordless drill. There was no noise and the needle moved smoothly for the 13 miles that the speedometer worked. 

 

 

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20190715_184022.jpg

Edited by drhach
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3 hours ago, drhach said:

I'm going to try to stick my finger in there and see if I can feel anything on the internal gear.

Get a bore scope to look at the drive gear:  less than $40 to use with your smart phone.

That way you don't have to tear it apart to get the diagnosis and then wait on parts.  In the meantime use your gps as a speedometer and odometer and drive it!

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That's  a great suggestion. I think harbor freight sells a pretty cheap model. I'm certainly driving it anyway. I just want to get all systems operational. I'm cheap enough and enough of a nerd that I'm looking in to making a speed sensor that would run the speedo cable. 

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2 hours ago, drhach said:

That's  a great suggestion. I think harbor freight sells a pretty cheap model. I'm certainly driving it anyway. I just want to get all systems operational. I'm cheap enough and enough of a nerd that I'm looking in to making a speed sensor that would run the speedo cable. 

 

 There  is one out there.

 

  Ben

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Gm transmissions use two different size driven gears depending on the rear end ratio. The problem I had with my camaro was I needed a 19 tooth drive gear but my trans had a small diameter driven gear so the teeth didn't mesh hence the Speedo didn't work. It is possible that you have a large diameter driven and drive gear and that caused the teeth to be destroyed?  Was it difficult to install the drive gear? 

Bruce 

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There actually are two companies selling speedo cable drivers. Both of them are well over $300. I'm thinking I can make my own for much less than that. I just bought an Arduino controller board for $12, I need to get a DC motor and figure out some way to mount a sensor for a square wave output. 

 

I may have bought the wrong size gear. I checked my speed against a GPS and it was pretty good. The repair manual actually has a table telling you what size gear to use based on rear end ratio. 

 

I talked to the guy I bought the gear from (bestoffercounts). He suggested a few checks I could do. Mainly validating that the core spins freely and the bushing on the back of the speedo isn't sticking. So that and a bore scope are my next steps. 

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