I did a search on the speedo calibration and most of the topics assume the speedo was working. I recently bought my 69 camaro and it originally came with a small block and auto transmission. The previous owner swapped in a big block and T-10 transmission. When I bought the car, the speedo was not working. I bought a new cable and hooked it to the speedo and it seems to be working, so I checked the tranny end and found the teeth on the driven gear are stripped. So now the question. I have a 4.10 rear end with 27.5 inch tires. The T-10 transmission currently has a white drive gear. What is the correct driven gear? Sorry for the long build up prior to the question.

thanks
Dean

You may have to count the teeth on the white drive gear then go to the following site, use the formula and you should be set. Keep in mind that your white drive gear may not be the correct one for your current setup. http://www.chevelles.com/shop/speedo.html


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Robert

'69 getting better every day... (every pay day)

If memory serves me correctly, 4.10 and above ratios had a reducing gear box attached to the ext housing and then speedo cable hooked up to it.

I need one but haven't found any. The gear needed for our ratio would be too large to fit into hole of ext housing.

If you find one, let me know.

Everett 68/350/PG/11.90/115mph

Robert, I was looking at Ricks First generation catalog and they show the white driving gear, but they do not say how many teeth it has. Since the tranny is still in the car, it is a bit difficult to count the teeth. Any idea on the number of teeth? I checked the site you suggested. Definitly some good info.

Everett, Where did you hear that we needed a reducing gear box? Not questoning that we need it, just curious of the source. Thanks for the help so far.

bilydean

Sorry I don't know the answer. I bet someone on this site does though, if they happen to see this post. I was able to count the teeth on my automatic by pulling out the driven gear housing, jacked up the rear, with a flash light in hand I marked the first tooth then had my wife slowly turn the rear wheel as I counted. Counted about three times to make sure.

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Robert

'69 getting better every day... (every pay day)

From the GM Parts man himself, He suggested GM put them on by application.

He also said hasn't seen much activity for them either, But he did know what I was talking about and remembered them from the Wayback Machine

Everett 68/350/PG/11.90/115mph

Well, I finally have the solution and my speedometer is working and actually reading correct. I put in a 24 tooth driven gear and that was about as big as I could fit in and that still wasn't correct. What I finally ended up with was a 22 tooth driven gear and then used the adapter, part number 3932220, which is a gear reduction of 1:0.75.
This equates to roughly adding 5 teeth to the driven gear. Everett, you were right.

thanks
Dean

Thanks, Dean for the P/N of the reducing box.

I knew my memory wasn't that far off. I called my GM parts man to check on pricing, $30 each.

Everett 68/350/PG/11.90/115mph

Everett, just so you know, this is a straight adapter, not a 90 degree.

Dean