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Old 05-02-2012, 04:30 PM
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Speedometer gear

Hello all! New to the forum and almost finished my 23 T. I've been on here reading many posts over the last year and a half of the build and want to thank many of you for your expertise. Of course I didn't post just to say thanks . I have a TH400 in my T and trying to match a speedo gearset. I currently have a black speedo gear and green drive gear. I have a 2.73 with 26.5 in tires in the back. Two questions to keep me from pulling my hair out:

1. What ratio would you recommend?
2. Do I need to replace the drive gear if I replace the speedo gear with one that required the 36-39 housing (40 tooth to a 34 tooth for example)? I have both housings 1362077 and 1362076 but the gear diameters are different (1.7 and 1.5" respectively).

Thank you for any help and glad to be part of the Hot Rodding community!

Troy

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Old 05-02-2012, 07:25 PM
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Here's the easy way. Put in which ever combo you want. Test drive against a gps or another vehicle at 60mph and buy an adaptor to adjust your speedo.
http://www.ebay.com/itm/Gear-Ratio-A...4708d1&vxp=mtr
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Old 05-02-2012, 09:04 PM
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Quote:
Originally Posted by Dtimekw
Hello all! New to the forum and almost finished my 23 T. I've been on here reading many posts over the last year and a half of the build and want to thank many of you for your expertise. Of course I didn't post just to say thanks . I have a TH400 in my T and trying to match a speedo gearset. I currently have a black speedo gear and green drive gear. I have a 2.73 with 26.5 in tires in the back. Two questions to keep me from pulling my hair out:

1. What ratio would you recommend?
2. Do I need to replace the drive gear if I replace the speedo gear with one that required the 36-39 housing (40 tooth to a 34 tooth for example)? I have both housings 1362077 and 1362076 but the gear diameters are different (1.7 and 1.5" respectively).

Thank you for any help and glad to be part of the Hot Rodding community!

Troy
The rear gear ratio depends on a few things like the weight of your rod and the powerband of the camshaft. Also important is how you drive- whether acceleration is more important than 'comfortable' HW cruising.

That said, I would guess a ratio equal to or higher (lower numerically) than 3.73 would work well for many applications. But to get any closer than that will take more info.

Here is a link that might help; be sure to follow the link to the Speedometer Calculator.
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Old 05-03-2012, 08:35 AM
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Thanks for the info. I like the way the car is set up now with the rear gears and tire size. I am looking more at the speedo gears to calibrate the speedo. My biggest question is whether or not I need to change the drive gear on the tailshaft when I change from a large gear (40 tooth) housing to a smaller gear (34 tooth) housing. The driven gear diameters are different and the 34 tooth gear (1.5" diameter) doesn't mate with the drive gear. It looks like I need to replace the drive gear but not sure which ratio (or diameter)I should go with on my set up. Any ideas or suggestions?
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Old 05-03-2012, 09:09 AM
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As I remember each tooth is about three mph
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