transmission speedo gear
I am trying to determine the correct specs. for the speedo gear
for a Muncie 21, 3.55 ratio rear , with 205P70X15 tire Thanks in advance for any info.
for a Muncie 21, 3.55 ratio rear , with 205P70X15 tire Thanks in advance for any info.
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Re: transmission speedo gear
Since your tires have a few percent higher revs/mile than the OE tires, your speedo may be more accurate using the driven gear for the 3.70 axle, which I think is 22T. The 3.55 axle driven speedo gear is 21T.
The OE tires are 775 revs/mile. You can look up the specs for your 205/70R-15s on the mfg's. Web site, or use any other tire of the same size since the spec is very close for all tires of any given size regardless of brand or model.
Duke -
Re: transmission speedo gear
Duke and Jerry-----
For 1969 with original F70-15 tires the speedometer driven gear was 22 tooth for 3.55:1 and 23 tooth for 3.70:1. The revs/mile of a 205-70-15 tire is about 790/mile or about 2% greater than the original. I think the 22 tooth gear would likely be the closest you're going to get without using a custom-calibrated speedometer adapter. However, WHICH 22 tooth gear (GREEN or SILVER) is the question. That depends upon which speedometer DRIVE gear is currently installed in the transmission. DRIVE gears are hard to get at but the gear can be inferred from the color of the DRIVEN gear that's in there now.In Appreciation of John HinckleyComment
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Re: transmission speedo gear
Here is the raw info on speedo gears
New OEM AC Delco gears are used in Muncie, GM T10, GM Super T10, Saginaw 3 & 4 speed, GM T5, Powerglide, 200 & 350 transmissions.- 17 tooth purple dimension -1.75 x .305 x .810
- 18 tooth brown dimension -1.75 x .305 x .810
- 19 tooth white dimension -1.75 x .305 x .810
- 20 tooth blue dimension -1.75 x .305 x .810
- 21 tooth red dimension -1.75 x .305 x .810
- 22 tooth grey dimension -1.75 x .305 x .810
- 17-22T .810 diameter gears must be used with a 1.84 OD speedo drive gear.
- 22 tooth green dimension -1.75 x .305 x .870
- 23 tooth black dimension -1.75 x .305 x .870
- 24 tooth yellow dimension -1.75 x .305 x .870
- 25 tooth orange dimension -1.75 x .305 x .870 - NO LONGER AVAILABLE
- 22-25T .870 diameter gears must be used with a 1.76 OD speedo drive gear. Speedo Gear ChartAxle Ratio 6T 7T 8T -Drive Gears2.73 - - 18 3.08 - 18 203.27 - 19 213.55 17 20 223.73 18 21 234.10 19 22 244.30 21 23 254.56 23 24
- Calculated driven gears are based on normal 26" tires and the formula listed below:
Driven Gear Teeth = Drive gear teeth x axle ratio x tire revs/mile
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