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06-04-2018, 11:13 PM | #1 |
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Join Date: Jan 2007
Location: Garland,TX
Posts: 431
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Speedometer calibration
I ordered a 22 tooth driven gear for my speedometer cable and according to my gps it reading about 10 mph too fast. I ordered the gear based on the online calculators I found.
The drive gear is 8 teeth, 3.73 gears, and 26.6" tall tires. So would I order a gear with less teeth to try and get it more accurate? I figured less teeth would mean slower turning.
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80 C10 SWB Step Side - 350 w/ vortec heads, TH350, 12-bolt 3.73 |
06-05-2018, 09:48 AM | #2 |
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Join Date: Jan 2018
Location: MEDICINE HAT
Posts: 77
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Re: Speedometer calibration
If its reading too fast you need a driven gear with more teeth. All the calculators are fine but usually it comes down to having a handful of driven gears and just keep trying till you get as close as you can.
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06-05-2018, 03:15 PM | #3 |
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Join Date: Aug 2012
Location: Oklahoma City, OK
Posts: 2,611
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Re: Speedometer calibration
Yep. If the drive gear has 8 teeth, it will move the driven gear 8 teeth for each rotation of the drive gear. More driven teeth, slower rotations.
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06-05-2018, 06:13 PM | #4 |
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Join Date: Jan 2007
Location: Garland,TX
Posts: 431
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Re: Speedometer calibration
It looks like it jumps from 22 to 34-45. I assume I'll have to change the drive gear as well if I go with the 34-45 gears. It appears I'll have to try one of the 17+ drive gears. If I go that route, I read that I need a different speedo bullet for the driven gear.
Man, its too hot in Texas right now to be dealing with all this mess! HAHA!!
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80 C10 SWB Step Side - 350 w/ vortec heads, TH350, 12-bolt 3.73 |
06-05-2018, 09:42 PM | #5 |
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Join Date: Oct 2008
Location: Wentworth, NH
Posts: 4,977
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Re: Speedometer calibration
Download the 79-84 parts books. I scanned all of the parts books for the 73-93 Squares and the 88-93 T400 chassis.
No need to guess... There are tables in each set of books that tell exactly what drive and driven gears GM used based on model year, 1/2 3/4 & 1ton, tire size, axle-ratio, and what transmission/transfer-case is in it. The parts book tables also tell if you need to run a ratio adapter and the GM part numbers for those too. If you're running a transmission or transfer case that GM didn't use in 1980 just use the year that trans or TC was used as your model year.
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1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...
And please let us know if and how your repairs were successful. Last edited by hatzie; 06-05-2018 at 09:48 PM. |
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