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01-08-2003, 05:39 PM
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#1 |
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Workaholic
Join Date: Oct 2002
Location: Katy, TX
Posts: 1,589
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Speedometer gears
Does anyone know how many MPH each tooth on the speedo gear changes? I haven't pulled my gear out yet but my speedo is now 15 MPH slow so when I pull my gear out I need to know how to calculate which new gear I will need.
Thanks
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1979 K-10 Silverado (work in progress) 1991 V1500 Subruban 1999 Suburban LT 4x4 2006 Suburban LTZ (daily driver) |
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01-08-2003, 08:10 PM
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#2 |
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Gentleman Jim Driver
Join Date: Nov 2002
Location: Poulsbo, WA
Posts: 1,553
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Its not always 15mph slow. Having the wrong speedo gears will throw your speedo off by a percentage at all speeds. For example, if you have a 35 tooth driven gear but need a 37 tooth, your speedo will be off by 2/35 or 6% fast. More teeth on the gear will slow down the speedo drive, less will speed iit up.
This site worked for me to calibrate my speedo in my 87. http://www.chevelles.com/shop/speedo.html
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Joe '75 GMC Gentleman Jim '84 Chev C10 Short Wide - Super duper plain (manual steering, manual brakes, no dome light, no cig lighter) '85 Chev C10 Short Wide - Super plain Vortec 4.8 4L60E trans also: '81 K30, '83 C30 Crew Dually, '84 M1028 CUCV, '85 M1009 CUCV, another '85 C10 SWB, '89 R3500 Flatbed |
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01-08-2003, 08:28 PM
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#3 |
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You get what you pay for
 
Join Date: Dec 1999
Location: Cherryville, NC
Posts: 4,798
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Mike 1985 Chevy C-10 |
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01-09-2003, 06:01 PM
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#4 |
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Workaholic
Join Date: Oct 2002
Location: Katy, TX
Posts: 1,589
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I have no idea what size tires originlly came on the truck so I used the formula to find the right gear combo. Someone double check this before I go and buy the gears.
[18 t drive gear*3.42*(20168/35)]/1001=35.43~35 t driven gear My tires actually measure 34.5 but I thought I'd put in 35 so I would run just a tad on the slow side since I tend to speed anyways.
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1979 K-10 Silverado (work in progress) 1991 V1500 Subruban 1999 Suburban LT 4x4 2006 Suburban LTZ (daily driver) |
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01-09-2003, 07:39 PM
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#5 |
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Gentleman Jim Driver
Join Date: Nov 2002
Location: Poulsbo, WA
Posts: 1,553
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35 or 36, either would be very close. 18 Teeth makes the teeth on the drive gear very small, but I don't think you have any other choice.
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Joe '75 GMC Gentleman Jim '84 Chev C10 Short Wide - Super duper plain (manual steering, manual brakes, no dome light, no cig lighter) '85 Chev C10 Short Wide - Super plain Vortec 4.8 4L60E trans also: '81 K30, '83 C30 Crew Dually, '84 M1028 CUCV, '85 M1009 CUCV, another '85 C10 SWB, '89 R3500 Flatbed |
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01-09-2003, 11:18 PM
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#6 |
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BAD BOW-Silverado XST
Join Date: May 2000
Location: Senior Member from Austin, TX
Posts: 6,431
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Don't like math?
Try website for the gears. Just keep playing with the number of the drive gear until you find a driven gear that is closest to a whole number. Then just take the part numbers to a dealer or tell them the tooth numbers. |
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