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| | | Joined: Mar 2017 Posts: 53 'Bolter | | 'Bolter Joined: Mar 2017 Posts: 53 | In my 49 GMC I am using the original speedometer with a 700r4 trans. The speedometer reads approx. 68 when I'm going 60. And the odometer reads 6.5 miles traveled when I have actually gone 5.
The trans has a blue 38 tooth driven gear and a greyish drive gear that I can't count the teeth on.
I read somewhere that each tooth change on the driven gear will change the speedometer reading by 2 mph. More teeth slows the reading and less teeth increases the reading. If this is correct then I would need to install a 42 tooth driven gear. Does anyone know if the grey drive gear can handle the change to 42 or do I need to change the drive gear also? and if so to what and then what driven gear would I use as this would change the overall ratio.
Does anyone know what rpm the speedometer shaft has to turn to have the speedometer read 60mph? This might help me sort this out.
Tom | | | | | Joined: Jun 2004 Posts: 8,597 Riding in the Passing Lane | | Riding in the Passing Lane Joined: Jun 2004 Posts: 8,597 | The housing that the driven gear goes in has the gears number of teeth that can be used with that housing printed on it. About 4or 5 different gears can be used in that housing. I have used plus or minus one also. That may be confusing but clean off the face of the housing & you will see what I mean'
Speedos are calibrated 1000 revs. per mile.
George
They say money can't buy happiness. It can buy old Chevy trucks though. Same thing. 1972 Chevy c10 Cheyenne SuperIn the Gallery Forum | | | | | Joined: Apr 2005 Posts: 2,832 'Bolter | | 'Bolter Joined: Apr 2005 Posts: 2,832 | Do a search on "speedometer drive,driven gear calculator" and the TCI Automotive site will come up. Their formula is one that anyone with third grade math can use.
Evan
| | | | | Joined: Sep 2019 Posts: 223 'Bolter | | 'Bolter Joined: Sep 2019 Posts: 223 | Public or private school? | | | | | Joined: Feb 2001 Posts: 4,095 'Bolter | | 'Bolter Joined: Feb 2001 Posts: 4,095 |
Ron, The Computer Greek I love therefore I am.1954 3100 Chevy truckIn the Gallery 2017 Buick Encore See more pix1960 MGA Roadster Sold 7/18/2017
| | | | | Joined: May 2009 Posts: 85 'Bolter | | 'Bolter Joined: May 2009 Posts: 85 | Public or private school? That is Funny
1949 3100
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