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04-14-2008, 03:27 AM | #1 |
Oilfield Trash
Join Date: Sep 2003
Location: Raymore, Sk, Canada, Earth
Posts: 3,171
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Speedo Gear Calibration
I'm finally getting around to makin my speedo read correctly, I found on this site http://www.transmissioncenter.net/sp...n_______va.htm what gear combos i need, just wondering what "speed" the speedo in these trucks is. It says on the site most speedo's 1965 and up read at 1000 revs per mile, is this true for a 72 truck? BTW, its 700r4 trans, 3.73's, and 28 inch rubber.
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14 Dodge 3500 Mega Cab 08 Dodge 3500 Mega Cab 87 Chev 3+3 4x4 80 GMC K10 High Sierra bone stock 70 Chevelle 350SS long term project 68 GMC 3ton Grain Truck/Garbage wagon 50 Pontiac 2 Door Coupe Project "I've got a shotgun rifle and a 4 wheel drive and a country boy can survive" Hank Jr. |
04-14-2008, 06:07 AM | #2 |
The Older Generation
Join Date: Aug 2006
Location: Montezuma, Iowa
Posts: 25,591
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Re: Speedo Gear Calibration
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I'm not close to a speedo to look but this site says some are marked in small numbers at the bottom of the face. http://www.bgsoflex.com/speedo1.html LockDoc
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Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 - |
04-14-2008, 03:36 PM | #3 | |
Senior Member
Join Date: Apr 2005
Location: Joppa, Maryland
Posts: 4,408
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Re: Speedo Gear Calibration
Quote:
The gears you need are: Speedo driven gear 40 tooth (black) drive gear 15 tooth (gray) The "driven gear is where your speedo cable fits into & the drive gear is in the tail shaft. You have to remove it to replace that gear. Check your colors though, you might already have the gray gear in there, & you'll only have to change the speedo gear. http://www.bgsoflex.com/speedo1.html
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1997 GMC Sierra Ext 1965 Mustang Last edited by 70GMCer; 04-14-2008 at 06:04 PM. |
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04-14-2008, 06:52 PM | #4 |
Registered User
Join Date: Oct 2005
Location: Overland Park, Ks.
Posts: 5,226
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Re: Speedo Gear Calibration
The 700-4R trans. is easy to calibrate the speed. Compare the odometer with the mile markers on the freeway. If it gains tenths take out the driven gear & get one with more teeth. If it looses get one with fewer teeth.
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04-14-2008, 08:15 PM | #5 |
Senior Member
Join Date: Apr 2005
Location: Joppa, Maryland
Posts: 4,408
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Re: Speedo Gear Calibration
It depends if the driven gear fits within the drive gears range. Mine didn't and had to change to get the correct ratio. It's a lot easier to do the calculator method, rather than buying different gears until you get it right. $2 a piece at GM
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1997 GMC Sierra Ext 1965 Mustang |
04-14-2008, 09:46 PM | #6 |
Oilfield Trash
Join Date: Sep 2003
Location: Raymore, Sk, Canada, Earth
Posts: 3,171
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Re: Speedo Gear Calibration
ive never changed the speedo gears before, but i do know what has to be done, except, is there any special procedure for makin the gears mesh correctly?
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14 Dodge 3500 Mega Cab 08 Dodge 3500 Mega Cab 87 Chev 3+3 4x4 80 GMC K10 High Sierra bone stock 70 Chevelle 350SS long term project 68 GMC 3ton Grain Truck/Garbage wagon 50 Pontiac 2 Door Coupe Project "I've got a shotgun rifle and a 4 wheel drive and a country boy can survive" Hank Jr. |
04-16-2008, 02:41 PM | #7 |
Senior Member
Join Date: Apr 2005
Location: Joppa, Maryland
Posts: 4,408
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Re: Speedo Gear Calibration
That's why you have to be within a certain range for the gears to mesh. When they are within that range, they just couple together in side the case. If the two gears are out of that range, they will just bind up and strip, and most likely break into pieces.
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1997 GMC Sierra Ext 1965 Mustang |
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