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Author
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Topic: speedometer is wrong now...
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68 Coop
Gearhead Posts: 4243
From: Mesquite, NV. 89027 M&M# 4256
Registered: Oct 2004
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posted 05-14-2006 10:57 PM
   
that I have my new rear gears, and I was wondering what to do to correct it? I'm not totally sure, but I think it's off around 10mph now, and it seems to be fast. Thanks for any suggestions.------------------
William
The easiest way to find something lost, is to buy a replacement. 68 Coupe
289
C4
3:55's/Trac-Lok
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68mustang351w
Gearhead Posts: 500
From: San Jose Ca
Registered: Sep 2004
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posted 05-14-2006 11:20 PM
Check this link The drive gear should stay at 7 (if the original rear end ratio was between 2.70 and 3.50 OR 6 if ratio was between 3.50 and 4.30*) and you are solving for driven gear... David F.* according to NPD catalog edit to add statement above [This message has been edited by 68mustang351w (edited 05-14-2006).]
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68 Coop
Gearhead Posts: 4243
From: Mesquite, NV. 89027 M&M# 4256
Registered: Oct 2004
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posted 05-15-2006 12:23 AM
Thank you, that's very informative. I didn't realize it was that much to it.
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zieber
Gearhead Posts: 102
From: Central Coast, CA, USA
Registered: Mar 2006
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posted 05-15-2006 01:24 AM
I don't know for sure if this calculator works but it is simpler.http://www.428cobrajet.com/speedo-calc.html
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68 Coop
Gearhead Posts: 4243
From: Mesquite, NV. 89027 M&M# 4256
Registered: Oct 2004
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posted 05-15-2006 01:41 AM
That one says I need an 8 with the 295 tires, so I'll just wait till I get my new tires and see what it says then. Thanks for the time and info.------------------
William
The easiest way to find something lost, is to buy a replacement. 68 Coupe
289
C4
3:55's/Trac-Lok
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68mustang351w
Gearhead Posts: 500
From: San Jose Ca
Registered: Sep 2004
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posted 05-15-2006 01:42 AM
quote:
Originally posted by zieber:
I don't know for sure if this calculator works but it is simpler.link
Just checked it and the calculator works but it assumes you have a 6 tooth drive gear. In order for it to be accurate, William (or anyone else with a 7 tooth drive gear would have to change both gears (drive & driven)... David F.
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68 Coop
Gearhead Posts: 4243
From: Mesquite, NV. 89027 M&M# 4256
Registered: Oct 2004
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posted 05-15-2006 08:06 AM
 Thanks David, I just want to get it right the first time, and do the easiest way possible. 
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68 S-code GT
Gearhead Posts: 3553
From: Sayreville, NJ, US
Registered: Mar 2000
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posted 05-16-2006 08:06 AM
This will help some with your RPMs. http://www.ringpinion.com/content/calculators/RPM.asp I know this has come up in the past (cause I asked about it once ) and there are a few formulas here somewhere but you have to find out what the outside diameter of your tires are. ------------------
Ed S. 68 S-code FB GT 4spd(now C6)/3.25 PS PDB
68 J-code(now 289) Cp Sprint"B" C4/3L00-9" PDB PS AC Bla-Bla-Bla
99 F150 XLT Ext/cab, 4X4, 5.4L, 3L55
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68 Coop
Gearhead Posts: 4243
From: Mesquite, NV. 89027 M&M# 4256
Registered: Oct 2004
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posted 05-16-2006 09:18 PM
Thanks Ed.I have 26.5 OD(P295/50R 15) on my back tires, and they are bigger than the front, so I take it I go with the biggest tire??? [This message has been edited by 68 Coop (edited 05-16-2006).]
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68mustang351w
Gearhead Posts: 500
From: San Jose Ca
Registered: Sep 2004
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posted 05-16-2006 09:27 PM
You always go with the rears because those are the ones that are doing the pushing of the car... David F.
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68 Coop
Gearhead Posts: 4243
From: Mesquite, NV. 89027 M&M# 4256
Registered: Oct 2004
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posted 05-16-2006 09:47 PM
 Thanks David, just wanna be sure about this .
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68mustang351w
Gearhead Posts: 500
From: San Jose Ca
Registered: Sep 2004
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posted 05-17-2006 01:16 AM
No problem, thats what we are here for.... David F.
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