The sticky about speedo gears... Flawed? - TCCoA Forums
 
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post #1 of 6 (permalink) Old 11-25-2015, 01:27 PM Thread Starter
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The sticky about speedo gears... Flawed?

Quote:
If you have an automatic with a 7-tooth output shaft (used on 94-97 Thunderbirds/Cougars, 93-98 Lincoln Mark VIII w/4R70W):
3.08 - 17 tooth, Green (C7SZ-17271-A)
3.27 - 18 tooth, Gray (C7SZ-17271-B)
3.55 - 20 tooth, Orange (C8SZ-17271-B)
3.73 - 21 tooth, Purple (D0OZ-17271-B)

If you have automatic with an 8-tooth output shaft (used on 89-93 Thunderbirds/Cougars w/AOD and all other 4R70Ws from other vehicles):
2.73 - 17 tooth, Green (C7SZ-17271-A)
3.08 - 19 tooth, Tan (C7VY-17271-A) for 225/60R16 ; 20 tooth, Orange (C8SZ-17271-B) for 215/70R15
3.27 - 21 tooth, Purple (D0OZ-17271-B)
Those are the same part number. The author hasn't been here since 2011 it seems, so I didn't try to contact him. The thread is also locked.

It looks like Steeda is the place to get speedo gears anymore.

http://www.steeda.com/mustang-speedo-gears/

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post #2 of 6 (permalink) Old 11-25-2015, 02:17 PM
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They're the same part number because they're the same part.

The 8 tooth calculations and 7 tooth calculations mean you will be using different speedo gears for the same rear end in most cases.

In general the gear to use with a particular final drive ratio in the sticky is correct, however you should run the formula with your specific tire size as well to ensure you aren't on the low or high side of a threshold between gears. E.G. with my tire size, 3.73s and a 7 tooth output shaft, my speedo is most accurate with a 20 tooth gear, NOT a 21.

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post #3 of 6 (permalink) Old 11-25-2015, 07:11 PM
No, Mr. Lemmywinks, No!!!

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Here's a good calculator:

http://www.sccoa.com/faq/speedgr.html

I'm running purple gears from PATC.com in my cars; I have '02 Gran Marquis transmissions in them.

Red '96 Cougar XR-7 240k mi. '02 4R70W, PST DS : '03 PI engine, 04 maf, 24lb injectors, 2.5" exhaust, '02 4r70w + Jmod, DirtyD0g TC + cooler + 3/8" lines, 255 walbro fp. Alpine system.
Black '96 Cougar XR-7 (Lazarus) 210k mi PI Intake, '02 4R70W, Jmod, PST DS, GrogTune, Konis, Mark LCA+Poly, racecougar Custom Engine Chain, and JL and racecougar Bracing.
Black '97 Tbird Limited Edition, '02 4R70W, 255 walbro, PST DS, PBR Brakes&SS lines, Toicko Blues & Springs, GrogTune.


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post #4 of 6 (permalink) Old 11-25-2015, 08:05 PM
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How many miles are you guys getting out of the purple gear before it gets chewed up? I think I only like 1,500 miles with mine
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post #5 of 6 (permalink) Old 11-26-2015, 06:51 PM
No, Mr. Lemmywinks, No!!!

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Quote:
Originally Posted by 1995 cougar xr7 View Post
How many miles are you guys getting out of the purple gear before it gets chewed up? I think I only like 1,500 miles with mine
I have never had one chewed up; I think you're thinking of the 23 tooth, it's made for a jeep, iirc.

The purple one in my bird was in the cougar for a few years, then got swapped with an orange one for a year, then the bird got swapped back to purple when I changed tires again.

I have a set of all of them, over the years.

I seem to have a ****load of tan and green ones; I bet they came in replacement transmissions, lol.

Red '96 Cougar XR-7 240k mi. '02 4R70W, PST DS : '03 PI engine, 04 maf, 24lb injectors, 2.5" exhaust, '02 4r70w + Jmod, DirtyD0g TC + cooler + 3/8" lines, 255 walbro fp. Alpine system.
Black '96 Cougar XR-7 (Lazarus) 210k mi PI Intake, '02 4R70W, Jmod, PST DS, GrogTune, Konis, Mark LCA+Poly, racecougar Custom Engine Chain, and JL and racecougar Bracing.
Black '97 Tbird Limited Edition, '02 4R70W, 255 walbro, PST DS, PBR Brakes&SS lines, Toicko Blues & Springs, GrogTune.


"War Is Peace. Freedom Is Slavery. Ignorance Is Strength." - George Orwell.
Truth Isn't Truth. - Rudy Giuliani, 2018 Award winner, “Most Outrageous Diversion” by MSNBC for this quote
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post #6 of 6 (permalink) Old 11-27-2015, 09:29 PM
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I've yet to ruin a 21-tooth purple gear either.

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