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This is a bunch of speedo gears I purchased at the Louisville, KY swap meet today and I thought it might be useful for those of you who have speedometer error caused by switching to a different size tire diameter or different rear axle ratio. This is the part needed to fix that.

The two pale green colored gears on the right are for a Four Speed transmission. Notice the teeth slant the opposite direction of the ones on the left which are for automatic transmission such as C4 and C6.

The five gears on the left are:
21 tooth (red),
20 tooth (black)
17 tooth (white)
16 tooth (maroon)

The stock application chart uses tire sizes which are useful as a reference but since they are all bias ply 14 inch tires they are not a whole lot of help unless you have reproduction bias ply tires.

To illustrate what works, I have 3.50 gears and 215/70R-14 tires on my green GTE and the speedo is accurate. It has the black 20 tooth gear installed.

I have 2.75 gears in the blue GTE with 215/70R14 tires in the blue GTE and the speedo is accurate with an 18 tooth gear.
 

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Vendor?

Royce do you know of any vendoes that will be in Columbus that sell them?I will need a few
 

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Discussion Starter #4
Stillwells Mustang and John's Classic Cougars are always there. You might tell one of them ahead of time to bring you a selection of speedo gears for your application.
 

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Nice find Royce.....looks like you did better than I. If you don't need the black one I'll be happy to take it off your hands for a small fee.
 

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Hey Royce, great info. I would take both 4-speed gears off your hands if you don't need them. Let me know and thanks.
I am still trying to find the right gear for my cat.
 

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Hey, these are for my permanent collection. I have enough Cougars and rear end ratios to warrant keeping this collection for future use!

The guy selling these parts was a former Louisville Ford plant employee selling off things that accidentally came home with him. I paid $35 for the whole bunch. That's half what the vendors get.
 
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no problem Royce....when you said you thought they might be usefull to us in your original post I thought that you were looking to resell. Catch you later!
 

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Speedo Gears

I think that the driven speeodometer gears are still available at Ford dealers also. Some dealers also stock them. The price is also reasonable
 

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Interesting. I use a 20 tooth gear with a 3.25 rear-end and my speedo is accurate. That is with 215-70-14 tires. I would think a 3.50 rear would need a 21 tooth speedo gear, with a diamter of just under 26". I think Rick Dempsey and I came up with the same numbers, the last time we had this conversation.

Check out the following website for a neat speedo gear calculator:

http://www.ffcobra.com/FAQ/speedo.html
 

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Factors here are tire diameter, different brands the same size are different diameters.
 

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What is the difficulty of installing a new speedo gear and do you guys have any helpful tips? (i.e. is it easy to break anything else in the process?)
 

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KEY DIFFERENCE BETWEEN GEARS!

Royce,

One thing you failed to mention is the fact that there are "short" and "long" gear snouts. Yours appear to be short. The long are needed for FMX,C6,AOD on a factory automatic car.

A factory 3 speed car uses the same rotation gear but a different speedo cable and different length snout gear.

A factory 4 speed car uses the reverse rotation (shorter?) gear.

The gear sections are identical in length -- the snouts change.

Been down this road already!
 

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Discussion Starter #15
Bill,

In 1967 - 68 there are no Long Snout gears.

The ones shown are correct for C4 / C6 or (opposite rotation) 3 and 4 speed manual trans for 1967 - 68.

Looking in the Lincoln Mercury Master Parts Catalog, Page 2 of section 172 we see that all the gears I have can be identified as either Type 3A or Type 3C. These are short snout. Further investigation of a specific application shows:

Page 2, Section 172.66
Application = 1968 390 / C6Auto
Tire Size = 8.45X15
Gear Ratio = 3.25
Driven gear P/N = C0DD 17271-C
Back to the identification tables, this gear type is 3A, 19 tooth short shaft. A quick look at the application page reveals the same gear is usedwith a C4 application. Notice the tall tire size, the chart is poor when it comes to selecting a gear to use with Cougar sized 14 inch tires.

I had never seen a long snout gear in person, only the illustration in the MPC. I reverse cross checked one of the part numbers and found it is used in later Cougars with automatic transmissions. This would necessitate internal changes in the transmission so a later transmission in a 67 - 68 would need this also.

The long snout version (Type 3) is used beginning in the 1969 model year in Cougars and other Ford / Mercury Products with automatic transmission. It appears that the introduction of the FMX transmission might be the reason, I don't know for sure. Three and Four Speed manual transmissions continue to use the short nose gear even in later years according to the Master Parts Catalog.

So with regard to 69-70 model year Bill you are correct, the long snout gears are for automatic applications.

I learn something new every day!
 

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Good info

Cool! I didn't realize there was difference either! Thanks for the info.
 

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Ford SVO catalog info

In fact I'll ping the local Ford tranny guy -- I think you know him -- and ask him what the scoop is. On the '88 AOD that I put in it came with the long snout gear. The '70 Elim 3-spd car I had was a short black gear.

Here are the part numbers Ford (SVO Racing) is calling out for the automatic cars. See if they line up:

D0AZ-17271-A = BLUE, 16 tooth
C7SZ-17271-A = GREEN, 17 tooth
C7SZ-17271-B=GRAY, 18 tooth
C7VY-17271-A=TAN, 19 tooth (my factory FMX, 3.00:1 gears)
C8SZ-17271-B=ORANGE, 20 tooth
D0OZ-17271-B=PURPLE, 21 tooth

These are still over the counter according to SVO.
 

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Discussion Starter #18
Gear types

Bill,
I looked in the Master Parts Catalog and found that they are the following type / year/ application

D0AZ-17271-A = BLUE, 16 tooth (type 3, C4 auto 1970 351 / C4 2.75 Axle ratio w/G78-14 tire ---- Also Police, taxi or rental with 3.25 rear axle ratio!

C7SZ-17271-A = GREEN, 17 tooth (type 3, C4, C6, FMX 1970 351 w/ 2.75 axle ratio and F70-14 tire

C7SZ-17271-B=GRAY, 18 tooth (type 3, C6, 1970 460 w/ 2.80 axle ratio and 9.15X15 tire

C7VY-17271-A=TAN, 19 tooth (my factory FMX, 3.00:1 gears) (type 3, 1970 C4, C6, FMX 302, 351, 429 w/ 3.00 axle and F70-14 tires

C8SZ-17271-B=ORANGE, 20 tooth (type 3, C4,C6, FMX 302, 351,429 w/ F70-14 and 3.25 tire

D0OZ-17271-B=PURPLE, 21 tooth (Not listed, please check your number?

There you go!
 

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I JUST PUT A 411 GEAR IN MY 9'' REAR IN MY 67 GT 390 WITH A C6 DO THEY HAVE A SPEEDO GEAR THAT IS CLOSE TO A 411 OR DID THEY MAKE ONE AND IF SO CAN YOU TELL ME WHAT COLOR AND TOOTH I NEED .THANKS CATMANDO
 
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