Topic: Speedo Cable & gear, tire size question

[Angela]

For a '67 390 C6, originally shipped with F70-14 tires I believe I should have:
(a) C7ZZ-17260-C speedo cable
(b) C1DD-17271-A speedo drive gear
(c) BLACK, 20-tooth driven gear

First of all, in yellow ink I find "C7ZF-17260-C FOMOCO" on my speedo cable. I don't know why it says C7Z'F' instead of C7Z'Z'...perhaps someone can educate me? I thought the "F" stood for "general parts or something like that and "Z" is for service parts? Do I have the correct cable?

The driven gear on my speedo cable looks yellow-white (not black per above) and has 19 teeth (not 20 per above)

Questions:
(1) All else being equal, if the number of teeth on the driven gear decreases, the indicated speed in MPH increases or decreases? I suspect the answer is the speedo will indicate a slightly greater speed than actually travelling, as the number of driven teeth are reduced. I'm not certain that's correct.
(2) Obviously, I'm not running a set of NOS F70-14's, rather a set of tires which match the diameter of the F70-14's as closely as I could find:
F70-14 diameter = 26.24"
My Tire diameter = 25.60"
So all else being equal, the slightly smaller dia tires I'm going to use should in theory render a slightly faster speed, right? Example, if the F70-14's indicated 60 MPH, to stay at 60MPH with my smaller dia tires the speedo would read something faster than 60 mph?
(3) Ultimately, I'm trying to figure out if I need a driven gear with fewer or greater # teeth than original, given my tires are slightly smaller in dia than original. I think I need a gear with more teeth than the originally specified 20 or 19 that I count of the cable. I suspect I want 21 (if that's even available). 

[jwc66k]

You need the rear axle ratio to determine the number of teeth. There is a chart in the 1967 Mustang Chassis Assembly that details all the tire size, axle ratio, transmission and gears including teeth.
There should be no assembly line part for your car marked C7ZZ. That spot in the number, the second "Z", indicates who has design/procurement responsibility. After all the engineering/procurement/assembly is done, the item becomes the responsibility of the service group which, for Ford cars, is identified as "Z". Lincoln and Mercury have different service ID letters. Back in the service days, when a dealership needed a C7ZZ-17260-C speedometer cable, that was the number he used. If they were out, it was ordered from a district service warehouse. When the warehouse got the order, that's the number they had on the shelf. If the warehouse needed more, they ordered that same part from a list of preferred manufacturers who used an original Ford engineering drawing that said to build the item a certain way and mark it C7ZF-12760-C, but to mark the box with the service part number. You need to spent a lot of time in production planning, logistics, scheduling and manufacturing to comprehend that part numbers are a pain in the -
Jim

[Angela]

Hmmm, interesting explaination concerning the 'F' in C7ZF; thanks!

Rear axle ration = 3.25, and if I read the table correctly gives me the 20 teeth driven gear as stock. I'm wondering, however, if I should use a 21 tooth gear to compensate for the fact that my tire dia is slightly smaller than the stock F70-14s.

[jwc66k]

Oops, sorry, the "F" indicates the carburetor, distributor, and others engineering design group.
Jim
(From my own observations, there was "poor" communications between groups, lot's of friction and internal politics back in them good old days.)

[Angela]

I'm attaching a picture indicating the C7ZF part number... this clearly isn't a carb or fuel-related part, thus I'd still like to better understand the 'F'. 

[jwc66k]

The part is/was under the design control of the group that designed the carburetors and distributors, identified as "F". That is all.
Jim

[TLea]

I'm attaching a picture indicating the C7ZF part number... this clearly isn't a carb or fuel-related part, thus I'd still like to better understand the 'F'. 

F is not a part # it is and engineering number. The Z indicates service parts.

[jwc66k]

F is not a part # it is and engineering number. The Z indicates service parts.

The "F" in the fourth position of this type of part number indicated the design control of the part - period. When it became a service part, a "Z" was used, indicating service control. The part is still marked with the "F".
Jim

[J_Speegle]

Also don't mix up part numbers (number on the tag or box) and engineering numbers (number on the part)   

[TLea]

The "F" in the fourth position of this type of part number indicated the design control of the part - period. When it became a service part, a "Z" was used, indicating service control. The part is still marked with the "F".
Jim

I think you are missing the way ford did parts. When a part was made for assembly line it didnt need to be identifieded by a part # They wouldnt change the building (usually) of a stamp on a part to identify when it went  to service. In the case of speedo cables they went in a bag and got the Z on the outside to indicate replacement parts as I previously noted.
Speedo cables on assembly line ususlly had a color ID label

[jwc66k]

I think you are missing the way ford did parts. When a part was made for assembly line it didnt need to be identifieded by a part # They wouldnt change the building (usually) of a stamp on a part to identify when it went  to service. In the case of speedo cables they went in a bag and got the Z on the outside to indicate replacement parts as I previously noted.
Speedo cables on assembly line ususlly had a color ID label

So by your method, a part was identified by a "color" dab by on its original drawing, purchased by "color" dab, made by "color" dab, received by "color" dab, inventoried by "color" dab, kitted by "color" dab, all before it was assembled.  think not. Yes there were quick way used to identify parts on the assembly line, paint for one, a tag with a rotation number, etc, but the entire process up to the assembly line where the "color" was applied, was by part number. 
For service, "color" was not used as an part ID, a part number was.
Jim 

[TLea]

So by your method, a part was identified by a "color" dab by on its original drawing, purchased by "color" dab, made by "color" dab, received by "color" dab, inventoried by "color" dab, kitted by "color" dab, all before it was assembled.  think not. Yes there were quick way used to identify parts on the assembly line, paint for one, a tag with a rotation number, etc, but the entire process up to the assembly line where the "color" was applied, was by part number. 
For service, "color" was not used as an part ID, a part number was.
Jim

You missed it, again. I am not talking about service parts. Engineering numbers and part #'s are not the same. You filled in gaps I never stated. I never said it wasnt designed, built ordered etc by a color daub. It was designed, built ordered etc by engineering #
The discussion here is about the differences between engineering numbers and part numbers and all that was offered was the differences between the two.
Please dont make me type all this again, its exhausting

[jwc66k]

You missed it, again. I am not talking about service parts. Engineering numbers and part #'s are not the same. You filled in gaps I never stated. I never said it wasnt designed, built ordered etc by a color daub. It was designed, built ordered etc by engineering #
The discussion here is about the differences between engineering numbers and part numbers and all that was offered was the differences between the two.
Please dont make me type all this again, its exhausting

Nope, you missed it completely, and you are making it harder for anybody to understand. An engineering number is a part number, please leave the pound sign out. Sometime in the manufacturing cycle, that engineering number evolved into a service part number. I got too many years in design, engineering, procurement, logistics and manufacturing  educating people in what a part number is and represents.
Jim

[J_Speegle]

Nope, you missed it completely, and you are making it harder for anybody to understand. An engineering number is a part number, ......

Uhhh??? I can grab or look up (in the MPC) a number of examples -

- one number on the box or tag and

- another number (not the same one as above) cast, printed or stamped in the part.

This can and does often confuse many when searching for parts armed only with a part number


NOTE - We are getting way off of the original topic

[TLea]

Nope, you missed it completely, and you are making it harder for anybody to understand. An engineering number is a part number, please leave the pound sign out. Sometime in the manufacturing cycle, that engineering number evolved into a service part number. I got too many years in design, engineering, procurement, logistics and manufacturing  educating people in what a part number is and represents.
Jim

Well Jim I guess you are just smarter than me so you can just keep on educating all of us. Good luck with your understanding. Why don't you go into Ford and order a part under C7ZF and let me know how it works for you.
I give up.