How do I know if my car has original parts?

I am having a hard time finding the plastic gear with 20 teeth for my speedometer cable. I purchased one with 20 teeth like mine from SO-Cal. They say thats the one but the one I pulled from my car looks different. They both have 20 teeth. Does it matter if the automatic is C4 or C6? How do i know if my car came with the C4. Did mustangs in 72 Iven come with C4? A mechanic told me that all mustangs between 71-73 came with a C6 only.

they came with C4,C6,and fmx automatics

It looks different how?

My gear sits about 1/4 inch taller and the teeth itself are longer then the new one that socal sold me.

Your VIN or door tag should tell you what trans your car came with.

Here is a link to the VIN decoder. http://www.7173mustangs.com/misc.php?page=1972

He gears for the automatics fit all 3 transmissions. The top loader gears are in reverse direction. Wouldnt go in the trans. But if the one you have is longer it might not be the right one. You can get correct gears from almost any mustang supply house because they go in the 1970 and earlier cars also.

If that is not the correct gear, then I'm sure Don or one of the other vendors on this site can get you the correct one.

there is a picture on my site

Try and compair them - might be hard from a picture though

Item #C0DZ-17271-20

SPEEDOMETER GEAR 20 TEETH

Automatic and 3 speed.