I have a 1975 ford f-350 2wd 4-speed 390. it didn't have a speedometer cable, so i don't know what kind of gear i need, i bought the cable but not the gear because there were 4 or 5 chooses, is there a site or some way i can find out what size i need?

 

Have you checked with a Ford dealer?

 

Was the cable casing there ?
I believe the gear choices are different colors which usually designate the number of teeth. If you are able to remove the driven gear from the back of the trans it will be one of those colors and if it looks OK both at the gear teeth and the end that the cable goes in, It should work alright. What you can try is insert the cable into the casing from the speedometer end connect it to the speedo head and rotate the cable. You may need to rotate it in both directions to see if it works. If the needle on the speedometer moves it should jump up to 5-10 mph that would tell you that everything from the trans end of the cable to the dash is OK. Connect it to the trans end and test drive it.

 

there was no gear or cable so I'm SOL-ed on knowing what kind of gear it had, but i'm not sure if there is a way to count the teeth with in the trans or a code i can search or something...

 

What was in the place where the holder for the driven gear goes into the trans?

There is a spiral gear on the output shaft in the trans that indexes with the gear you are seeking.
Try a couple of trans shops , they probably have a pile of old stuff and they may have what you are looking for. They used cable operated speedometers for many years and they could possibly come up with the parts you need from something newer than 75.

 

the drive gear hole had a red cab you get plastic hose then a little peace of tin bolted over the top. no gear no nothing.

 

Your best bet is either a salvage yard or a trans shop. Right now the gear is only part of the problem, you're going to need the part that the gear goes in that goes into the trans. You may need to try several trans shops.

If I remember correctly they used mechanical speedometers into the late 80s and early 90s. See what a Ford dealer has for the later years one of the choices just may work.