how can i tell

[67 F100 in Richmond]

what kind/size/tooth count gear i should have for my speedometer i think when the PO changed the transmission to a 4 speed they put back in the orignal. The numbers on the transmission is that my key to finding the right gear?
i have checked the speedo and it works when i hook the cable up to a drill and make it spin. (i replaced the cable)

[fordman]

the number of teeth is determined by the size of the tires and the size of the rear end ratio. there is a calculation that needs to be made in order to know the correct number of teeth.

[67 F100 in Richmond]

so if someone changed out the transmission would that make it not work or am i completely off here?

[fordman]

it should work if everything is there or not broken. maybe the gear is broken if it isnt working. you would have to take it out of the trans to inspect it.

[67 F100 in Richmond]

all the teeth are there and it slips in with no issues...

i have taken the instrument cluster out and driven with the speedo cable so i could see the end and it does not spin when i am going down the road...

that is what lead me to believe the gear was the wrong one... ?






a thought...
is there another gear that the speedo gear connects to inside the trans..
of course there dummy but what if that was missing...

sorry talking to myself as i type..

i will crawl under this weekend and see what i can see...

[70shortwide]

sounds like a broken cable to me...

[67 F100 in Richmond]

sounds like a broken cable to me...

Brand new replaced that first...

had same issue on 65 mustang and was broken cable..

[70shortwide]

oops... musta skipped right past that

[fordman]

if you can spin the cable from the tranmission end and the speedo works then all of that must be good. it has to have somethin gto do with the holder od the gear. unless the gear inside the transmission on the rear shaft is broken or missing. one thing i would look at is the plastic gear holder. is it rounded out? the speedo cable is square. so should the holder be square. then loo to see if the plastic gear will spin the cable when its out of the transmission. if it does then it is a internal gear problem. take a flashlight and see if you can see the internal gear and if looks bad or missing.

[FORDification]

Yes, there is a drive gear on the output shaft (inside of the transmission tailhousing), and a driven gear on the end of the speedometer cable...and the two are supposed to mesh together. Either (or both) could be damaged, but I think usually the drive gear is steel, so it's probably not that. Since you said you've disconnected the cable from the instrument panel and can see that the cable isn't turning, then you need to follow fordman's advice by disconnecting the cable from the transmission and spinning the inner cable with your fingers and see if the speedometer moves. If it does, then the cable is fine and you need to turn your attention to the plastic gear on the end of the cable and the one inside the transmission that drives it.

[cdherman]

The spiral "drive" gear inside a t-18 tranny is plastic. I know -- I replaced mine when it was doing the same thing as is being described here.

You can stick your finger in the hole and feel the spiral gear. If its sort of "cupped" or dish shaped, then its shot.

Replacing the spiral drive gear on a t-18 requires removal of the tail housing, several split rings as well. But it can be done under the truck.

Finding the correct spiral gear (7 tooth or petal is standard for a truck I think) is more of a challenge. I got mine from Inland Truck here in Kansas City, but they had to special order it from Rapid City. I was unable to get one from any other place, including Ford as well as online places, LMC etc etc etc.......