speedo gear

[Fordguy85]

how hard is it to change the speedo gear in the transmission ??

the speedometer doesnt work I have changed the speedometer its self, the speedo cable and still nothing, I have not worked on a T18 transmission before but have been working on old cars for roughly about 22 years , so how difficult is it ?

[chad67]

You didn't mention the condition of the driven gear for your speedometer. If it's OK, I would try to look at the drive gear by shining a flashlight into the speedometer hole in the tranny. Will the speedo work if you spin the driven gear with a drill?

[elsilerjr]

I had the same question, i just bought my first 67 f100, it has a NP435 trans and i pulled the cable out from the tranny and i can spin it just fine and it moves the speedo, so i assume its the gear in the tail shaft? is there anyway to test it? It didnt seem to hard to remove it, take drive line off, 4 bolts hold on the tail shaft and unbolt the support holding the tranny up?

[Fordguy85]

You didn't mention the condition of the driven gear for your speedometer. If it's OK, I would try to look at the drive gear by shining a flashlight into the speedometer hole in the tranny. Will the speedo work if you spin the driven gear with a drill?

the driven gear looked fine, when i pulled it out to change the cable it looked practically brand new. I can't get an angle to see in to tell if the drive gear is ok but thats the only thing it can be, unless i managed to replace the speedometer with another one that was broken, but doubtful, i can put a screwdriver in the end of it and it spins, can turn the driven gear on the cable and the other end of the cable spins so unless I'm missing something there drive gear is the only thing that can be the problem now

[mrtleavitt]

I changed the drive gear on my T19 last year not because it was worn out but because I have geared up my ring & pinion gears and I had the smallest toothed driven gear and my speedo was still off a few mph. It wasn't very hard at all. It would be a lot easier if you had it on a lift (i was on the garage floor). Your thought process is spot on as far as I can remember. The gear is held on by a key or keeper of some kind but basically the old one slides off and the new one back on. I think it is a snap ring...well more like a "c" clip. It took me a while to get that off, finally after I struggled with that clip for an hour I found that my Grandpa had a c clip spreader (almost like a snap ring plier) and I got it off in 5 seconds. You could do the complete job in a couple hours.

[Fordguy85]

anyone happen to know the which color is the stock drive gear color, i think the colors are yellow, white, and green ,

[mrtleavitt]

My stock one was yellow. I believe the one I put in was brown. Remember that your stock might be different from my stock.

[Fordguy85]

hmmm now Im lost, Checked the drive gear and the gear itself looked brand new, the driven gear looks brand new, I put a new speedometer in and a new speedometer cable in, and the speedometer is still not working, is it possible that the speedometer drive gear could be sitting free on the shaft and spinning on it instead of being attached and turning like it should ,

Im trying to avoid pulling the tails haft off because it looks like a pain in the butt and I Don't want to pull it apart unless i absolutely have to , any suggestions ??


I can stick my finger in the hole and feel the drive gear and its not moving freely under my finger so I'm not too sure what to do now , any possible way the gears aren't making contact with each other for some reason ?

[chad67]

Get an assistant and have them watch the speedometer while you spin the driven gear with a drill under the truck. If it works, pull the speedometer cable loose from your gauge and drive it and see if the cable spins. These tests should narrow it down for you.

[Fordguy85]

i have already done that, replaced a bad speedometer in the cluster, replaced the speedo cable cause it looked like it was on its last leg, from the dash to the transmission is all new

[mrtleavitt]

1. Jack up the rear so the tires are off the ground or to be a little more safe you can disconnect your drive line from the tranny.
2. Disconnect the speedo cable off of the speedo cluster.
3. Start up your truck and get the tranny moving so that your speedometer would start working (if it was actually connected).
4. Is the speedometer cable rotating while you are pretending to drive your truck?
5. If it is moving then the problem is in your speedometer cluster.
6. If the cable is NOT moving while you are driving then take out your speedo cable and the driven gear in the tranny.
7.. Then, have someone start the truck and get the tranny moving so that your speedometer would start working (if it was actually connected).
8. Then look into the tranny driven gear hole to see if the drive gear is working. (You will probably have to use a mirror since the hole is located high on the tranny)
9. If the drive gear seems to be working then the problem is your driven gear or the speedo cable.


This was you can go step by step and isolate the exact problem.

Remember - There are different styles of driven gears. Obviously there are different amounts of teeth that will compensate for different tire sizes and ring/pinion gear changes. But there are also left handed threads and right handed threads. Make sure you have the correct style of gear so that it is making contact with the gear on your tail shaft gear (drive gear).
See below for an example of the correct style of gear:

[Fordguy85]

did all that today, cable works just fine out of the truck , ran the truck and the gear in the tranny turns like it should, however when i put the cable in the hole the cable will not turn, so for some reason the two gears aren't making contact ? both the gears look to be in good shape so I haven't the slightest idea what the problem is , I'm fairly certain the color combo is correct, 19 tooth pink to a yellow , from what i have been seeing those are the two that go together , no clue here any advice ?

[chad67]

Is the inside of the driven gear where it drives the cable in good shape? It may just be turning free on the cable.

[Fordguy85]

it looks in good shape

[1967Rhonda]

did all that today, cable works just fine out of the truck , ran the truck and the gear in the tranny turns like it should, however when i put the cable in the hole the cable will not turn, so for some reason the two gears aren't making contact ? both the gears look to be in good shape so I haven't the slightest idea what the problem is , I'm fairly certain the color combo is correct, 19 tooth pink to a yellow , from what i have been seeing those are the two that go together , no clue here any advice ?

One question no one has asked.
Which Way is the cable core turning with the truck in a forward gear?
I had to order the driven(cable) gear with the threads going up and to the left because the previous new one(teeth up and to the right) had the centers of the teeth worn down like and apple core. This is a result of the driven gear teeth riding across the top of the drive(inside trans) gear teeth, perpendicular to the direction they should be. I assumed the driven gear was incorrect and ordered the (2nd) new one! Now, the gears mesh exactly as they should! BUT!!! When I disconnect the cluster from the cable and engage a forward gear, the cable turns counter-clockwise! With it connected to the speedo, there is no movement because the clutch that allows the cable to turn in reverse will not force the needle backward. So tomorrow, I will pull the tail shaft housing for the 4th time and hopefully find the correct gear somewhere local, and CHEAP!! Already $50 down and nothing to show for it other than a clean trans and the knowledge of the easiest way to pull that sucker out!!!