Hey all, new to the forum and to the ford truck world so thank you in advance for all the help! I recently purchased a 1991 Ford F250 Custom with the 5.8L engine and manual transmission as a project/weekend truck and am loving it thus far. I have done a few things over the past month that I've had it:
~oil and filter change
~air filter
~plugs and wires
~new windshield wiper motor
~new/used wheels and tires
~new cat, the old one had fully rusted off
~I have replacement monroe shocks, just haven't had time yet to install
~new rear drum brakes

Rust wise, the ole girl isn't terrible other than the floor boards, which are good enough for use, but will down the line cut all that out and put in new pans when I acquire a welder.

I've been doing a lot of reading on here since I bought it and found may issues with the speedo/odo that other people were having, but could use some more input. Thus far the only real troubleshooting I have done on the issue is checked the fuse, which is good to go. Since both were not working I did not want to pull the cable out and start taking things apart without some more input, and I just haven't had the time.

So my question is, where do I start? Since they are both not working, would that mean its more of a cluster issue? Any and all input is welcome and thanks again in advance. I am not a mechanic, but haven't met too many projects that I can't work through. Thanks!

 

Disconnect the cable at the trans/t-case and spin it with your hand, if the speedo needle moves you know the cable and cluster are good. The bad news is that means the drive gear inside the trans/t-case is stripped and has to be replaced. If that test doesn't move the needle then it's the cable or the speedo, and so you know the speedo module itself can be changed without removing the whole cluster from the dash, just remove the dash trim and the speedo lense and trim and then the individual modules can be pulled out of the cluster.

 

and while you have the cable out of the trans, closely look at the gear. if the teeth look "cupped" in the center of the gear the gears are most likely worn out and need replacing. some times you can get lucky and get the speedometer working again by just replacing the cable gear.

 

Would the fact that they are both not working be connected or just by chance? What does the odometer use to function that might not be working?

 

both are run off the cable. if the cable does not spin, neither work.

 

Perfect, thanks so much for the help, hopefully next week I will have some good news to report. I know I can buy a new cable and a that I can buy a new gear for the cable if either of those are the issue, but what if the gears inside the tranny are worn. What steps would I take there to get that fixed or is it even worth it.

 

you would have to take the trans apart.
if i remember correctly you can get to it from the tail shaft, but it has been at least 30 years since i replaced one so don't remember.

 

OP says his truck has a 4 speed, but failed to mention which one it is.

Here's a pic of the Warner T-19, output shaft is 7061, speedometer DRIVE gear on the output shaft shown as 17285 (in pic at lower left).

But this is only the basic part number, so he'll have to look at his DRIVE gear to see how many teeth it has and its color.

 

i believe he would have the ZF-5 Bill.
unless of course someone swapped a T19 in place of the blown up 5 speed.

 

Um, none of that may matter. FIRST question is - is it 4x4 or 2WD?

 

Sorry for the lack of info, it is a 4x4 and a 5 speed manual, so I believe that would make it a ZF-5.

 

I'm going through the exact same thing.

My speedo gear looked worn, I replaced it, but speedo still isn't working. Looks like I'm going to have to get into the transfer case.

 

Transmission is irrelevant in this case; the speedometer cable comes out of the transfer case with a 4x4 truck.

 

Thanks again for all the info, I will start by pulling out the cable and hoping its either that or the plastic gear and go from there. Any idea what size and how many bolts hold that thing in there?

 

should be one bolt holding the clamp down. if i remember correctly you need a 1/2 inch wrench to remove it.