Hi All,

I have a 79 ford f150 ranger lariat 2wd with auto trans (C6). Since I got the truck, I have had speedo/odometer issues with the truck. The speedo worked but was way off by 10-15 mph fast. The odometer never worked. I normally had to do 75 to get to 60 mph.

I first wanted to correct the speedo issue. Tire size 235/75/R15 (so close to stock tires). After looking at my vin, it says I should have 2.75 ratio but I jacked one side up and spun the wheel and counted the revs of the driveshaft and turns out its a 3.5 ratio. I then checked the speedo gear and its an 18 tooth gear. So I imagine it should be close and not off that much. So I went ahead and bought a new cluster off of ebay, as I imagined the odometer was messed up, so must the speedo. Was cheaper than a new speedo so I went with that.

After painful dis-assembly with the cluster screws I finally got it out. I could not get 2 of the 4 screws undone. So I had to do the unthinkable. It came out without to much damage. Everything is still usable, but it won't matter because I got a new cluster anyway. Here comes the issues with the speedo/cable. I looked through many forums, watched many vids on this and I see it should come out quite easily. However after trying for hours, I could not get the cable loose no matter what I tried. I saw bucks vid and it came out nicely for him. Mine however was impossible. It actually looks like there is an adhesive on the cable end and I simply could not get it loose. So out the cable comes. It wasn't that long, and it had a square end like seen in a weedeater. Here comes my first question.

I see all replacements, and stock pictures of one single cable from speedo to trans. However after inspection in the engine bay, here is what I found. Two separate upper/lower cables. Does the 1980+ fords have this type of setup? My truck may be a late model year during production, so it makes me wonder if some of the 80s redesign features were incorporated into my 79:





If not, then it might be possible I have another frame/engine. I haven't checked everything as I don't have the time to drop the pan, check the crankshaft, and look for the vin on the frame to confirm. I do know my carb isn't stock either. its an autolight 2100, and not a motorcraft 2150. It makes me think I have some other motor as well, but again, haven't confirmed yet.

Moving on, I found another issue. Once I got the cluster out, I found these wires just dangling. One with what looks to be a turn signal cluster insert and another with what looks to be another one that should be there but isn't. (edit: The turn signal cluster is the ashtray light. Still not sure about the other) All my radio lights, vent lights, etc were working like they should along with the "lights" and "wiper" lights. THe only thing I could think of was again, the newer wire harness in the truck for the 80's models.



far left is the empty connector and on the right on top of the cluster connection is the dongle.


Now, moving back to the speedo in the taken out cluster, I wanted to investigate the issue as to why the odometer wasn't working. Turns out, it is due to fractures in the metal housing for the speedo. The brass/copper washer that holds in the worm gear was poped out, due to the fractures. No real fix it seems for that:



stress fractures in the metal housing that holds the brass/copper washer in place. You can see it sticking up here


There are fractures all throughout the housing from what I seen. Is this normal in these trucks?.

I realized at this point, I probably wasn't going to get that speedo cable off, but I tried anyway. Here is the end result. Good news is the worm gears for the odometer are still good, and it still functions good. So I can use those if my new one ever goes out.





Before anyone mentions anything about the speedo cable, I know about the plastic tab housing, and wiggling it back and forth. This one just wouldn't come out no matter what I did, and that is the end result. Has this happened to anyone else out there?

 

The reason you have a split cable is due to cruise control. That is the speed sensor there in the engine compartment. As for the wires, it is most likely for something you don't have, what I mean is an option. As far as the broken speedometer, I have never seen or heard of that, so I would say someone messed with it before, ie tried to "fix" it.

 

Thanks 4x4slik, good to know about the differences in speedo cables. I didn't realize that was the speed sensor for the CC. I found a cable on napa and i'll pick it up tomorrow.

As for the speedo cable, definitely. It looks like someone was in there before and messed around. Especially with the ashtray light. It was just dangling when I got in there. I don't smoke so didn't know it was out. Thanks for the help!

 

The speedo calculator says you need a 17 tooth gear to be accurate.

 

I've already looked and yes from the sound of that it should be 17. However, the speedo was reading fast, meaning I will need more teeth to reduce the speed. I am however going to replace the speedo itself first, and see the results.

I know these old speedos can become off once they get old, and will need to be recalibrated with a magnet. I have no idea how to do this. Its way before my time . I've attempted to find instructions on this but the best I have seen is people stating to put a magnet next to the speedo with a drill to run it in order to "realign" with the correct setting.

 

I'm having a really hard time trying to find the correct speedo cable. It seems the uppers with CC are VERY rare. The one at napa is for the 80+ models.

Will the upper speedo cable for the 80s models work just as good? I can't find a replacement anywhere for the 78-79. I think I found one, but that is 35 bucks plus shipping on ebay. Way to much for that.

I'm also not sure of the exact part number for the upper cable, otherwise I would be searching that way.

If anyone could help me out, I'd appreciate it.

 

I've bought them at Oreilly.