I'm working on my 1970 F250 Crew Cab, 2wd, 390 with a C6. My speedometer cable broke so I ordered a new one to replace it. I ordered the standard screw on speedo end and push in O-ring seal on the tranny end. Here is a link: Speedometer Cable and Housing | Dennis Carpenter Ford Restoration Parts . I've also had a leak at the point that the speedometer cable connects to the tail shaft. Upon removing the cable from the tail shaft I find my drive speedo drive gear assembly is different from anything I've ever seen. It has a screw connector on both ends. This is a C6, I even had it recently rebuilt. The shop said it had a "heavy duty tail shaft with bearings". I didn't think much of it until now. I called NPD and discussed it with them and they sent me the correct cable, it has a screw on connection on both ends.

Can anyone identify this tail shaft and speedo drive gear assembly? and how do I seal it, it leaks where the adaptor screws into the tail shaft.

Below is a pic of the speedo drive gear installed and the second pic is the cable adapter that screws into the tail shaft. This speedo drive gear shaft goes through the adapter. The speedo drive gear is steel.

 

Clean it then Put some thread sealer on the threads before installing it into the tranny. IF the cable coupler is leaking.
You might try this. I used a thin o-ring inside the threaded collar that butted up to the thread adapter boss face. Worked for my cable
orich

 

Thanks. So this isn't some unsual type of tail shaft/speedo drive? I've just never seen one that accepted a threaded cable coupler.

 

I don't know about the S/Drive but my model 24 trans case was some what like that.
Ford used 3 different types from what, I understand.
Some had the steel gears & plastic ones. Maybe differ then a car C6 tho:

orich

 

Thanks for the tip. I'll get under there this weekend and apply some thread sealant and install an O ring.

 

1968/72 F100/350 360/390 C6: Two different types of speedo cables. One type is 75.42" long, the other is 70.80" long.

There are also two different types of C6 speedometer DRIVEN gears (end of cable), one is nylon, the other is iron.

 

I still haven't tried thread sealant on the drive gear. Been busy so I just add a pint of fluid every other week. The weather is warming up so I'll get on this one soon.