Interior Spedo cable shears at diff

[Black Thumb]

I replaced my spedo cluster and ran a new line to the diff. The old one was sheared just outside the fitting. I went for a test spin, and got no reading. Checked everything again, and the new spedo cable was sheared in the same place.

I did not secure the cable at all. It was just loose, so the gentlest bends and no binds.
New cable arrives today, but I’d like to not repeat.

What, on earth, could cause this?

 

[CJ]

I am assuming that when you use the word diff you mean Transfer Case .
Can you clarify what you mean by shear? Are you talking about the internal flex cable, the outer sheath or both?
Which fitting? The one at the transfer case or the one at the speedometer?
A picture of the broken cable overall and at the fitting would help.

 

[Black Thumb]

Yes, the Transfer Case . Yes the internal cable. Sorry. Don’t know why a wrote the differential. It’s early and no coffee yet.

 

[CJ]

Which fitting? The one at the Transfer Case or the one at the speedometer?
A picture of the broken cable overall and at the fitting would help.

 

[Black Thumb]

By shear I mean snapped in half in an ugly, fraying of the cable manner. Just outside the fitting leaving about a half inch to grab. Old one was broken there and the new one was too.

 

[Black Thumb]

At the Transfer Case . Pulled the cap off, both to replace the old one and to check the new one, and both were sheared in the same place.

 

[CJ]

Good information. If you could please take close up pic of the two pieces so we can see where it twisted in two. About the only way that could happen is if the new speedometer is freezing up and stopping the cable from turning. I don't see how a nice smooth routing could cause this unless there was a manufacturing defect in the first cable.

 

[Black Thumb]

I did not “test” the new spedo. It came out of a box, but was old, so that could be it. Can I spin the new cable when it arrives to test? Is there normally enough slack in the inner cable to get your fingers around?

 

[Black Thumb]

I threw the short piece of cable away, about 1.5” long, so nothing to take pics of.

 

[CJ]

Because they are new old stock the lubricant could be gone. I would definitely relube the cable with some speedometer cable graphite. Just pull out the wire flex part and give it a light coat.
Yes you can spin it with a drill, but I would not do that until I relubed it.

 

[CJ]

Lubricant

Google Search

 

[Black Thumb]

Is speedometer cable graphite different than the graphite from the hardware store? I think I still have a bottle from Pine Wood Derby days...

Edit: sorry, didn't see the link. I've got all that stuff. Thanks! That is a very good thought, and probably right.

 

[CJ]

Just make sure you clean the wire cable and inside of the sheath of the factory oil lube as you can. The graphite lube and petroleum lube don't like each other. This is where brake clean comes in handy.

 

[Papoumd]

My speedo cable doesn’t go anywhere near the Transfer Case on my 72 CJ5 . I replaced it a couple years ago and it threads in to the side of the Transmission . How is it that yours runs to the transfer case?

 

[Black Thumb]

I'll try to take a pic. It sits back on the top of the Transfer Case and the threads come out of the drivers side.

On the vast majority of vehicles it’s on the Transmission for sure. Don’t know why they did it that way, except maybe so it’s easier to change the gear for different tires?

 

[CJ]

My speedo cable doesn’t go anywhere near the transfer case on my 72 CJ5. I replaced it a couple years ago and it threads in to the side of the transmission. How is it that yours runs to the transfer case?

View attachment 107009

@Papoumd , that is your Dana 20 Transfer Case . If it is near an output yoke for a drive shaft it is the transfer case. The Transmission does not have anything that has any drive shaft connection. The order of output is engine >> transmission >> transfer case. The reason the cable is connected to the transfer case is so that the speedometer is always accurate no matter if you are in low or high range. Your 72 has a Dana 20 transfer case. Here is a picture of the output of my 1972 AMC 304 v8 Dana 20 and I highlighted the speedometer cable connection.

 

[Papoumd]

Interesting. That is not where mine connects. I ran the cable myself and connected it directly to the back of my speedo gauge.

 

[CJ]

The picture you posted is the output housing for your rear driveshaft on your Dana 20 . Here is a picture of the output housing with the speedometer connection. This is not the Transmission but the Transfer Case .