Speedometer core broken 62 Hawk

[Waltb]

The core wasn't spinning (while driving down the road) so I pulled it out. About 63" long. The tranny end isn't squared off, like the speedo end, so I figure it has snapped. Why did it snap? It turned freely in the sheath, by hand, well lubed. I haven't checked the speedo in the dash, I don't know how to determine if it is ok. If I buy a new core, will I have much problem getting out the broken section still in the sheath? I haven't been under the car yet, it is new to me. What lube do I use when replacing the core? Thanks, guys.

Walt B

[John Kirchhoff]

Usually a speedometer cable is broken when there's a dry spot or rusted area and causes the cable to bind up. I've found that on those, the end of the cable will be twisted down to a point at the end of the break. If the cable is kinked or has too sharp of a curve, often times the speedo needle will waver back and forth. They also usually waver right before the cable breaks as the cable winds up and then releases. I've carefully used a torch and brazed the cable together with success. If the cable is well lubricated the entire length, it is possible that the bushings in the speedo are shot. However, it's usually easy to tell if they're very badly worn since periodically the needle will peg itself on the high side at supersonic speed. This is because the worn bushing let metal touch metal instead of letting magnetism do the job. To check the speedo, on the back side where the cable threads on is a little brass projection that the square end of the cable slides into. You should be able to reach behind the dash and spin it with your thumb and forefinger in the same direction the needle travels. The needle should move as it's supposed to. A good spin will probably get it up to say 20 mph but if you're in close quarters and don't have much room to work, a little spin may only get it up to 5-10 mph. Either way, as long as the needle goes up and then back down to zero, it's probably fine. Should the needle stick, not return to zero by itself, you can make it return to zero by rotating the shaft backwards and the needle moves in synch when you rotating the shaft which seems to turn roughly or drags, it's most likely worn bushings. If the needle doesn't return to zero, but the shaft rotates smoothly, it's probably the spring.

As far as getting the remainder of the cable out, if you disconnect it at the tranny, the end should either be easily accessable with needle nose pliers or it may even stick in the tranny as you with draw the outer sheath. Sometimes if the cable route has a depression before it gets to the tranny, any oil added to the upper end will collect in the low spot but never made it to the uphill section between there and the tranny. I usually use motor oil for lube. I know they make graphite based lubes for cables but my experience has been that eventually it ends up turning into a solidified glob somewhere which blocks the flow of oil if you ever try to use oil later. I wouldn't use grease because in cold climates, it would get very stiff and possibably twist the cable.

[Waltb]

Thanks, John. That gives me a lot to work with. I'll check things out tomorrow, before buying parts.
The break in the cable end is clean, almost like it was cut. The cable appears to be well lubed the entire length. The speedo has not worked since I bought it a few months ago, so I don't know about how the needle vibrated when it did operate. I just tried to spin the speedo shaft, and although a little resistant at first, it spins freely and the needle moved to 10 mph and dropped back properly. So it appears that the head is ok, just the cable needs replacing. I presume that the pinon gear is ok. No way to easily check that, I suppose, but then there is no reason to suspect a problem there. I still don't know why the cable core broke, however. I just inspected it again, and can't see any rust, but then, as I drew the core out, any lube would have covered any bare metal that may have rusted.

Thanks for the help.

Walt B

[37CoupeE]

Years ago I learned a trick from a motorcycle mechanic.
He used to lube all cables on a motorcycle with transmission fluid.
The reason is that it lubricates well and does not stiffen up the way motor oil does.
I have used this for lubing speedo cables with no adverse problems.