Speedometer issue

[elorenzof]

Driving to work this morning Phyliss' speedometer went crazy and making noise and saying i was going 100mph. Is it the speedo cable or the actual speedometer? the mileage counter works correct. 1970 c10 350 2wd long bed orange and white automatic

[dmjlambert]

I think probably the speedometer cable. I hope you mean bouncing to as high as 100, and not staying at 100, otherwise slow down...
I suggest have a look at the cable inside the cab, and in the engine compartment, and under the truck, to make sure it did not get hit by something such as road debris, and damaged or kinked. If it look OK from the outside, inspect the inner cable and lube it and see if the problem persists.
http://67-72chevytrucks.com/vboard/s...d.php?t=793443

[lutronjim]

It maybe the unit. If the bushings wear enough for the magnetic cup to touch, it will peg or greatly increase the speedo.

To test cable you can unscrew the casing from the speedo and pull the cable all the way out. It wont come out from the tranny end. The speedo end has a washer to keep it from being pulled. You can replace the cable by just pushing back into casing and rotating until the squared tranny end goes in.

Hold the ends in your left and right hands between your thumb and index finger and 'roll' it clockwise and back. If the cable has problems you can feel it 'bump' as you twist.

I would suggest lubricating with graphite if needed. Grease and thick oils can cause trouble in winter.

[HO455]

I would also say it is the unit. Mine will go haywire if I go above 80 mph. After coming back down it wants to drift up or down and it makes noise. So far it goes back to normal after being at zero. Knock on wood.
Lutronjim has some good advice on checking the cable out before going further.
Drop a PM to Tbone1964 he is the local expert.

[Sheepdip]

Mine was bouncing around, lubed it at the odometer end with plenty of graphite and it went away. I had the dash out to install one of TBONES Volt Meters in place of the Ammeter so it was easy to do.

[LockDoc]

-
Unscrew the cable housing from the back of the speedometer. Pull the cable out and inspect it for any kind of damage. If you find the cable is frayed or kinked replace it. If not, wipe it down with thinner or solvent of some kind and lube it with some 3-in-1 oil or gun oil, spray some penetrating oil with Teflon in it down inside the housing and insert the cable back into the housing. Screw the housing back into the speedometer and test drive it.

I would not recommend raw graphite because it turns into a gummy mess if it gets wet or draws moisture. Regular speedo lube with graphite in it may be OK because it is a solvent based graphite and is thinner.

LockDoc

[Astro-Balls]

I took my cable all the way off of the truck, pulled the cable from the housing and flushed it out with solvent, you wouldn't believe the gunk that came out of it, cleaned the cable up after a soak in solvent and used Speedometer cable lube to put t back together, good as new..