Speedometer cable frozen

D

dajo

Junior Member
When speedometer cable stops turning (locks up) and does not break. Does it damage the drive at the transmission (turtle)? 1940 Fordor.
 
No. The cable is squared off at both ends, and slips into the drive on the turtle, and the driven on the speedo. When obstructed, the cable will twist up, shortening its length, pulling free of one end or the other, or breaking itself. The turtle, if it hasn't been modified, will survive anything the cable could do.
Suggestion: Pulling the cable out of the sheath is an easy task, but will soon get messy as hell. Before you start, cover your upholstery with tarps. Replacing it gets even more messy if done right with lubrication.
Exact length of the cable within the sheath is critical, and may vary from one vehicle to another. Starting with a cable as purchased, you may need to shorten it a bit so it doesn't jam tightly into the speedo, which can damage both, or cause erratic speedo operation.
 
Good to know thanks. I took entire cable out of car and removing the old drive cable was very difficult. Do you think this impending failure might have something to do with the speed being 15MPH off. Speedometer was steady and had very little needle movement with no indication of problem.
 
If the speedo was steady, no, the 15 mph off was unrelated to the cable unless, perhaps, the squared ends of the cable are rounded off to allow slippage? You'll need to determine the differential ratio, and tire diameter, then select the turtle ratio that will correct the mph problem.
 
I have 6.00 x16 Pie Crust Firestone tire, 3.78 rear gears verified by counting teeth on ring gear and stamped 9-34, turtle says 19 on it. Afraid there is no selecting gears to fix this. I was going out to check odometer accuracy when the cable decided to act up. Bobs quoted me $400-600 for speedometer work which I am trying everything to avoid.
Thanks
Dave
 
Check with Williamson's Instruments in Arkansas and get a quote. I used to use Baxter Ford in KS and they were very reasonable.Not sure if they still do them.
 
Since you have pulled the cable, you can easily check that the speedo isn't the problem. Either use a small blade screwdriver or square bit into the back of the speedo and rotate it. I bet it is not bound up. You can also buy just the cable wound wire, match it to your existing cable's length and trim it off.

https://www.napaonline.com/en/p/BK_6151797

Regarding the speedo being off, you didn't say whether it was high or low. A one tooth difference in the turtle to an 18, which will speed the reading up, or a 20 which will slow it down.


Chart is on page #640 of Green Book


551109
 
BTW, the turtle will take a one tooth change without modification. For two tooth difference, buy another turtle or grind to fit or by adding gaskets between the turtle and the torque tube..


Glenn
 
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I have a universal cable coming today. The speedometer reads 70mph at 55mph. Thanks to all of you with suggestions. Dave
 
Hi Dave,


I didn't mention that the gear in your turtle marked as 19 may not be. Easy to get it off and count the teeth.
 
Just checked speedometer and there is the problem, locked up. OK one minute locked up next. It was even running smooth. thanks Dave
 
Thanks again for the answers. I worked on the Waltham speedo lubed and calibrated. It was only showing 8 tenths when it should be a mile.. As soon as new cable comes in verification will be possible. Wasted $30 on universal to find out the crimp on end was not compatible with Waltham female thread connection.
 
dajo said:
Test drive results indicated 60 MPH actual according to Phone app 58MPH. I'll take that.
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Sounds like that small difference might be accounted for with a difference in tire pressure. Also, if I remember correctly something I heard many moons ago, the manufacturers lawyers require a slightly less than actual speed indication for liability reasons, which sounds lawyerish as all git out…
 
Does anybody else have a speedo that only works well at like 25+ mph? Mine bounces up and down below that speed. Tick. Tick. Tick. Sounds like a turn signal that is activated.
 
funoldcarguy said:
Does anybody else have a speedo that only works well at like 25+ mph? Mine bounces up and down below that speed. Tick. Tick. Tick. Sounds like a turn signal that is activated.
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Your issue sounds like a speedo cable lubrication issue. Disconnect from the speedo, pull the cable out of the sheath, clean with solvent, lubricate as you reinstall into the sheath. Before any of that, place protective tarps on your seat and floorboard, as this job can get messy. If after properly lubricating the cable the problem persist, then the Speedo itself will need cleaning and lubricating.
 
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