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Old 03-23-2020, 07:46 AM   #1
rockfla
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Default Speedomter advice

I was working on fixing the speedo in the 39 Mercury this weekend so I pulled the front floor board and trans cover to access the speedo drive "Turtle" to install a new (good used) drive. I removed the old "turtle" and sure shootin' the drive gear in it was "convex" shaped worn right around the "middle" of the gear. SO I installed the new drive and (First question) I am assuming that IF it fits flush to the housing the drive gear of the turtle is lined up with the drive shaft???? Its fitting flush SO I connected the new speedo cable at the "turtle". Then I set about connecting the other end to the speedo which I did. Took the car for a quick little spin around the yard and NO speedo. SO I pulled back into the shop and double checked both ends to the cable....all looked good so back out of the shop down the drive to the street, NO spedo but when I got to the street and backed up to pull back in the speedo worked going back down the drive way getting almost to 20mph BUT this time when I pulled back into the shop it STAYED at 20mph. I put it in reverse and backed up and it fell back to "0", pulled back down the drive again and NO speedo, even after backing up again and pulling back into the shop. SO, I pulled the cable at the turtle and chucked my cordless drill to the cable and spun the cable to the speedo, it jumped up to 30mph.....good I thought SO I connected the cable back to the turtle and disconnected the cable at the speedo. I took the car backout on a drive and held the "speedo" end of the cable in my fingers and could feel the cable spinning in my fingers, connected it back and still NO speedo!!! ANY thoughts or suggestions???? Is there a sure fire way to make sure the turtle gear is meshing with the drive shaft?? Is it important to use some pliers to make sure that both cable ends are threaded tight on the turtle and speedo, not just as tight as I can get them b hand/fingers (I.E. could the cable ends not be engaging the drive sockets because the ends are not in far enough, I.E. not tight enough...are they that close in tolerances)???
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Old 03-23-2020, 08:15 AM   #2
Terry,OH
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Default Re: Speedomter advice

Finger tight is all that is needed. Did you lubricate the replacement turtle shaft and gear? what is the condition of the gear that is on the drive shaft under the turtle? Did you remove the inner speedometer cable and inspect it? It should be lubed with a graphite cable lube. Make sure the finger nut on the turtle is going all the way down to clamp the outer speedometer cable housing to the turtle face. From my experience you have to use an electric drill in the reverse mode to make the Ford speedometer read. If you install the turtle reverse the cable will turn in the reverse direction and you may get the speedo to operate. You could disconnect the speedo end and watch the inner cable to make sure it is turning. If the speedo sticks at 20mph it may be dirt or lack of use. Once you get it to read going fordward give it some time to exercise if it continues to stick the speedo will need some maintance.
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Old 03-23-2020, 08:29 AM   #3
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Default Re: Speedomter advice

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Finger tight is all that is needed. Did you lubricate the replacement turtle shaft and gear? what is the condition of the gear that is on the drive shaft under the turtle? Did you remove the inner speedometer cable and inspect it? It should be lubed with a graphite cable lube. Make sure the finger nut on the turtle is going all the way down to clamp the outer speedometer cable housing to the turtle face. From my experience you have to use an electric drill in the reverse mode to make the Ford speedometer read. If you install the turtle reverse the cable will turn in the reverse direction and you may get the speedo to operate. You could disconnect the speedo end and watch the inner cable to make sure it is turning. If the speedo sticks at 20mph it may be dirt or lack of use. Once you get it to read going fordward give it some time to exercise if it continues to stick the speedo will need some maintance.

First-Yes I lubed the turtle/drive shaft gear before I installed the turtle.
Second-the speedo cable is new
Third-I will look when I get home and make sure the housing is seated all the way on the housing of the cable.
Forth-YES you are right, drill in reverse to spin the cable in the "correct" direction.
Fifth- I did disconnect the cable at the speedo and pulled it out so I could hold it and drove the car, I DID feel the cable turning.
Sixth-I installed the turtle the same way the old one came off SO.....


Is there two different styles of turtles???? Gears cut on the "reverse" angle???
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Old 03-23-2020, 08:46 AM   #4
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Default Re: Speedomter advice

Here is the turtle and cable right now!!!
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Old 03-23-2020, 11:16 AM   #5
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Default Re: Speedomter advice

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I did disconnect the cable at the speedo and pulled it out so I could hold it and drove the car, I DID feel the cable turning.

Is there two different styles of turtles???? Gears cut on the "reverse" angle???

If you'll look, the turtle gear is essentially straight-cut. The spiral on the drive shaft gear is the one which determines direction.


It should be obvious that if you feel and see the cable turning, the turtle is doing it's job. Sorry I don't have the definitive answer for your problem. DD
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Old 03-23-2020, 12:14 PM   #6
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Default Re: Speedomter advice

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If you'll look, the turtle gear is essentially straight-cut. The spiral on the drive shaft gear is the one which determines direction.


It should be obvious that if you feel and see the cable turning, the turtle is doing it's job. Sorry I don't have the definitive answer for your problem. DD
that is my initial feeling, in that I felt it turning SO the issue has to be further up stream.....I'm leaning toward the speedometer itself BUT I wans't sure IF my paralysis of analysis was kicking in and be too focused to see the issue?? Thanks
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Old 03-23-2020, 05:23 PM   #7
Viv W
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Default Re: Speedomter advice

I had a similar problem with my model A and found that I had the wrong turtle on my car. Some of the turtle drives have a square to drive the cable, some of the early ones have a hole with a slot for the cable to drive. If you have the early type with the round hole and fit a square ended cable into it, it may drive enough for you to be able to feel it turning at the head end, but when connected to the speedo head the turtle will not have enough friction to drive the speedo.
Also check where the cable fits into the back of the speedo head. The cable should be squared off at this end and fit into a square hole on the speedo head, this hole or the cable may have been rounded out somehow.
If the above all checks out fine, then you need to remove the speedo head and carefully open it to check for stripped gears or lack of lubrication. Use vaseline jelly to lubricate the gears.
A word of caution when opening up and handling or stripping speedo's, the numbers on the mileage wheels are transfer printed and easily damaged by your fingers pressing on them, handle with great care,
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Old 03-24-2020, 07:32 AM   #8
rockfla
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Default Re: Speedomter advice

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Originally Posted by Viv W View Post
I had a similar problem with my model A and found that I had the wrong turtle on my car. Some of the turtle drives have a square to drive the cable, some of the early ones have a hole with a slot for the cable to drive. If you have the early type with the round hole and fit a square ended cable into it, it may drive enough for you to be able to feel it turning at the head end, but when connected to the speedo head the turtle will not have enough friction to drive the speedo.
Also check where the cable fits into the back of the speedo head. The cable should be squared off at this end and fit into a square hole on the speedo head, this hole or the cable may have been rounded out somehow.
If the above all checks out fine, then you need to remove the speedo head and carefully open it to check for stripped gears or lack of lubrication. Use vaseline jelly to lubricate the gears.
A word of caution when opening up and handling or stripping speedo's, the numbers on the mileage wheels are transfer printed and easily damaged by your fingers pressing on them, handle with great care,
Thanks, I'll do "closer" inspections of what you describe in the next couple of days!!!!
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Old 03-24-2020, 01:05 PM   #9
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Default Re: Speedomter advice

If the cable is turning, but the speedometer isn't work, or is erratic, it is very likely the speedometer is worn, allowing the magnetic disks to get out of alignment. The pot metal cases wear where the cable attaches. We send them to Bob's Speedometer in Michigan. They will give you an estimate of repairs and cost.. They also have a selection of rebuilt units. I bought a good one from them for my '47, giving my old one in trade. You can reach them at 1-800/592-9673. They have ben in business since 1929.
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