Speedo cable with Columbia overdrive
 

Hey Fellas,

I have bumped up against an issue on my 1941 mercury convertible. The speedometer cable recently broke, it was the end at the transmission that snapped off. I ordered a new cable and it worked about 10 miles before it broke again. The issue appears to be that cables are too long which is keeping it from being in a relatively straight line so as the car moves the actual cable is trying to spin instead of just the inner part spinning, the cable has to have some loops in it to get to the transmission because of the 71 inch length.

The set up is a cable is coming out of the dash and into what I will call it a speedo junction box. Then the cable runs out the bottom of that and down to transmission. I'm not certain what that speedometer junction box that is mounted to the fire wall does but it seems I need a cable designed for that box VS a "standard" one. Hoping someone has experience with this. I have attached a picture of the piece mounted to the firewall.

Re: Speedo cable with Columbia overdrive
 

The way that cable is looped beneath the car is exactly what Columbia CO. advised / illustrated.
I have shortened the cable to eliminate that loop simply for a better appearance.
Breaking in ten miles suggest there is something else binding. Perhaps the drive gear?

If you are unable to shorten that cable and remain confident that is the issue, you buy a kit (amazon, ebay, etc.) and make the cable and length you like. The kits are cheap and easy to use.
To shorten the housing, twist off one end (I usually do the lower end), cut the housing and twist the end back on.

Re: Speedo cable with Columbia overdrive
 

Kube,
Thanks for the info. I am hearing a small noise coming from what I thought was the speedometer in the car, almost like I can hear the cable turning? I have some additional questions. Do you have a diagram or drawing that shows the direction that Columbia advises the cable to go? Also are you able to link the inner cable you use to customise the length from Amazon or wherever. Lastly, when you say drive gear, what are you referring to?
Thanks in advance.

Re: Speedo cable with Columbia overdrive
 

my research tells me that that box alters the ratio of the cable only when the OD is activated. if so, t wouldn't surprise me, as already suggested, that a custom cable may be necessary... or maybe a similar cable from an earlier ford or mercury could be used? you never know.

and do we even know if the OD is working or the "ratio box" for that matter? if that's the case, why not bypass the box altogether? for it's possible that the now broken would have worked well in a car without a working OD.

and another thought...do we know that it, the "ratio box", wasn't the root cause of the breakage in the first place?

anyway, if i was in this situation, i might simply verify that the broken cable was the right length and that both ends of it fit properly, install a new one and call it a day. :)

Re: Speedo cable with Columbia overdrive
 

Huey is correct in that your "junction box" is required to change the ratio when the OD is engaged. There are several reasons for your malfunction, one of which you've mentioned, incorrect length of cable. The cable sheath and its internal cable must match correctly, or either the cable won't reach far enough, or for your problem, may be even as little as an 1/8" of an inch too long. Extra loops in the sheath are not an issue as long as there are no tight loops or kinks. Another cause, likely the problem you have, is the lubricant has dried up in the speedo or in the ratio box, which will bind the cable and cause it to kink and break.
Having never dealt with a setup having an OD, i'm out on a limb here, but it's logical that you have two separate cables in sheaths, one from the tranny to the ratio box, and one from that box to the speedo? Those cables also require lubrication, so you do have your work cut out for you unless you can find an old fashioned speedo shop in your town.

Re: Speedo cable with Columbia overdrive
 

Re: Speedo cable with Columbia overdrive
 

1stford,
I have attached a scan of the 1940 Ford Columbia instructions. Although 1940 Ford, it is very similar to your '41 Merc installation.
Note also the speedometer changer is always engaged whether in OD or not. Think of it as a small transmission. There are gears in there :)
While I suppose it's possible the issue stems from that changer, it is highly unlikely. The gears are fiber and when on rare occasion they jamb up, the tiny teeth sheer.
I might suggest you remove both speedometer cable assemblies, remove the cable from each, wipe it down with mineral spirits, coat with a very light oil and reassemble.
then you can be reasonably sure the cables are not the issue.
You can, if you like, bypass the changer temporarily and route the lower cable assembly directly to your speedometer. If it works well at that time, the issue rests in the changer and / or the upper cable.

The speedometer drive gear is what many call the "turtle". It is the piece on the torque tube that the lower cable assembly attaches to.
That drive gear assembly can get gummed up. Easy enough to remove it, clean it out very well and reinstall. That gear within the housing should turn freely with your fingertip.

Re: Speedo cable with Columbia overdrive
 

In addition, when you clean the cable also clean the inside of the housings with the inner cable removed. Many times grease has been used on the inner and is gummed up now inside the housing.

The "speedo junction box" is actually a Stewart Warner speedometer transmission. When you shift into overdrive the speedo transmission is also shifted, increasing the ratio so the speedometer reads correctly. I disassembled mine and found lots of congealed old grease. The casings pull apart and have a thin gasket between the halves. John Connelly sells these gaskets. [email protected], or (951) 719-4077
You could also use Permatex blue form-a-gasket instead.

https://www.fordbarn.com/forum/attac...4&d=1765978575

https://www.fordbarn.com/forum/attac...5&d=1765978575

https://www.fordbarn.com/forum/attac...6&d=1765978575

https://www.fordbarn.com/forum/attac...7&d=1765978575

https://www.fordbarn.com/forum/attac...8&d=1765978575

https://www.fordbarn.com/forum/attac...9&d=1765978575

Re: Speedo cable with Columbia overdrive
 

All good suggestions. I would take everything apart, clean and lube. When my Harley panhead speedo quit. I thought it was lack of lubrication to the cable. John Bordas in Texas, the guy I sent it to for repair, like ford38v8 mentioned, said it could have been the lube in the speedometer itself that has dried up causing it to lock up and twist the cable. He also mentioned make sure the cable is not too long or short, this will damage the speedometer. An 1/8"and no more then a 1/4" long past the end. Running the speedometer off a drill may or may not prove proper lubrication, since the drill will not lock up like a speedometer cable.

Re: Speedo cable with Columbia overdrive
 

Good points.

Re: Speedo cable with Columbia overdrive
 

I find it amusing that Columbia had to provide a little overdrive unit for the speedo cable.

Re: Speedo cable with Columbia overdrive
 

There were better ways to do it if it had been incorporated into the design, but remember, the Ford was a finished product, the Columbia an aftermarket accessory.

Re: Speedo cable with Columbia overdrive
 

Not possible when everything was mechanical and the reason we like our old cars :-)
Electronically controlled speedometer adapter perhaps ...

Re: Speedo cable with Columbia overdrive
 

The turtle could have been located at the final drive.

Re: Speedo cable with Columbia overdrive
 

But then the speedometer would indicate a slower speedometer speed with the OD engaged.

The only way I can see to do it would bee to have a special axle with a gear on it to drive the turtle.

Re: Speedo cable with Columbia overdrive
 

And for a gear on the axle, the speedometer would fluctuate going around corners due to the differential.

Re: Speedo cable with Columbia overdrive
 

I said final drive, you said axle. I think we’re on the same page with that, right?
And about fluctuation going around turns? I think I’d rather have a tach than a speedo if I was going to race in a roundy round! 😎

Re: Speedo cable with Columbia overdrive
 

Late 30’s Lincoln Columbia had the turtle mounted on the axle housing.

Re: Speedo cable with Columbia overdrive
 

Considering most people, (myself included) will not preform regular maintenance on a speedometer until there's a problem, the lube dries up. At this point, if it were mine I would send it out and have it checked.

Re: Speedo cable with Columbia overdrive
 

i'm pretty sure the "speedometer ratio box" is activated by manifold pressure.

IOW it's the RPM of the engine, possibly in concert with the overdrive switch, that activates the box and so changes the speed of the cable attached to the gauge itself.