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Speedo cable in my '40 turned out to be snapped, about 3 inches from the transmission. As luck would have it, I got the correct Ford NOS cable off eBay the next day.
I started wondering about the 2-spd rear trucks. Not that I have any intention of shifting into 8.11, but was there some sort of converter on the 2spd rear trucks, or at these ratios, did FMC just figure 'screw it'?
I did see a pic of a unit that was electric, for '56... but my truck had a replacement late '30s Ford car speedo, and I (again) lucked out a few years ago & found an NOS big truck speedo. Either way I have no unit off the back of my speedo.
IF there's no such thing for circa 1940, would the speedo be set up for the higher ratio (5.83 in my case)?
Also, would there be any other cause of a snapped cable besides age & a lack of lube?
My speedo(meter) on my 47 2 ton with two speed rear had a complex looking affair with a sort of transmission looking mini gear box to accomodate the change in ratios. It didn't seem to work so I bypassed it and I think it's in a box somewhere on a high shelf. If you want it you can have it, but you have to come find it on your own...
I think in the thread I saw on the '56 (GMC) it was referred to as 'the turtle'.
In that I had to disconnect the driveshaft and move the parking brake assmebly rearward to even get to the trans end of the speedo cable, I can't imagine anything else down in that tight area- was this device on the back of the speedo? How is it 'activated' to 'change over' when the rear does?
GB is correct. On trucks with a vacuum 2 speed axle there is a device on the back of the speedo that "shifts" with the axle to provide accurate speed indications. There was a vacuum line running from the shift valve on the fire wall to the device on the speedo. I don't know how, or if, the trucks with the mechanical shift lever in the cab accomplished this speedo compensation.
Ya- mine is a manual shift rear. No signs I see that anything was mounted anywhere... except perhaps behind the original, long-gone speedo. I saw one person claim there was a manually-switched 'converter' for the manual Eatons.
As long as the speedo reads correctly for 5.83, I don't need a converter for 8.11.
There was a mechanical unit to shift the speedometer 'gear box' along with the axle in manual shift trucks. It was a cable affair. Mine had the same vacuum unit GB speaks of but i took it off rather than rebuilt the thing. You already know you're going slow when in low range, I figured I didn't really need to know _how_ slow
You can find the speedometer correction units on that auction site NOS. Search for "axle speedometer adapter" or similar. I see them for a large range of price. I picked one up a while back for $25 or so. I plan on using it running backward to correct for the overdrive gear in an auxiliary transmission.
If the speedo correction unit is removed/missing, is the trans geared to indicate the speedo correctly for the numerically lower ratio? IE; would it be correct for 5.83 and read wrong for 8.11?
It will be ~correct for 5.83 and very wrong for 8.11. Mine reads about 8-10% low without the correction unit, but I think it's because I'm running 8.25-20 tires.
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