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I took the car out today for the first time in 2 months (we've had a lot of rain) and discovered that while the speedo works fine (hence no problem with the cable), the odometer is not turning over. Any ideas on how to diagnose the problem further?
Thanks,
Jake Powel

Nothing you can do without taking the speedo out of the dash cluster and open it up to find the problem.

The cable drives the main input shaft of the speedometer. That shaft contains a worm gear for the odometer drive and terminates at the magnet which induces the eddy current in the cup for the speed portion. As you surmise, since that portion is working, the problem is most likely in the secondary drive to the odometer.

The worm portion drives a spur gear on another shaft and depending on the complexity, can have one or two more shafts with gears to change direction and revolutions before it reaches the number reels. I don't know if 37 had the trip odometer. If it does, you may be lucky and find that reset movement has stuck and disconnected one of the shafts at a drive point.

Another possibility is speedo was jarred and one of the shafts or bearing points was moved enough a shaft fell out of position and the thin spur gears have lost mesh.

More likely the lube has completely dried freezing a shaft at some point. When that happens the usual result is one of the shafts is twisted or damaged or a gear is stripped.

If you find either condition, then a new speedo or repair at one of the instrument shops is the option.

Thanks Howard. I had pretty much resigned myself to some minor surgery on this item, but if you are right about the stripped or bent gear do you have any recommendations for repair sources?

Jake

There are quite a few speedometer repair facilities that advertise in Hemmings. HH%6 may have a particular choice, I've used both Reynolds (in FL) and John Wolf for various instruments - I'd call Wolf first as I've used him more recently. Class work, good pricing.

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Many thanks!

OK I finally bit the bullet and removed the speedometer. For the information of others who may not have done this on a 1937 115C, the process involves removing the panel holding the speedometer and is quite simple. First, detach speedo cable at back of unit, and 3 lights clamped to the unit. No longer trusting my memory, I labeled the lighting wires first. If your car has a defroster, it is helpful to remove the defroster tubing from the windshield mounted outlet. The panel itself is secured by six machine screws, all with 5/16" nuts. Two screws are welded to the back of the panel at the top and the others go through the small plates holding the bottom of the panel to the instrument frame. I was expecting to need WD-40 but it turned out all the nuts turned fine. I am attaching photos of both the instrument frame with panel removed and the backside of the panel showing with the speedometer still mounted. Tomorrow I will start contacting repair resources. Thanks everyone for your interest and info.

having trouble getting the pictures to show up

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back of panel

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Afterword on this issue. I did get in touch with John Wolf who repaired both the odometer and the clock in good time. On the clock, he repaired both the original movement, which I have stored, and installed a new quartz movement. I reinstalled the odo and clock by November last year and they continue to work fine about a year out. Thanks again for commenters steering me in Wolf's direction.