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September 2011 InBox - Letters To The Editor

Old Dinah
Rick Péwé
| Four Wheeler Network Content Director
Posted September 1, 2011

4xForward Plate Winner, Tire Contact Patch, and More!

4xForward Plate Offer Answer!
In the July 4xForward (“What’s the Diff?”) I showed a close-up of an old piece of machinery and asked for an ID based on that photo. The replies poured in. Of course, I did offer the incentive of a set of 4WOR plates to the first winning reader, but the amount of responses was still huge. Accordingly, we’ll send out more than one set of plates because there were some unique answers regarding the gears shown.

The photo showed the differential of a steam tractor named Old Dinah in Death Valley, abandoned in 1894. The differential allows the two giant steel wheels to move at different speeds, or differential gearing.

We were unexpectedly entertained by the amount of incorrect answers regarding this fine piece of machinery. While the spider gears and ring gear/carrier/bull gear are clearly visible in the photo, many people talked about planetary gearing (also known as epicyclic gearing) such as found in automatic transmissions, transfer cases, and other speed-style boxes. To be a three-member planetary gear system, it would have to have a sun gear and a planetary gear as well as an outer ring gear rotating in the same plane. The input/output speed and function are dependent on which of the three is held stationary or in combination with the others. The sun gear is in the center, with the outer planetary and ring moving or fixed around the stationary or moving sun gear. But a differential like Old Dinah’s is a simple early style that has the spider gears fixed in the outer ring gear, and they rotate 90 degrees from the ring gear rotation, which allows the spiders to differentiate between the two axleshafts, only one of which can be seen in the photo.

And yes, it is a tractor, it is steam powered, and it is a portal design, so kudos to all of you who included those answers. As for the right answer, a differential, notice the hint I gave in the title “What’s the Diff?”
—Rick Péwé

First Place Winner
I just received my July mag today, April 30, 2011. From the pic in 4xForward it looks to me like that is a bull gear differential, maybe in a steam engine tractor. Just to the right of the bull gear may be a large drive wheel. I’m probably way off, but that’s what it looks like to me.

Thanks for putting out a great magazine. I can’t even remember how many years I have been reading, but I enjoy every copy even if its full of Jeeps with Chevy engines (yuck) or vehicles I would never consider buying but which you are testing. I look forward to UA coverage probably more than any other months.

I hope to get my off-road truck back up and running this year. I’m planning on installing a lockup convertor overdrive transmission in my ’90 Dodge, which is equipped with its original Cummins engine. When I get the trans in, I’m planning on a 241/205 doubler, keeping the 4.10 gears and Detroits. With some 40-inch tires I think I will have decent road gearing with enough low ranges to be able to conquer most trails. Maybe in a couple years I could come with you on UA. Thanks again for the great mag and taking time to read my babbling.
Michael Miller
Lenox, IA

Yep, you were the first guy to mention “differential” and also the third email we received. Congratulations, Michael. Plates are on the way!

First Overall ID Winner
Were you visiting Furnace Creek Ranch? That sure looks like it could be the same diff gears as Old Dinah the steam engine. Yes? No? Am I close? Well, how many got it before I did? I’m clear out here in the middle of Iowa, but I think I remember you mentioning Furnace Creek in the tales of some of your sojourns. Anyway, it looked a lot like some old-time farm tractors I’ve studied up on over the years.
Jeeps forever!
Robert Kanagy
Via email

No one else ID’d the actual vehicle before you, and very few ID’d it as a differential even though my title was “What’s the Diff?”!

Almost the Whole Story Winner
In response to your 4xForward challenge of identifying the mystery picture in July ’11, I believe I have an answer. It appears to be a part of the geardrive system on Old Dinah the steam tractor. Old Dinah was a tricycle-type steam tractor with an upright boiler and geardrive that was used around the turn of the century (last century, not this century) in an attempt to replace a 20-mule team. The mules were used to haul borax from mines in Death Valley to the railhead. Unfortunately, she proved to be too high maintenance (gee, that’s not weird or anything) and was relieved of her duties after a short while and the mules got their jobs back.

As I mentioned, the gears in the photo are part of Old Dinah’s geardrive system, the part that acts as a differential to differentiate the power between the wheels. Part of the gear train is missing, but it would have been linked to the two pistons between the frame wheels. Once power was transferred to the main (larger) gear, the smaller gears inside acted much like spider gears in a conventional automotive differential to transfer torque to the wheel drive gears (one is pictured, along with the axleshaft to the far wheel; the other is simply on the other side of the large gear). More info about Old Dinah can be found at So, how about them plates?
Brenton Richards
Via email

Nice work, Brenton. Plates are on the way. Thanks for the link.

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