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September 2011 InBox - Letters To The Editor

Posted in Features on September 1, 2011
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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.

Figuring Tire Pressure & Contact Patch
In the July ’11 In Box, Jay Siller asked about the correct tire pressure. He said, “Would somebody please just admit the answer is ‘Due to all the variables … we don’t know.’” It is true there are many issues that come into play to determine the ideal tire pressure. The weight of the vehicle and the size and rating of the tire make it impossible to give a specific pressure. A set of 38-inch tires for 17-inch rims can hold up a very big truck. Your reply reaffirmed that there is no ideal pressure. But there is a test you can do to find the ideal pressure for your vehicle.

Place some masking tape across the thread from the inside edge of the tread to the outside. Drive a mile or so. If you wear off the tape evenly, the tires are at the correct pressure. If you wear off the outer edge first, you have too little pressure. If you wear off the inner edge first, you have too much pressure. You could do the same test with a chalk line but you wouldn’t drive as far to wear it off.
Dave Norman
Via email

Right you are, Dave. Even wetting the driveway and rolling across it works for a good guide to on-street air pressure. I usually drive in the dirt then on the pavement to get an idea.

Ford Follies
Concerning the June ’11 issue, page 53, caption 3: The owner “wanted to keep the original 400M engine.” This truck started out life as a ’67 Ford F-250, according to the article. Ford did not produce the 400M until 1971. Nice truck, but the engine would not be original for a ’67 Ford.
Richard Grantham
Ocala, FL

Right you are, Richard, but was anything on this truck matching, or really a ’67? Really?

Ultimate Adventure EcoBoost F-150 Idea
Since you’re planning on using the new Ford F-150 with the EcoBoost engine, I have a challenge for the staff when it comes to building. Build it without deviating from the factory design— i.e., if it has an IFS setup, keep it. Use parts to gain the flex and strength you need, but keep it IFS. Keep the EcoBoost engine. That way people can see that you can take a truck, not deviate too much from the manufacturer’s original design, and still conquer a whole lot. Up for the challenge?
Jeff Osterhoudt
Via email

Good ideas, Jeff. Check out the build and see what we are doing. Are you a spy?

Stinky Product or Staff?
In the July ’11 issue on page 100 (New Products) in the description of the JK Freedom Top Headliner, what is this new pee-and-stick adhesive you speak of? You know, I guess I would be OK with that as long as it worked well, but I think I will draw the line at poo-and-stick adhesive.

Love the magazine, guys. Keep up the good work.
Jon Blackwell
Edmond, OK

Wow, that one leaked through!

Submission Information

4-Wheel & Off-Road welcomes letters to the editor. Letters must include an address or a telephone number so the sender can be verified. Once verified, your name may be withheld at your request. Letters published in this magazine reflect the opinions of the writers, and we reserve the right to edit letters for clarity, brevity, or other purposes. Due to the large volume of mail we receive, we regret that we cannot reply to unpublished letters or return photos. Digital photos must measure no less than 1600 x 1200 pixels (or two megapixels) and be saved as a TIFF, an EPS, or a maximum-quality JPEG file. Write to: Editor, 4-Wheel & Off-Road, 831 S. Douglas St., El Segundo, CA 90245; fax 310.531.9368 Email to:

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