AC D21

26 SEPTEMBER/OCTOBER 2010ISSUE 011

D21 SERIES IIowner: Boyd Miller - Savannah, MIphoto credit: Tharran Gaines

27SEPTEMBER/OCTOBER 2010ISSUE 011

aving grown up on a

farm in nor th cen-

tral Kansas, I can

sti l l remember the f irst t ime

I saw an Al l is-Chalmers D21

tractor at the age of 13. I had

already spent plenty of t ime on

a farm tractor going over

summer fal low with a tan-

dem disc or V-blade behind

a Farmall 560. But unti l the

local Al l is-Chalmers dealer

put the new D21 to work at a

f ield day shor tly af ter it was

introduced in 1963, I had never

seen anything l ike the D21. Not

only was it a monstrous ma-

chine in size, but it could pul l a

bigger load than most teenage

farm boys could even imagine.

Maybe that’s why the D21 is

sti l l my favor ite tractor of

al l t ime, even though our

family never owned one.

D21BY THARRAN GAINES

The Model That Broke The Barriers

Certainly, the Allis-Chalmers broke a lot of new ground in its time ... and not just in Kansas wheat stubble. Most notable, perhaps, is the fact that it was the fi rst Allis-Chalmers tractor that produced more than 100 horse-power, making it the largest tractor in the Allis-Chalmers line-up. Powered by a new A-C Model 3400 six-cylinder diesel engine, the

D21 had 93.09 horsepower on the drawbar and 103.06 PTO horse-power — putting it right up there with John Deere’s Model 5010, which was introduced the same year. As a result, Allis-Chalmers was no longer thought of as a com-pany that built only small tractors.

Not only was the 426-cubic-inch powerplant a new engine for Allis-Chalmers, but it was the

company’s fi rst use of a direct-in-jection open-combustion-chamber diesel engine in a farm tractor and also the fi rst to use a dry air fi lter. The engine also featured aluminum pistons and removable wet cylinder sleeves that offered a 4.25-inch bore and 5.0-inch stroke with a compression ratio of 16:1.

According to Norm Swin-ford, author of Allis-Chalmers

Farm Equipment 1914-1985 and a member of Allis-Chalm-ers’ marketing department for 30 years, “In addition to the advantages of direct injection, the engine featured cross-fl ow head design for improved volu-metric effi ciency, alternating valves for more even distribu-tion of heat throughout the cylinder head.”

SEPTEMBER/OCTOBER 2010ISSUE 011

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Although the D21 was the last of seven D-Series farm trac-tors, which began with the D14 in 1957, it doesn’t resemble the rest of the D-Series line. The D21 featured new, modern styling elements that were developed by a new industrial design department, which had recently been created within the company. Perhaps its most eye-catching feature was the large rectangular grille with chrome trim that complemented the smooth, squared lines. It looked tough even when it wasn’t hitched to anything.

Ironically, the new styling brought a number of features that would spread across the entire AC tractor line. One ex-ample is the large operator’s plat-form advertised to be “big as a ballroom.” Another was the full fenders that extended forward over the rear wheels to keep mud off the platform. On the D21, the fenders were even designed to incorporate two fi eld lights on each side, for better visibility, as well as improved styling.

Unlike previous models, the D21 also featured hydrostatic steering and a tilt steering wheel, as well as a suspended seat mounted on an inclined track. As the seat was moved forward, it was simultaneously moved into a lower position, allowing the operator to fi nd a more com-fortable work position. All were amenities that carried forward to the Allis-Chalmers One-Ninety, which was introduced in 1964.

Another feature of the D21was the large fuel tank which was now located behind the operator. The tank held 52 gallons, which was enough to run nearly 10 hours at 75 percent load. For most farmers, that was enough to go a full day without refueling at lunchtime.

In addition to a new engine, new comfort features and new

entire AC tractor line. One ex-ample is the large operator’s plat-

ballroom.” Another was the full

over the rear wheels to keep mud

the fenders were even designed to incorporate two fi eld lights on each side, for better visibility, as

Unlike previous models, the

steering and a tilt steering wheel,

mounted on an inclined track. As the seat was moved forward,

into a lower position, allowing the operator to fi nd a more com-fortable work position. All were amenities that carried forward to the Allis-Chalmers One-Ninety, which was introduced in 1964.

which was now located behind The substantial horsepower and rugged powertrain led to other challenges for Allis-Chalmers. The company didn’t have a line of implements large enough to match the D21’s work capacity.


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styling, the D21also featured a new powertrain with an inde-pendent PTO integrated into the design. The constant mesh transmission offered four for-ward gears and one reverse gear. A two-speed gearbox doubled all gears to provide the opera-tor with eight forward and two reverse gears. Most importantly, the powertrain was much larger and heavier than that found on the smaller D19.

The substantial horsepower and rugged powertrain led to other challenges for Allis-Chalmers. The company didn’t have a line of implements large enough to match the D21’s work capacity. Partnering with the LaCrosse Implement Plant, Allis-Chalmers quickly responded with a new line of equipment, including six- and eight-row A-C corn planters, cultivators and a new 9000 Se-ries seven-bottom plow in both

semi-mounted and pull-type confi gurations. The hitch on the semi-mounted plow could even be adjusted for on-land or in-furrow plowing.

As Swinford explains, “The larger semi-mounted plow was designed so that both rear wheels of the tractor could run up on the land and still have acceptable draft lines. On-land hitching also permitted the use of a wide single tire, providing equal trac-tion for both rear wheels, while giving the operator a level ride.”

The irony, however, is that the plow pulled easier and allowed the tractor to operate one gear faster, on average, when set for in-furrow opera-tion. The reason was that once the plow was offset toward the furrow, a reduction in landside pressure contributed to a lower horsepower draw from each plow bottom.

One of the selling points of the D21 was that it could easily be set up for row-crop applica-tions and/or draft applications, despite its high horsepower rat-ing. Standard tires were 18.4-38 singles on the rear with 7:50 X 20 tires on the front, although the optional 24.5-32 became quite popular due the wider tread. Even with 18.4-38 tires, the tractor could easily be fi tted with rear duals for heavy draft work. The wheelbase, mean-while, was a relatively short, 96.1 inches and weight ranged from 9,500 pounds to 11,700 pounds when fully ballasted.

In addition to the standard farm tractor version, Allis-Chalmers also offered the D21 as an industrial model. The tim-ing seemed to be right for such a tractor, too, since the United States was in the midst of signifi -cant highway and commercial construction throughout the 1960s. The only difference in the tractor was the color, which

One of the selling points of the D21 was that it could easily be set up for row-crop applications and/or draft applications, despite its high horsepower rating

A TRACTOR PULLER’S DREAM It didn’t take long, following its introduction in

1963, for the D21 to become a favorite among tractor pulling enthusiasts who had been looking for a powerful, lightweight tractor. Stripped down, the D21 could weigh as little as 9,500 pounds as a stock version, yet crank out over 100 horsepower.

Brice Terry, owner of Terry Implement, an AGCO dealership in Gallatin, Missouri, was one of the dozens of tractor pullers who took a quick interest in the Allis-Chalmers’ newest model.

“The D21 had several things going for

it that made it a good pulling tractor,” says Terry, who owned and ran a tractor called the Bounty Hunter for fi ve to six years with partner Rodney Knott. “For one, it was the fi rst

big tractor that Allis-Chalmers ever

produced. Plus, it was pretty simple to

make into a pulling tractor. You could

make the whole unit pretty light, or add

weight and move it into a heavier class.

In the meantime, the standard 426 cubic

inch engine could be stroked and bored to

as much as 585 cubic inches to crank out

plenty of power.”

“Finally, it had a manual transmission

without any hydraulic clutch packs, so it

was pretty simple to adjust and operate,”

he adds. “That’s why you still see a number

of D21 tractors running today. Even

some of those with new sheet metal are

still a D21 underneath.”

That was certainly the case in Winchester, Kansas, where Elvin Domann used a D21 as the base of his Hurricane Allis pulling tractor from 1988 until 2006.

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SUPER

Farm Power

Photos by

A-C D21 owned by: Henry KellenbergerJackson, MI


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“Back in the ‘60s, when the D21 came

out, it was quickly adopted as a pulling

tractor that ruled the roost for a number

of years,” he says. “The D21 was one of

the heavier built tractors in the industry;

so it stood up pretty well under pulling

conditions.”

Even after Domann rebuilt the tractor as a modern-day AGCO® Allis Model 9650 and later redesigned it into an AGCO DT Series model, it was still a D21 under the restyled skin. Unfortunately, Domann says the D21 frame and rear end weren’t able to handle the 3,000 horsepower level he is currently pushing in the Pro Stock class, which allows up to 680 cubic inches. Approximately three years ago, he parked the D21 chassis in favor of a component tractor he has named Hurricane Allis Category 2.

“I had no choice but to move to a

component unit,” he says. “I would guess

that we already had that original D21

engine up to around 2,000 horsepower

by the time we had bored it to 585 and

added a turbocharger. However, the

40 Series Detroit Diesel that we’ve

since gone to is currently at 672 cubic

inches and generating half again as much

horsepower.”

Still, Domann has nothing but respect for the original D21.

“I ran it for close to 20 years,” he says. “But as tough as it was — even though we

had reinforced the frame and drivetrain

— it was never designed to handle two to

three thousand horsepower.”

was a bright yellow enamel on the industrial version, and a dif-ferent wheel and tire setup.

It wasn’t long, though, before Allis-Chalmers discovered that they had become their own com-petition for D21 sales. With the release of the new, One-Ninety and One-Ninety XT in 1965, the D21 found itself outmatched by the new A-C in performance, even

though the XT was rated at 93 hp. The XT’s ace-in-the-hole was its new Model 2900 turbocharged engine, which could handle a tremendous amount of boost and extra fuel. As a result, many One-Ninety XT tractors were easily out pulling the D21 — especially after the engine had been “turned up” to as much as 120 horsepower by a knowledgeable mechanic.


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Allis-Chalmers’ answer was the D21 Series II, introduced in 1965. Equipped with a new 3500 Series engine, it was basically the same tractor as the original D21, except it was now beefed up with a turbocharger that pushed the power rating to 127.75 horsepower at the PTO and 116.41 at the drawbar. This gave the D21 Series II more than 15,000 pounds of pull, making it the largest tractor Allis-Chalmers had ever built.

Perhaps the most unusual feature of the D21, though, is one that remains elusive to this day. In response to the growing market for four-wheel-drive ar-ticulated tractors and after-mar-ket power front systems, Allis-Chalmers decided to test the market with its own front-wheel assist on the D21 Series II. Because the rear housing wasn’t designed to accommodate a me-chanical drive, A-C engineers developed a hydrostatic drive system. The pump was driven from the engine crankshaft and a vertically mounted motor

was used to drive each front wheel through a set of bevel and reduction gears. Control valves even allowed the operator to control the wheel speed from the tractor seat.

According to Norm Swin-ford, Allis-Chalmers built and leased a total of ten units begin-ning in late January 1967. As part of the lease, Swinford relates, Allis-Chalmers agreed to convert each of the tractors back to two-wheel drive if the company determined that the program was not completely successful.”

Unfortunately, that proved to be the case. As Swinford explains, “Too much hydraulic fl ow caused wheel spin and excessive tire wear, while too little fl ow meant the tractor had to push the front wheels, negating the advantages of front-wheel assist.”

Holding to its promise, Allis-Chalmers recalled the tractors and nine of the ten were con-verted back to two-wheel drive. However, according to Swinford, one user liked the tractor well enough that he refused to give it up, even though he realized that replacement parts would be unavailable in the future.

“So somewhere out there in someone’s collection, fence corner or wrecking yard is a one-of-a-kind D21 II with hydro-FWA,” he concludes. “It’s just another case of Allis-Chalmers being ahead of their time in trac-tor design.”

Documents

AC D21