AC D21

D21 SERIES II owner: Boyd Miller - Savannah, MI photo credit: Tharran Gaines 26 SEPTEMBER/OCTOBER 2010 ISSUE 011

D21

The Model That Broke The Barriers B Y THARRAN G AINES

aving grown up on a

put the new D21 t o work at a

farm in nor th cen-

field day shor tly af t er it was

tral Kansas, I can

introduced in 1963, I had never

s till remember the fir st time

seen anything like the D21. Not

I saw an Allis-Chalmer s D21

only was it a mons trous ma-

tract or at the age of 13. I had

chine in size, but it could pull a

already spent plenty of time on

bigger load than mos t t eenage

a farm tract or going over

farm boys could even imagine.

summer fallow with a t an-

Maybe that’s why the D21 is

dem disc or V-blade behind

s till my favorit e tract or of

a Farmall 560. But until the

all time, even though our

local Allis-Chalmer s dealer

family never owned one.

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 first Allis-Chalmers tractor that produced more than 100 horsepower, 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 horsepower — 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 company that built only small tractors.

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

company’s first use of a direct-injection open-combustion-chamber diesel engine in a farm tractor and also the first to use a dry air filter. 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 Swinford, author of Allis-Chalmers

Farm Equipment 1914-1985 and a member of Allis-Chalmers’ marketing department for 30 years, “In addition to the advantages of direct injection, the engine featured cross-flow head design for improved volumetric efficiency, alternating valves for more even distribution of heat throughout the cylinder head.”

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Although the D21 was the last of seven D-Series farm tractors, 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 eyecatching 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 example is the large operator’s platform 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 field 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 find a more comfortable 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 28 SEPTEMBER/OCTOBER 2010 ISSUE 011

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.

styling, the D21also featured a new powertrain with an independent PTO integrated into the design. The constant mesh transmission offered four forward gears and one reverse gear.

A two-speed gearbox doubled all gears to provide the operator 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 AllisChalmers. 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 Series seven-bottom plow in both

semi-mounted and pull-type configurations. 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 traction 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 operation. 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 applications and/or draft applications, despite its high horsepower rating. 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 fitted with rear duals for heavy draft work. The wheelbase, meanwhile, 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, AllisChalmers also offered the D21 as an industrial model. The timing seemed to be right for such a tractor, too, since the United States was in the midst of significant 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 five to six years with partner Rodney Knott. “For one, it was the first 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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30 SEPTEMBER/OCTOBER 2010 ISSUE 011

A-C D21

owned by: Henry Kellenberger Jackson, MI

Photos by

PE SU R rm Po we

r

Fa

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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 different wheel and tire setup.

It wasn’t long, though, before Allis-Chalmers discovered that they had become their own competition 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 32 SEPTEMBER/OCTOBER 2010 ISSUE 011

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 OneNinety 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.

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 articulated tractors and after-market power front systems, AllisChalmers 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 mechanical 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 Swinford, Allis-Chalmers built and leased a total of ten units beginning 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 flow caused wheel spin and excessive tire wear, while too little flow meant the tractor had to push the front wheels, negating the advantages of front-wheel assist.”

Holding to its promise, AllisChalmers recalled the tractors and nine of the ten were converted 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 oneof-a-kind D21 II with hydroFWA,” he concludes. “It’s just another case of Allis-Chalmers being ahead of their time in tractor design.”

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