EAST PEORIA — Forty years ago this month, the doors of a new factory just across the Illinois River from Caterpillar Inc. headquarters opened for the first time to reveal a radically updated and enlarged tractor that the plant had been built to produce.

Those first D10 dozers to emerge from Building SS in East Peoria were significant not just for their size — at the time, the model represented the largest and most powerful of Cat's most iconic product.

One design element in particular made the D10 noticeably different than its smaller siblings: the elevated sprocket and final drive. The circular component that lifted the track and changed its overall outline to a more triangular shape made its debut with the D10 and proved to be such a marvel of engineering that it came to be incorporated throughout the tractor lineup.

"It was absolutely revolutionary when we introduced it 40 years ago," said Al Kenworthy, a large tractor engineering technical steward at Caterpillar. "It was a stem to stern, top to bottom redesign."

That elevated sprocket lifted the final drive higher off the ground, away from the rocks and dirt where tractors work, extending drive life and machine uptime.

The elevation of that component also isolated the drive from shocks and impacts, and allowed for a variety of different undercarriages to shift the balance of the machine for specific components, making the tractor more customizable for specialized applications.

Less noticeable but no less significant to the original D10 was its modular design. Major components of the tractor are manufactured separately and assembled at Building SS for a first test-run of the machine with all its systems connected and intact.

The D10 can then be shipped almost fully built or broken back down to components and re-assembled elsewhere on site. The modular design also significantly reduced downtime for common drivetrain repairs.

"The ability to take big chunks of the tractor and assemble them was also one of the hallmarks of the revolutionary design," Kenworthy said.

The initial assembly can be completed in about 16 hours in East Peoria, where LeeAnn Silotto is one of the D10 inspectors working on the production line.

In one of the final stages before the first splash of diesel fuel enters the D10's 400-gallon tank and the 600-horesepower engine fires up for first time, Silotto checks the connections that make the machine work.

"I touch every washer, looking for loose washers, any loose connections, and any hose fouls — if they cross each other and touch together, that's unacceptable," said Silotto, who has worked on the line at Building SS for 14 years. "It was born on the high rise here, and it gets started here for the first time after it gets its fluids."

In the years since the D10 debuted, Caterpillar has created only one model that is larger and more powerful, the incrementally named D11, currently the top of the company lineup.

But the entire roster contains a critical element that was born with the D10 — the elevated sprocket that has given the track for the tractors its distinctive shape and improvements to productivity, efficiency, ease of maintenance and durability.

"All of those things were dramatically improved with the elevated sprocket tractor," Kenworthy said on a recent tour of Building SS as a finished D10 rolled off the line, destined for a customer in Russia. "This facility was built exclusively for what would become the family of elevated sprocket tractors."

Matt Buedel can be reached at 686-3154 or mbuedel@pjstar.com. Follow him on Twitter @JournoBuedel.