World’s Largest Mack Truck Is Driving Again After Major Restoration

The mighty M100SX is the biggest bulldog that Mack Trucks ever built. Only three examples were made in the 1960s, and just one still exists today. It was acquired by The Mahan Collection Foundation in New Jersey a couple of years ago, and I wrote a detailed story about the giant’s new shot at life after more than five decades. Now, the truck’s restoration is nearly complete, and it’s driving under its own power again thanks to the 1,788-cubic-inch diesel engine under the hood.

If you want the comprehensive backstory on the Mack—right down to its original build schematics and spec sheet—be sure to check out my write-up from 2024. In case you’re in a hurry, I’ll give you a brief breakdown.

The rig you’re looking at here shipped from the factory with a two-stroke Detroit 12V149T engine making 1,000 horsepower at 1,900 rpm. Original measurements show it spanning 32 feet and 1 inch from the front bumper to the back of the frame, and it’s 13 feet and 6 inches tall. It tipped the scales at 95,485 pounds without any bodywork, and the payload capacity exceeds 100 tons thanks to a GVWR of 331,875 pounds.

After several years of infrequent back-and-forth, The Mahan Collection Foundation was able to acquire the M100SX. It had sat for a long while at the Pile Foundation Construction lot in Far Rockaway, New York, on Long Island. Getting it back in running condition took nearly two and a half years, but clearly, it was worth the effort:

Mack M100SX rides again!

You can hear the big Detroit making noise with its unique center exhaust stacks. Because the engine compartment is far larger than the cab—it’s not even close—the operator sits off and to the right. And before you ask why they don’t let it run wide-open on the highway, just know that this truck only ever topped out at 28.8 miles per hour. The gearing is low and the movement is slow; such is the case with heavy off-road haulers like this.

I’ve reached out to The Mahan Collection Foundation for more information on the Mack’s restoration. Hopefully, I can bring you a more detailed follow-up that explains what went into the big job. One way or another, we can all be glad that a piece of trucking history is back in action. It almost brings a tear to a guy’s eye…

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