Over-Revved Truck Engine Sends Every Piston Through the Block, Obliterates Transmission

Parts of the bellhousing even blew through the passenger floor and window.

byNico DeMattia|
Over-Revved Truck Engine Sends Every Piston Through the Block, Obliterates Transmission

Anyone with even the slightest shred of mechanical sympathy has to wince at videos like this one. Redditor Conyers117 recently posted a video of a diesel engine from an International DuraStar work truck that was overrevved while going downhill and quite literally exploded, taking its Allison transmission with it.

According to Conyers117, the truck belonged to an electrical company and, while the driver was going down hill, its transmission somehow shifted into first gear. That immediately overrevved the diesel engine, which broke every rod and and piston, firing them through both sides of the engine block. Part of the transmission bellhousing also turned to shrapnel and, luckily for the driver, blew through the only passenger floor, even destroying a window.

It's unclear exactly what kind of truck it was, which engine is had, or how fast it was going downhill, so it's impossible to know how high the revs got before the engine turned into a frag grenade. Unfortunately, the engine's ECM was another victim of the obliteration, so the mechanics weren't able to find out how fast it went before detonation.

You might be quick to point to driver error, and that's certainly possible. However, according to Conyers117, the truck used an Allison automatic transmission, so it shouldn't have allowed a first gear downshift at speed. The driver also said the transmission did it on its own, so the thinking is that there was an issue with the transmission itself and not driver error. Although, that does sound like a six-year-old's excuse when something breaks—"It did it all by itself!"

This isn't as egregious as the driver that flat-towed a 2021 Jeep Wrangler in four-low and first gear. That was just ignorance, which sent a Pentastar V6 revving to an estimated 50,000 rpm, before it relieved itself of its pistons. At least in this case, the transmission's TCM shouldn't have allowed a first-gear shift, even if the driver tried to manually, so the driver could be off the hook.

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