bullgear

That's the big gear on the front of the Crank shaft... also drives 2 other accessory gears... pretty important thingy.

 

10-4, if you are looking at a used truck this is one of the most critical parts of the engine that you need to check out before buying, if you own a DD and have over 500k on the truck get it checked out

 

bull gear.... i saw many bullgear problems on 14L, but not so many on 12.7. i do not really know why?

 

bullgear sits dead center of the front gearcase on a 12.7, 11.1 series 60, it is driven by the crank gear, and drives the cam gear, acc drive gear and the air compressor gear, they are known to wear especially as they near the 900k-1million mark, some sooner depending on maintenance, definitely something that needs to be documented and taken into account if buying a high mileage used truck. if you are referring to the new design Detroit diesel dd13 or dd15 series of engines, all the gear train is on the rear of the engine and there is no bullgear on those engines.