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2007 mack truck chn 613, 427 aset ac engine failure due to oil pump drive gear spinning loose on auxiliary shaft.when the vehicle began traveling down hill, the oil pump drive gear failed causing an immediate loss of oil pressure.the engine became a critical instrument in controlling the vehicle's down hill speed particularly the engine brake feature aka the "jake brake".the engine brake uses engine oil flow to operate.since there was no more oil flow, the engine brake was rendered unusable.at this point, the choice was to continue down hill and rely solely on the vehicle brakes to control the vehicle speed, or continue to use the engine without the added braking power of the engine brake knowing that the engine would be destroyed.the driver chose to destroy the engine and not risk his life or the lives of others.the dealer refused to repair the vehicle under warranty because the eecm indicated the engine's maximum allowed speed was exceeded.further investigation revealed the problem is inherent to all aset engines because the oil pump gear helix was changed for the new design engine.the auxiliary shaft direction of rotation was reversed and the direction of thrust on the drive gear forces the drive gear away from the rear bearing journal which it is nested against.older engine design had the direction of thrust toward the bearing journal which held the gear in place.any condition, (like an engine overspeed) that would increase oil pressure could dislodge the gear.according to the dealer, an engine overspeed condition can only occur while going down hill and using the engine to control vehicle speed.if the hill would have been higher, the engine may not have been able to continue to slow the vehicle and a crash would most likely have occurred.this happened in southeast louisiana where high hills are non existent.had this happened in a mountainous area, it could have been disastrous.mack trucks refuses to discuss this any further.