This bulletin applies to 2015-2019 Chevrolet Suburban and Tahoe, 2019 Silverado LD and 2014-2018 Silverado vehicles. Technicians may be unable to achieve pre-load when setting up the pinion bearing pre-loads during reassembly of the 9.5/9.76 inch rear axles. Reports from the field include breaking of sockets, breaker bars, ratchets and pinion holding tool without achieving pre-load. Chevy reports that they have also seen pinion gears with stripped threads.
The cause has been determined to be when re-using a pinion flange that has imperfections in the mating surface where the nut contacts the flange. In rare occasions it has also been experienced with a new flange as the nut and flange mating surfaces start to wear into each other with high pressure associated with drawing the bearing and flange onto the gear. When there is extremely high amounts of torque applied to the pinion but, it is possible to deform the nut, which starts the thread damage.
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To aid in assembly (in conjunction with Differential Drive Pinion Gear Bearing Replacement procedures in the service manual), with the pinion flange started onto the pinion gear, install washer P/N 11609638 onto the pinion shaft between the flange and nut. Tighten the pinion nut until you achieve 10 in-lb of rotating torque, then back the nut off and remove the washer. Note: 9.5/9.67 rear axles do not use a washer between the pinion flange and nut. Do not leave the washer in place!. However, the 9.6 inch axle does use a washer.
Tighten the nut back down until you achieve 15 in-lb for used bearings or 20 in-lb for new bearings. The washer can be used multiple times but if either surface of the washer becomes damaged, discard and obtain another new washer.