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Gear Oil Install

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One final note on the Tru Hi-9s: Proper break-in and lubrication are imperative for longevity. The axles must be filled with 85-140 nonsynthetic hypoid oil, and they must be filled to the bottom of the oil fill plug on the third member, not necessarily the one on the fabricated housing. The axles also need to be run at light load up to 500 miles with constant cooling in order to break in the gears, at which time the oil should be replaced.