Gears grinding could have been from incomplete engagement, possibly from a mis-adjusted shifter cable. The dogs will skip over the gears instead of drop into the pockets and engage once throttle is applied. Not a total death sentence for the trans on occasion, but not great to have it happen regularly.
4WD is engaged by slipping a splined sleeve over the input shaft and onto the splines for the pinion shaft. If these splines are not lined up, you will get the grinding noise. 4WD should only be engaged when fully stopped, and very light throttle applied to allow the sleeve to slip over the splines. The sleeve is spring loaded to be forced over the pinion shaft splines, but if too much throttle is applied, the sleeve just skips over the splines. Too much of this will knock the splines down on the sleeve and makes the problem worse.
Always best to drain the factory oil and use a higher quality 75/140 (or the 75/190wt Maxima that we sell) for the front diff and trans. Ok to use a 90wt oil in the winter time for colder climates (under 32º).
4WD is engaged by slipping a splined sleeve over the input shaft and onto the splines for the pinion shaft. If these splines are not lined up, you will get the grinding noise. 4WD should only be engaged when fully stopped, and very light throttle applied to allow the sleeve to slip over the splines. The sleeve is spring loaded to be forced over the pinion shaft splines, but if too much throttle is applied, the sleeve just skips over the splines. Too much of this will knock the splines down on the sleeve and makes the problem worse.
Always best to drain the factory oil and use a higher quality 75/140 (or the 75/190wt Maxima that we sell) for the front diff and trans. Ok to use a 90wt oil in the winter time for colder climates (under 32º).