I put 140 in the front diff just because there was plenty left over from the rear. I don't see how it could hurt it once it warms up it does the same thing as the 90 weight. I don't ride flat out either mostly trail riding. Unless someone says definitely do not run it I'll leave it in there.
Probably you won't have any problems but a 140 grade is harder to move inside the differential so need more power and another thing is 75w-140 is much more expensive than 75w-90 so get a bottle of 75w-90 and you will have enought for two changes in front,the 75w-140 for your transmission and rear differential:smilietwocents:.can i run 75-140 dif oil in the front dif to, so instead of buying two different weights for gearbox and rear diff which is rated for 75-140, and the front which is rated for 75-90. ? why couldn't i run 75-140 in the front also?