Mpostelli

I have a 2500 with the manual 4 wheel drive shifter. When the weather started to drop to 0 degrees and I was plowing I started to have these issues with 4 wheel drive. First started to knock a little, similar to when trying to turn to sharp when in 4 wheel. Now intermittently getting gear grinding, mostly reverse when under torque. Usually following plowing and surely a lot of snow gets packed under the front. Seems to come and go. Are my fears shot or is it just the snow and cold causing this?