I have asked about the driving noise before, but I think I am able to describe it better after getting the engine quieter. I know diagnosing a sound without hearing it is hard, but maybe yall have an idea.

When driving below 20 mph the truck runs completely silent, like any modern car. Going between 20 and 25 there is a very loud grinding noise (a dull noise, not like gears clashing). The noise immediately stops when going off the throttle and rolling. Go on the gas again the noise is right back. Accelerating past 25 the noise gets quieter but is still there. Same as before, only present when accelerating/ holding the speed. Go off the gas, it stops and rolls silently.

When going through curves and just slightly stepping on the throttle the noise changes to a high pitch whine.

Based on the fact that it is only present when accelerating, I think that I can rule the wheel bearings out.
I also rebuild my trans, completely and the noise hasn't changed. I have driven the truck, shifting gears manually, keeping it in second and accelerating to the 20 mph mark. The noise is still present and the same. That leads me to think that I can rule out the transmission as well (please correct me if I am wrong)

The one thing that came to mind that would also explain the change in pitch when going around curves is the differential.

I am no expert on any of this so I thought I would ask if my train of thought makes sense, or if there is something I am missing

I am planning on getting my friend to drive the truck while I sit in the bed to see if I can locate the sound more. The weather is just not playing along right now.

Thank You

 

Block the tires so it will not roll, and put the trans in neutral, parking brake off. This takes all the strain off the driveshaft. Then get under the truck and grab the driveshaft at the rear near the diff and try to move it up and down. Also see if it's leaking at the pinion seal. Some of these rearends are famous for the large nut in the middle of the pinion yoke getting loose back there. Also check the u-joints. Twist the shaft while staring at the u-joints to check for play.

 

I replaced the U joints when I got the truck, both because I suspected them and because the old ones looked pretty crusty.

The pinion seal is tight and does not leak, but I will check for the up and down play in there right now.

Thank You

 

I just had this same sort of problem with a little Bronco I just put on the road. I was positive it was the driveshaft, but it wasn't. I messed with the pinion angle, no change. So I figured I would just keep driving it, till it got worse, and then maybe I could find it. After driving it for several weeks, I came to the conclusion it must be the rear axle. But I still wasn't sure. I checked it and could not find anything wrong from the outside. But I had another unit from a ranger pickup so I decided just to swap it in. Did that, and the noise went away. Not sure what was wrong inside the old rearend, but these things are difficult to troubleshoot sometimes.

 

I do have a rebuild kit for the diff and could get a set of gears. I was confident in rebuilding my c6, but I'll probably send the rear end to someone for them to do it because I am not sure if I am capable of setting the backlash correctly. I saw some horror videos on people chasing it all over the place with shims.