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DVT873

The arm on the valve should be level. Yours looks like it's tipped up. Unhook the rod and move the arm up and down. If the valve is working correctly, it should only take a tiny bit of movement at the end of the arm and you will hear air moving. These valves can go bad and not react when the arm moves.

This will change the driveline angle, and that in turn, can cause vibration/noise. This can be a "silent" transmission killer. Often, the vibration isn't felt or heard, but it is being absorbed, usually by the back box on the trans.

Nobody does it this way, but ride height should be checked unloaded AND loaded to confirm the height is correct and the valve is working.

Even if the ride height is correct, driveline angles can still be off. I once had a new Paystar show up with a growl/grind in the trans. I would have bet $50 (about a hundred today) the bearings were bad in the backbox. Before we could touch the trans Eaton support made us do a drive shaft angle analysis using a kit and program they sent us. Took most of a morning, partly because I had never done that in the detail they wanted. The frame angles, trans angles, fwd and rr housing and all driveshaft angles had to be entered. Driveshaft diameter, length and tube wall thickness were also needed.

Axle ratios and all the trans ratios, engine RPM. It was a time sucking PIA. Finally got everything in the progran and pushed the enter key. It spit back that the forward housing was down 1.5 degrees. Installed shims and went out a drive. The noise was gone. I was amazed.