Whenever I have issues i just can't pin down... I always come to the guys that I know have the most experience! This Pete has a Cummins ISX15 425ST with Eaton Fuller 10 speed, dump truck. Empty, she runs great. Full, I get this noise when going down grade off throttle, and only in top gear. She doesn't grumble when I try to recreate the issue in any other gears or when empty. Anyone know what this is? Also... the front leaf shackles have slop that makes the front axle bang side to side on weight shift... What does it need? Shackles? Shims? Bushings? Thanks guys.
It also stops when I push the clutch in or take it out of gear.
Have you done a plug check on the transmission?
Air suspension? If so is the ride height correct?
Not yet. I did drag a 10t loader on a 5t trailer with 5t in the box... no noise. So it seems to be a box load weigh caused issue, not a gvw issue.
Ride height is correct and stable.
Driveline angle when loaded/and or center bearing, 55 to 65. Driveline out of balance 35 to 45. Grumbling in top gear only is usually loose yokes- driveline related. But checking for metal on fill plugs would be first. Shackle pins and bushings plus rear spring hanger bushings.
Heavy rumbling barely off the throttle always made want to check drain plugs on the rears like TS mentioned. I'd do it soon.