please help. loud grinding noise going down the road

That's a good eye. Driveshafts should not shake hauling upgrade loaded. Now you got me thinking.

Shafts riding pretty and all is well do not vibrate or shake like you described. Now if you are in a scale house trying to halt the rotation of the earth trying to make a rusted trailer tandem slide... that shaft is designed to fail in a certain way before you break the rest of the really expensive stuff int he drive train.

 

I fixed it, thank you for oyur suggestion.
The air valve had to be adjusted

 

I am also experiencing the same exact problem described!! It began while driving from Nebraska to Missouri, had the support bearing replaced at loves in St Joseph, drove fine until I got to Florida and over time it came back and now the noise is just unbearable while driving on a flat road, it stops momentarily while going upwards on a small hill or bridge, once I go down it starts again. The engine brake for some reason helps reduce the noise or if I'm idling while driving. Can anyone expert please give me advice on what to do to solve this problem, the company owner is throwing much money in this truck and it's also affecting my work performance and focus, is this the power divider or is it the leveling valve as some say I cause some similar valve was replaced on the left front drive axles and it I don't believe that was the problem and will appreciate an expert response.

 

Just got done getting my truck fixed at Peterbilt in Bryan Tx, with the same exact problem. Leveling valve was bad, and had a small hole in one airbag. Changed out leveling valve,replaced airbag, now truck runs quiet & smooth. They also set the ride height on my truck. Basically the problem is caused by air ride system not riding where it's supposed to.

 

Just got done getting my truck fixed at Peterbilt in Bryan Tx, with the same exact problem. Leveling valve was bad, and had a small hole in one airbag. Changed out leveling valve,replaced airbag, now truck runs quiet & smooth. They also set the ride height on my truck. Basically the problem is caused by air ride system not riding where it's supposed to.

 

Just got done getting my truck fixed at Peterbilt in Bryan Tx, with the same exact problem. Leveling valve was bad, and had a small hole in one airbag. Changed out leveling valve,replaced airbag, now truck runs quiet & smooth. They also set the ride height on my truck. Basically the problem is caused by air ride system not riding where it's supposed to.

 

My truck is doing same thing. Grinding noise.
But it only does it in 13th gear.
Push clutch in and it don't do it.
You can feel it in the shifter.
Hit a big bump in the road and it really really does it even louder.

 

I have the same issue which I’ve been doing a lot of investigating and I have a high chance that I believe it’s the power divider

 

Same issue. Leveling valve replaced, clutch adjusted twice. Ride height adjusted three times. Still got 15-18 gear knocking loaded around 1450-1600 rpm and hard pull. Down hill and letting off throttle roaring noise like you would in bad ride height.

 

Hey did you ever resolve the issue? Im having the same thing with my truck.