Shake while driving

[DVT873]

Check your motor mounts, especially the rear and your cab mounts. I am guessing you have an air ride suspension. Find out what your ride height spec is and how it is measured. Check loaded and unloaded. With age some ride height valves lose their ability to respond to load. Height will be in spec without a trailer on. Hook up a trailer and check it again. Out of spec will change the driveline angles and can set up vibrations.....I am aware of 2 smartphone based apps that can be used to find the frequency of the vibrations and the magnitude. I have not yet tried either. VibSensor is free. The other is NVH by vibratesoftware. NVH is $400. I am told that both are accurate. VibSensor is great if you are an engineer and can do your own interpretation of the data. NVH is aimed at auto and MD/HD truck and provides interpretation and help. Frequency varies based on the component. Magnitude point to how far out of balance it is. This information can narrow down the problem area. $400 is a lot but still less than the $5,000 Eaton/Roadranger system. Then there is old school. https://www.youtube.com/watch?v=weDiELpXlpk&t=21s I am told that this device can also be used to find frequency. Anyway look for simple first.