Hey I've been searching around here for awhile but cannot find a answer. I have 2018 screw 3.5 and tow about a 7500lb trailer. While I am accelating hard or towing up a large inline say at like 80km/hr I have a horrible vibration/shudder that even my wife feels in the truck. Seems like the whole thing is shaking? I plan on taking to the dealership some day in the next little while. This can even be felt if I floor it with just the truck unloaded but not near as bad. The trailer really amplified it. Any ideas?
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I feel or sense a slight "coarseness" under hard acceleration in my 2018 HDPP, EB 3.5, but it is definitely not a vibration. I have almost 14,000 miles on mines, so I'm keeping an eye on mines while it's still under warranty.

 

Yes I would say that about mine when not towing. Throw a trailer behind it and its way worse. Like a vibration or surging.

 

A bad pinion angle will do this. If the angle gets worse when placing a load on the suspension, the vibration gets stronger. It can also be the opposite, the angle can be improved when loading the suspension, depends on what is failing: rear springs, transmission mount, engine mounts, etc.

A bad u-joint will also express itself more under a higher drivetrain load.

 

Axle wrap? If you YouTube videos of drag race trucks and traction bars you can see it in a more violent form.

 

Ya I'm not sure if it's drivetrain or engine. Have to do some more pulling. In the mean time I am going to replace my plugs. Been reading these 3.5s are hard on plugs and I am at almost 50k km.

I'm not sure it would be axle wrap at 80-90km/hr.
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130lb-ft per liter, 18:1 effective compression. If they weren't hard on plugs, physics would probably lose it's mind.