This has been posted over on Cumminsfurum as well so sorry if its a repeat for a few people but I just wanted to get a broader opinion if possible:
Hey everybody! I tried reaching out about this a while ago but to no avail... I have a terrible knocking/ vibrating that appears under load starting between 1900 ish rpm and up through 2500 rpm. I have been able to replicate it with the truck stopped and out of gear though it is much fainter and through the same rpm range. Load appears to amplify it. I have had the truck since 2013 and bought it from the original owner who took meticulous records of everything done to it. He was a retired gentlemen who used it to tow his 5th wheel exclusively around the country. It has been happening since I bought it and seems to be harsher at some times more than others. The truck is slightly modified... all in the signature. I read through a lot of similar threads and found this one: 93 knock under load
This sounds dead on to what I have been seeing with the vibration in the pedal and everything. Unfortunately, it didn't seem to nail it to the wall to a symptom. IIRC I messed with the play on the crank and it did move a bit but I didn't have a dial indicator available so not sure where it sits exactly. I also have ATP Super damper on it that I put on during the compounds and didn't make a difference. The old damper was a little worse for wear. The valve lash has been gone through but I still need to check for a bent push rod possibly. I don't think its a U joint as RCCummins was explaining in the thread as I can replicate it at a stand still. So far (knock on wood) it hasn't had any ill effects other than the knock and vibration. I have put 30,000 miles on it myself. The truck pulls hard, idles smoothly, and starts right up every time. It's just really embarrassing and annoying while driving around town as it is really prominent outside the truck. Any body nailed this down?? Really want to fix this thing