1998.5 Dodge 3500 4.10 axle dually 19.5 Eagle alloy wheels with new custom steel inner rims, bead balanced tires. new drivelines trans. mount, rebuilt NV4500, DNE od. 3" leveling front 2" blocks rear. vibration in rear noticeable around 55 mph - 70 mph. enough to shake the mirrors, bed welds cracking at rear, and jingle anything in door pockets. I have visited several forums with same issue but never heard of a resolve for this. This is NOT FRONT END, TIRE, OR DRIVE LINE ISSUE. Seems like every time I read about someone having this exact same problem there are dozens of helpful people pointing at everything but the actual problem. I can take my hands off the wheel at 100 and it tracks true, I just cant drive at 100 all the time. It feels like oscillation or out of balance in rear tires, but that's not the problem.  I have changed the tires, wheels balanced and re-balanced and nothing changes. I am thinking something in the rear end but cant pinpoint it. No leaks, good brakes, Bosch drums proper oil and LS additive. There must be someone that has actually figured out what this problem is. I have searched many forums about people with the same issue only to watch it turn into a hijacked discussion about what to do about a death wobble.  Any actual experience with this would be helpful.

 

My buddy has the same truck as you. Same issues too. He swapped out everything, same as you. I think the fix was a bearing was sloppy on one side of the rear axle. Was not really bad but enough that it allowed things to move. You should also check that 1 of your universals is not out of phase in the rear driveshaft. 

Regards chris

Thanks, I was actually headed for the axle bearings next. No phasing needed on drive line. Si x States just built and balanced me a bang up one piece when I installed my od this spring. So that’s a rule out. I hope that the bearings do it as I have read dozens of forums that all end up with solutions ranging from track bar to trailer hitches and have been wondering why no one seems to look a diff. I did read one reply somewhere that a guy had changed his rear end and fixed the problem. That’s a little too vague for me as I need to know what and why. I hate parts changers as I have seen so many supposedly qualified shops through the years  replace too many parts for people and then say it was a combination of all this instead of admitting what really happened was they kept throwing parts at it until the problem was found and repaired. That’s why I have  always done my own repairs   It makes a man think and do a little research before spending his own money. I have to admit though that I have replaced or rebuilt more than I have needed to trying to build what I want for the non- existent perfect truck. 

I had a Ford with a bad pinion bearing do the same shake. Check that.

Same issue, same fixes. Looking at possibly a bent axle or bearing. At very slow speeds it feels like truck is wobbling down the road. When i bought the truck, i had to get dif bearings replaced. Dealer said the bore was not correctly aligned for one of the bearings and they replaced all the bearings. I cant remember what bearing it was, seems like it was carrier bearings. This would probably explain my issue currently. 320k miles since they fixed it when it was new and under warranty. 

If you have the heavy valve extensions on the rear, if its a dual tire axle, take them off. I just did this on one of mine and it solved the vibration issue in the rear.

If this vibration is NOT "harmonic" and you're certain its tire/wheel speed related then what you can do is set the truck up on rear jack stands.

 

With someone in the cab at all times for emergency situations, start the engine and run it in gear while you watch the driveline and tire rotation.  You dont have to spin up the tires very fast either and you'd be amazed what you could see moving about.  The tires may be out of round or separating internally or externally and you're unaware.  Or rims not straight, drive line bent, lugs off center...etc.  Its definitely worth trying if you've exhausted everything else.

 

I had a RV trailer axle hub with lugs mounted off center from the factory.  I actually took a video of it spinning so people would believe me too.  Had to buy a new hub...

 

 @KATOOM has the best suggestion. I would set it up in a driveway or quiet parking lots so if for some reason it jumps the jack stands no one will get hurt nor damage occur to the truck or buildings. Have a man running the throttle in the cab and second man safely looking from ground level at everything spinning and see what is shaking.