Okay so when I have something in the back of my truck like my ATV for instance, from about 45-65 mph the truck will shake like hell. I don't understand it. When it's empty it's fine, literally all the way up to 100 mph. Brand new ball joints, complete brand new "HD" steering, brand new track bar, adjusted the gearbox lash, 10 ounces of counteract balancing beads in each tire, brand new shocks, brand new steering stabilizer. Everything is tight. I can't pinpoint the location, but it feels like the front is doing it. Any opinions? It even has some shake to it now that I put the fiberglass cap back on. It's only smooth when the truck is naked and empty. It didn't do this when it was little. Any ideas as to what else I can check?

 

I had heard that the balance bags are junk. Dont know if thats youre problem or not though. Does the shaking feel in the steering wheel or you a$$? If felt in the wheel its probably coming from the front, the other would probably be from the rear.

Is there any lift or stock height? Last time had an alignment?

 

Merc225HP chased a mystery vibration that would come and go for quite a while, and discovered it was his balancing beads causing it. Get the tires rebalanced with standard weights, see if the problem goes away.

 

It's got a body lift, but the suspension is at factory 2500 height. Sometimes I get it in the wheel, other times not. It's been aligned about three months ago. Ugh, that's gonna be such a pain, but if I have to I suppose I will. Those tires are so hard to get to seat. No shop was able to do it. Not even an 18 wheeler service shop. They tried using two bead cheetah's at once with no luck. I had to use starting fluid and a home made dump valve together timed just right to get the tires to seat and hold. those 16.5" rims are awful in that aspect.

 

If it comes and goes and changes from the wheel to seat, I bet the banance beads are the culprit.

Edit to add: the guy that works in the shop next to me had them. Ended up having them removed cuz he couldnt even get to 50mph with it shaking so bad. Got them removed and balanced "normally" and hasnt had a problem since.

 

Damn, it sucks cuz I'd say the first couple of months after I put them in it was as smooth as driving my 1984 Caprice Classic

 

if it is more predominate loaded or with the shell on versus empty, have a look at the carrier bearing. Lots of folks never ever ever check those things. That was problem with my Ford, loaded the shifter(5spd) would shake up to about50, then the seat would vibrate. Empty no symptoms

 

My truck has a one-piece rear Driveshaft. No carrier bearing.

 

well, that makes it more interesting. Have you checked the trans mount? Ujoints? Is the output flange fixed on trans or a slipper? Make sure it has not bottomed out when loaded.

 

All U-joints are brand new, trans mount is brand new.

FOUND THE PROBLEM THOUGH!
I added the steering brace that ties the two frame rails together and adds another bearing to the steering gearbox. I also upgraded from a rubber bushing to a polyurethane bushing on the track bar. Smooth as ever at all speeds now! Steers literally like a dream now too! If you turn the steering wheel 2 degrees, the truck responds! When turning into an uneven surface where the truck has to flex a little, the front end feels rigid and I love it! I find myself over-correcting unnecessarily now because I was so accustomed to the sloppy front end. I recommend the poly bushing and/or steering upgrade to ANYONE with one of these trucks (4x4 of course)