379 bouncing bad

I have a 2005 379X, i have a bad bounce at 50 mph then goes away and returns at 60 mph, very aggresive almost like the drives are hoping, the tire tred is stepping as the tire guy calls it. not bad loaded with 90,000 lbs, you can feel it mt, and will bounce you out of your seat on the BT. I have changed, steer tires, rear tires,rear tourqe rods, adjusted ride hight,install centro matic bal, all 6 shocks, no change. when slow rolling, or in traffic, you can feel a mild bounce, like an egg bounce.
i am thinking a C-4 charge may fix it.

 

I wonder if the 5th wheel was slid one way or another before the bouncing started. If the frame is "light" it could be beaming when the truck hits a bump. 45 years ago or so my dad had a Diamond Reo 10 wheel dump w/ an aluminum frame and Hendrickson biscuits. Couldn't hardly stand to be in it until they finally fish-plated the frame. Problem solved. That truck had a hinged hand hold on the center front of the hood that was spring loaded. Flip it up and you could get to the radiator cap w/o tilting the hood. The ride prior to the fish-plating was so bad that that hand hold would flop up and down a couple of inches against the spring. The frame would resonate like a tuning fork, flexing from the weight of the front of the dump box sitting on its mount and hammering it when unloaded. Back to the issue at hand, if the frame length was just right on these Petes, and the just right amount of weight is placed at exactly the right spot, call it the resonance point, you could set up exactly the sort of situation the OP and others have described. I think I'd start by "stringing" the frame to make sure it hasn't sagged over time.

 

I have a 379 X 244WB with the same problem, bounces around 47 mph and at 60-65 the faster I go it will reduce the bounce, I have replaced, all shocks,tires,tourqe rods on rear drives, adj air bags,installed centromatics on drives. Still have a bad bounce. I can feel it with a trailer, not as much. loaded with 90,000 lbs i can feel it not as much. C4 may be the only thing to fix it.Please any suggestions.

 

I replaced the cab air bags, the kingpins, bushings and shocks now ours is riding like a cadillac. I read on here once a guy had the same problem after alot of $$$$ he found it was his drive tires, hope this helps!

 

I've got same problem 379 97 short hood . Bounce at 55-70. Checked tires changed tires .ride hheight new bushings tire shop says out of ideas whats Nexted ? Bounce seems on right side can it be trans or rear ends

 

Check your shocks and cab air bags.

 

I have just replaced, the clutch & tranny still having ride issues about 58 mph and then at 62 mph, you can throttle into the hot spot and will bounce you almost out of the seat, seems like, right front drive. HELP !!! please!!

 

I repeat that many of these un-resolvable bouncing and hopping problems can be traced back to issues with the frame. This is particularly true of long wheelbase vehicles with light (5/16ths) frame rails. You can easily test it for yourself with a few chains and binders and a block of wood. Wrap a chain around the frame at the trailing end of the front suspension mount and another at the forward edge of the rear suspension mount. Use existing protruding bolts or hucks to ensure they remain in place under load. String another chain below the frame rail, connected to the two chains at either end and begin to take up the slackwith binders, leaving enough "belly" to place a 6 or 8 inch block of wood (or even thicker if available) beneath the frame rail at the approximate center between the two suspension mounts. Then, tighten the chain under the rail using the binders and spacer block to create a truss for that rail. Road test. If the bounce is gone, you've located your problem. The permanent solution is then to insert or fish-plate the frame rails.

 

Any update on your truck. I'm having the same issue of a bad bounce when hitting a bump