60 mph bounce, what is this??? need help please

[zzman]

I just picked up my new trailer the other day (40' gooseneck float).

On my drive home I notice a bad bad bounce on the rear end from about 58 to 61 mph.

I have a (new to me) 04. 5 4door, long bed, 3500 dually, 2 wd, 6spd manual w/stock wheels and 3. 73 gears.

The bounce felt like a real bad flat spot on the wheels. It accures at the same speed each time. Also there is a simular bounce at 30 mph but not so rough. At both speeds it appears to be in rythum with the rotation of the tires.

I have not felt this without the trailer before. I have 60 lbs of air in all 4 rear tires.

Went by the truckstop to get a empty weight on rig. steer 4420, drive 5760 and trailer 6760. This is empty with a total of 100 gal fuel on board.

The truck is sitting about 1/4" to 1/2" from riding the helper springs.

I have not yet put a load on the trailer. There is no flat spots on the tires. The tires do not act as tho there are badly out of balance. I see no signs of out of round tires. All 4 tires are the same brand, tread and size.

What could be the issue here?

I did notice a small leak on the transmission rear seal.

Perhaps this is an old problem that I'm not aware of. The truck is a month old to me.

I would sure appreciate some of you guys expect advise here.

Thanks,

Ron

 

[HBarlow]

Trailers wheels/tires are not usually balanced by the manufacturer or dealer. Do you see balance weights on the trailer wheels?



Harvey

 

[zzman]

Thanks for responding,

no they aren't balanced on the trailer. The truck is what is bouncing tho.

When looking thru back window you can see the tailgate bouncing up and down from the trailer as well as feel it (it is violent). Looking at the wheels thru the side mirror, it doesn't seem to be the wheels bouncing.

I believe it is the truck, somehow the suspension I think.

I don't know but it is very dangerous.

 

[Rams-n-Hogs]

My 20ft bumper pull flatbed does this, too. It has something to do with the tires on the trailer creating some sort of harmonic, or resonance on the road. It doesn't do it when loaded. I usually just drive through it, or stay under it. I don't think it's dangerous, just nerve-wracking.

 

[MickeyMiller]

I'm leaning with Jim... . there is a section of Hwy 101 between LA and Santa Barbara that just hits the harmonics of my truck. Severity is speed sensitive, but the ocillation it there every time I drive through it. I find it is small sections in various places, but it goes for a LONG way in that LA - SB section.

 

[JCasper]

Our 18ft flatbed trailer does kinda the same thing at about 50 MPH empty. I usually drive through it and it's not a problem.



Sorry not much help here.

 

[zzman]

Thats good to know that others experence this too. But I'm not too sure this isn't dangerous. It's like riding a washboard, feels like the wheels are bouncing off the ground,(but they aren't).

I'm going to load my sons Dakoda on there and try that.

Thanks all.

 

[JCasper]

Thats good to know that others experence this too. But I'm not too sure this isn't dangerous. It's like riding a washboard, feels like the wheels are bouncing off the ground,(but they aren't).

I'm going to load my sons Dakoda on there and try that.

Thanks all.

Maybe there is a possibility that you have a bad tire on the daully and it's only noticeable with the trailer.



Just a thought.

 

[llotton]

You should check your driveline angles, with the truck and RV laoded. Could be that the center angle drops just enough that you have the problem.

Larry

 

[HBarlow]

There is nothing difficult about diagnosing this. If the trailer's wheels/tires are not balanced they are imbalanced and will bounce whether visible or not. The bounce will be transmitted to the tow vehicle and felt in the cab. Your first step should be to have the trailer wheels/tires balanced if for no reason other than preserving the life of the tires and wheel bearings.



Were you pulling on a concrete highway with expansion strips when you noticed the problem? Concrete highways are poured in slabs with expansion strips between. Concrete slabs sag/bow in the middle of each slab and will create a rough oscillation based on road speed and distance between axles. Cars and unloaded pickups usually don't feel it but when pulling a trailer you will. If it continues to shake or bounce after balancing wheels/tires try it on a smooth blacktop highway.



Harvey

 

[grasmo]

I think your trailer weight dictates that it is the boss ... if it has a littlr imbalance it will magnify it a bunch by the time it gets to the hitch ... . could be a tire out of round just a fuzz put some weight on the trailer tires ansd I bet it will go away. . Good luck and man what a driver you must be . . 40ft. whew!!!

 

[grasmo]

I meant to say over the trailer tires.

 

[betterthanstock]

The truck is sitting about 1/4" to 1/2" from riding the helper springs.

I have not yet put a load on the trailer.

Put a load to get those springs touching. Maybe they are hitting on the helpers making it seem like it's hitting something.

 

[zzman]

Well I loaded it down with a 15k lb backhoe, increased the tire air pressure to 75lbs. Didn't feel any bouncing at all when I hit 60mph. When it is empty the bouncing doesn't seem to be much at all in 5th gear, in 6th gear it is rougher.

Grossing out at 32k lbs, I can tell now I need a smarty I think.

The bouncing thing I can live with, it's really not as bad as I first thought.

Thanks for all the input

 

[LesStallings]

The first few loads I made with our 34 foot gooseneck included trying different hitching heights. In the beginning, the gooseneck was too long and the trailer did not ride level, especially empty. I would get a similar bounce to what you are describing. It was not really much noticable when loaded.



For my second trip, I lowered the front of the trailer one hole on the gooseneck and the ride was much smoother unloaded and it pulled loaded very stable.



I did try one more adjustment lower, but is did not improve the ride and put the front of the trailer a little too close to the sides of the truck bed so I went back to the previous adjustment.



I find that positioning the load on the trailer also has a significant affect on the ride. I shoot for 1,500-2,000 pounds pin weight. Even without weighing the pin weight, note how low the rear bumper on the truck is when it is towing smoothly and shoot for that height when loading the trailer. If the bumper is too low, you know the load is too far forward and if too high, the load it too far back.



Once you find the right combination, not only will the rig be more comfortable to drive, it will be much safer also.



You are pulling more weight than I am, so It will be a little slow. With your weight, I would certainly want 4. 10s for gearing.



Should you decide to go with a Smarty or some other box, be sure, REAL SURE to install an EGT gage. You will definitely have the capability to fry your engine if you don't monitor exhaust gas temperatures very carefully on a pull.

 

[zzman]

Great stuff Les, I think you have something there. The front of the trailer was about 1" lower than over the center of axles when I first drove it home. I adjusted it up to about 1-1/2" higher than the axles. Thinking it will level out when loaded. Yesterday's load was a little heavier to the front and it bucked all day long, a real kidney smasher.

Thanks for your reply, now things make a little more sense.

Great site.

 

[MountainMan1]

I tow RV's for a living and run into your problem now and again. It has always been the trailer, probably a wheel or 2 out of balance. I don't do anything about it except mention it to the receiving dealer. I just wait until I can unhooked from it and then can relax!



If you live in the mountains go 4. 10 otherwise 3. 73 or even lower if easily avaliable. When I tow I run my Smarty at mild torque and 60HP, which is sw 2 or 3. In this configuration I rarely come out of overdrive almost anywhere in the country at my tow cruise of 58 mph. I have water injection and still watch the egt's whenever on a long hard pull.



Enjoy,

Peter

Ham Radio Over The Road - W7LUS - Live Webcam with Free Chat

 

[grasmo]

I have discovered slowly and painfully what Les mentioned right off the bat. I pull a backhoe around and have discovered if I load it 2 inches too far forward it will cause the truck to buck and shake your kidneys out. With the very heavy weight you only have to move it backwards or forwards an inch or two to make a huge difference in tongue weight. If you find a sweet spot make a note of how much sag/ squat you have. I can not believe how smooth the ride is now that I know where the sweet spot is. But I am hauling the same exact load every time.