Need Help - Problem pulling a trailer

[c-hawk]

I'm hoping someone here can help me figure this one out... I've searched and haven't found anything that sounds exactly like what i'm experiencing.



I picked up a gooseneck trailer the other day. It's 20ft, with a 5ft dovetail, tandem axle. The thing is, when i'm pulling this trailer i get a strong bucking vibration, but only at 62-68mph.



Here's what i've found so far:



-It happens whether coasting, running on flat ground, or pulling a hill.

-Doesn't matter if I'm in 3rd or O/D (not related to RPM)

-I can even let off the gas completely, or put the truck in neutral while at those speeds, and it will shake.



-Below 60mph it pulls perfectly smooth

-Above 70mph it pulls perfectly smooth



-All of this was unloaded. So today I put my friends 01 Ram 1500 QC SB 4x4 on the trailer, and it was much smoother than when unloaded. Still had a bucking surging vibration (for lack of a better term), but it was not near as drastic.



-One other thing i noticed, when travelling at 65mph, which is the worst speed, and with the vibration going at full force, if i hit a big bump, it will stop the vibration immediately. But then it will start to pick back up again right away, till it's back to full force.



I'm thinking it has to be truck/trailer suspension/wheel/tire related, but i don't really know. Any help or suggestions would be much appreciated.



Thanks,

Chris

 

[klenger]

Aerodynamics?

 

[Fred Swanson]

No, I'd have the trailer tires checked. I have a 30 ft tandem dual gooseneck, and get a slight bucking. Tires are not balanced even new, but you may have a bad tire, depending on how worn they are. Check pressures, too.



Is it a 14K rated or 20K rated trailer. Either way, they want a load on them.

With a heavier load, it calms it down. Also, remember, the hitch weight is heavy, check your rear tires on your truck too.



Mine is very noticeable about 75 MPH but is gone by 80 mph.



Once I found the offending tire, it smoothed it out nice.



How much does it squat the rear when loaded down, too.

 

[mbaston]

I had one of those problems. I looked in the mirror and the tire was so bad, the trailer, empty, was bouncing into the air.

 

[fox]

Probably is nylon tires. Move the trailer 1/2 tire rotation 30 minutes before the trip starts. These tires will "flat spot".

 

[QRTRHRS]

Is your ball slightly forward of the center of the axle? It should be. I think optimum posistion is about 6" forward of center. Anyone else?

 

[c-hawk]

Thanks for the replys. I'll try to answer all the questions.



The trailer is a 14k, has two 7k torsion axles on it. Tires (and trailer) are almost brand new. Can't even tell it's ever been down the road, or used.



My hitch is a B&W, and it's installed exactly as their instructions describe. It is about 6 inches ahead of the axle.



I can't look in the mirror to see if the tires are bouncing, because when it starts shaking, it's so bad everything in the mirrors looks to be vibrating and blurry.



Sounds like it's most likely one or more of the trailer tires. I'll try to check them out and see what i can find.



Any other comments would be appreciated.



Chris

 

[QRTRHRS]

Torsion should give you a better empty ride of springs. Like mentioned before, pull your tires and have them balanced. Check the air pressure. Try to match the pressure to the expected load. Frame rails are like a bridge, they will have a natural frequency of vibration. Your speed has apparently found a harmonic (imbalance). If you get the pressure/balance issues covered, maybe try different tire pressures on the front/back trailer axles. Also, make sure you have no brakes hanging up or and check the trailer wheel bearings for proper adjustment.



One other thought. If the tire balance and air pressure are correct, do you have a friend with a LWB Ram? If not, ask for help. Perhaps the trailer itself is the problem due to the axle placement, etc. Don't take the results as the end of the world. See what happens and post the results.

 

[Stranger]

Try this

Put about 6 bags of sand at the very front of the trailer

 

[amillstream]

I've pulled 3, 14000 GVW 20+5 dovetail (2 7000 torsion axles) and one of those fairly regularly untill I bought a trailer of my own. All of them pulled so smooth at any speed, loaded or unloaded that I tended to forget they were there! I would definatly check the tires and if that didn't help, try a friends truck to see if it could possibly have something to do with your truck.

Now hook to a 20000 GVW spring axle trailer and it will let you know it is back there! (Especially if you let mud freeze between the dualls! Talk about vibration!)

 

[SMorneau]

I have read about this on some of the RV sites. Some good advice is given there, as well as above. It sounds like wheelbases of trailer and truck, hitch position, loading, pin to axle distance on the trailer are all factors. If your trailer has movable axles you may want to shift them and see what happens. Airbags or different shocks may help but I wouldn't count on it.



There was a post about the T-rex suspension system on this site that discussed bucking in detail. The designer of that system really seemed to know his stuff maybe he could shed some light on this issue.



FYI, the tollways around Chicago make my truck and slide-in camper buck like crazy only a speed too fast or too slow would get it to stop. I thought the rig would self destruct and truthfully it probably would have broke something if I had to drive wrong speed.

 

[Tcolesanti]

If the trailer has a "walking beam" type suspension, even a wheel/tire that is slightly out of balance can start a shake/shudder like you are explaining. Even the suspensions that have two separate spring packs that are linked in the middle with a floating shackle will do this. My advice to you is to have all the wheels/tires high speed balanced and have the shocks changed to ones with a stiffer dampening rate.

 

[rlyons]

Check for water in the tires. I have found that a few times. A trailer tire is sometimes mounted long before the trailer is built or sometimes it will go flat on the lot and collect water or even get it from a very wet compressor. You should see what happens when it freezes. :--)

Roy

 

[c-hawk]

Well, I still haven't figured it out yet. I had the trailer inspected today, so i can get tags for it. I had them go ahead and balance the tires while it was there. They said it took a lot of weight to get them to balance. When i looked at the wheels, i was like :--) they weren't kidding. They have a ton of weights on there. Well, it made no difference. The trailer still does the exact same thing. It's no better, but i don't think it's any worse either. I do think it has something to do with the tires or wheels, but shouldn't it have made the difference when they balanced them?



I talked to the trailer manufacturer, and they suggested the water in the tire scenario. Shouldn't something that obvious have shown up when they tried balancing the tires?



Thanks for the help so far. Hopefully i'll get this resolved soon.



Chris

 

[MMiller]

Did they say the tires were ROUND? tires can be balanced and still be out of round. If the water was froze maybe. Or maybe they go tired of balancing and said good enough? Were the rims true? A buddy of mine that works in a tire shop has found many new rims to not be true.



Michael

 

[QRTRHRS]

Hmmm, what with the cold temps lately, do the tires pick up a flat spot? I would expect a thump thump kind of reaction though. What for tires do you have anyway? The weight thing sounds kind of extreme. Have you had someone else pull the trailer yet? Keep us posted.

 

[c-hawk]

Thanks for all the ideas. I'm going to mess around with it some tomorrow, as long as the weather is ok. I'll let you all know what i find out.



Thanks,

Chris

 

[OTRPU]

I've delivered alot of Gooses, usually in stacks. Had a stack one time that seemed like the column that mounts to the ball was somewhat springy. Like it would pull away from the mass of the trailer, then the rest of the trailer would surge forward with a bit of a bounce. Had more than a few gooses do this. Don't know if using a larger diameter column would prevent it or not. It's like the post would deflect then when it reaches a point the rest of the trailer snatches forward. Maybe this is what your feeling.



Cheers,

Steve J.

 

[Firewalker]

could also be a bad bushing in the torsion axel!!!

 

[c-hawk]

I'd like to say thanks again to everyone who offered advice.

I took the wheels off the trailer, and took them up to one of my friends who works at a local shop. Keep in mind that i had just had someone balance the tires, and that didn't help at all.



So i took them up to him to see if he could do anything. He couldn't believe how poor a job the other shop had done balancing the tires. He took 17ounces of weights off one of the tires. None of them were balanced, and one was 9oz off, still, even with the other shop's balancing job still on there.



So he stripped off all the weights, broke the beads on the tire and checked inside to make sure everything looked ok. It was. The really bad tires, he turned on the rim, to try to get them to cancel out to an extent. When he was finished, they were balancing out, but still took as much as 8oz. He also noticed that a couple of the tires appear to be slightly out of round, which was noticeable when they were spinning on the balancing machine.



So when i put them back on the trailer, it was noticeably better, but still not perfect. i think i can live with it for now.



Appears that the culprit is cheap tires. Oh well, guess i'm stuck with it for a while. At least it's bearable now.



Thanks,

Chris