First off, I own a half dozen trailers, which include a car trailer, 12 and 24' enclosed trailers, an equipment trailer, two boats.
My truck is a 2003 6.0L automatic supercab short bed 4x4 that's been garage kept with only 15K on the clock.
The issue at hand is with pulling the light equipment/car trailer I have.
At 18 to 35 mph, regardless if its empty or loaded and regardless of weight distribution, it bucks violently in this speed range. The bucking will start even at minimal acceleration and continue until I get rolling on a smooth highway.
It feels like I'm on a bucking bronco.
The trailer pulls fine on my other truck, (95 7.3L F350), and it weighs only 1180 lbs empty. The hitch I'm using is a load equalizing model and the trailer sits dead level at rest. I have three different sets of load eq bars but adding the bars makes the bucking 10 times worse.
I've tried adding as much as a ton to the front the trailer but nothing makes much difference. The truck pulls all my other trailers fine, even my full size equipment trailer which weighs in near 10K loaded.
The trailer that bucks on the F250 tows fine behind my other truck and I've even pulled it behind my 1990 F150.

I've tried raising and lowering the hitch, I borrowed a different hitch, added and removed tongue weight, and increased and decreased trailer tire pressure. The trailer tires are about a year old and are 12 ply Mobile Max tires on Dayton style rims. The truck has Rancho RS9000 shocks all around.
I've been to several towing centers and not a one can figure out why it bucks with that trailer.
I really can't figure out why it gets so much worse with the eq bars on. When I add the Eq bars, the bucking starts almost from the very start and continues to get worse as I gain speed. It bucks like a stick shift car with a new driver and there's nothing I seem to do that will lessen, prevent or stop it.

 

are you sure the car trailer has the correct size socket for the size of the hitch ball????
and is it working correctly.


like 1 7/8 and not a 2 inch.. only thing I see you did not address. NOT knowing what truck or trailer is using.

 

What do you mean bucks? Jumping up and down and twisting in circles?

 

Yeah me too,

I'm afraid your description of "bucks" isn't very useful in terminology. WHAT, exactly, is "bucking"? The trailer is hopping up and down, or side to side, or?

OR,

Is the TRUCK "bucking" and the trailer is not. And by "bucking", the *** end of the truck is hopping? The truck lurches forward/rearward when underway? Driveline chattering, or hopping?

Worse around corners?

If the truck that shows the symptoms is a short bed extended cab truck, what *exactly* is the truck that doesn't show the symptoms, long bed? Short bed? Crew cab? Dually?

 

After I bought my "new" car trailer recently I was experiencing a funny thing. As soon as went on my way I started to jump in my seat, like I was riding a horse...Been like that at the speeds up to 40 mph all the way until I got on the highway. I was blaming that trailer tongue was a little too high on the hitch, maybe 2-3 inches or tires were at 100 psi on empty trailer. Trailer has been sitting since I brought it home so I still will have to see how it will perform being leveled, loaded or hooked up to different truck.

 

Guess he didn't need any help, eh?

 

Apparently not...

 

I do like the wrong size ball for trailer setup like the 1 7/8" ball and should be 2" or even 2 5/16" but most of the time when you have more than 1 trailer or ball setup it is rare to get them mixed up?


The other thing does it have elect. brakes? Maybe (ONLY AS A TEST and empty trailer) pull the wiring plug and test. Thinking something could be funky between truck controller and trailer brakes?


Just thinking outside the box
Dave ----

 

My first thought was brake controller, would be to try backing off the gain. When accelerating I doubt it is a brake issue. If it is a 1,200 pound trailer I doubt it has any trailer brakes.

How does the pickup handle other trailers? What is the condition of the hitch? Is the ball tightened down? Is the shank the right diameter to the hole it is in? Is the hitch bolted down to the frame snugly? What is the condition of the hitch system?

What is the tire pressure of the rear tires on the pickup? What load rating are the rear tires on the pickup?

 

I think he posted the truck pulls other trailers just fine.
Also his other truck a F350 IIRC pulls this trailer fine.
So it is this truck and only this trailer that he has issues with.


I also think he said he use WD bars of different sizes & sway control and did not help maybe hurt if I read it right?


Would his truck have something like a "tow/haul" switch maybe turn that off?
Hold the trany in low gear to rule it out from "hunting".
Dave ----

 

I'll venture that if the OP owns and pulls 6 different trailers, he is well aware of the ball diameter needed.

 

The ball diameter is correct, it takes a 2 5/16" ball. I've disconnected the brakes to be sure its not an issue.
The trailer is hitched dead level.
When I say bucking, I mean it feels like I'm on a rodeo bull, the truck bucks up and down violently both loaded and unloaded only with this trailer on this truck. The same trailer pulls fine on another truck, and this truck pulls other trailers perfectly with no issue. I've tried raising the hitch, lowering the hitch, adding torsion bars at various settings, and nothing gets rid of the bucking. Raising the hitch to the point that the trailer is 10" or so higher in the front helps the most but its not a fix. Torsion bars make the bucking worse.
The truck is fairly new to me with super low miles so I've not had more than a few hundred miles of towing experience with it yet but its fine with all but this trailer.
It has four new tires, (Dayton type wheels) and I've tried various tier pressures. The tires have a 110 psi max rating on the sidewalls but I've run them at 50, 70, and 80 psi and it made no difference.

If I simply let the truck creep up to speed from an intersection, I can feel the bucking almost right way, the truck feels like the front wheels are bouncing up and down.
Its always been an easy to pull trailer, I've towed it empty behind my Ranger and it towed fine other than obvious stopping issues behind a small truck. I used a buddies three axle equipment trailer this weekend and it towed fine behind the same truck so the issue has to be in the combination of this truck and this trailer or the hitch length somehow. A buddy has a single cab version of my truck and his truck pulls the trailer fine with the same hitch. It feels the same around corners, and the trailer doesn't appear to be hopping or bouncing when this is occurring. I had a tractor on it the other day and about half way home I realized I left half a cup of coffee sitting on the running board of the tractor, when I got home, the coffee was still there, and hadn't spilled a drop. Yet the thing shook so bad I couldn't hold a conversation most of the ride home. The tires on the trailer show no wear or cupping, the springs are all in good shape and the wheel bearings are all properly adjusted and greased.
The trailer is a mid-deck design with a solid diamond plate deck, but its built with 2x4 tubing underneath. Its got two fold down 5' ramps at the rear and an 12k winch and battery on the tongue. With the winch installed, plus the group 27 deep cycle battery in the box, there's about 375 lbs of tongue weight. If I put the torsion bars on, in order to load the bars I'm actually lifting the back of the truck up. Its light enough that even my F150 tows it fine without bars though when empty.
The truck that has the issue is a supercab short bed, (141.5" wb), the other trucks are all regular cab longbed trucks with a 133" wb.

 

When you disconnected the brakes did you pull the 7 way plug out back or turn the controller off? If not the 7way I would give that a try. Feed back thru to the trucks system a cause?


So with the coffee cup on the load on the trailer and it made the trip I would think it is not the trailer but the truck.


See if you can have someone ride with you first so they know what this "bucking" feels like and where it happens.
I know not safe but maybe they ride in the bed also.
Then have them follow behind and to both sides over the same roads.


I would look for wheels moving more than they should.
Something like wheel hop / spring wrap up maybe a drive shaft thing?
Why only that trailer who knows?


Time to really start thinking out of the box.
Dave ----


Does the truck have a load level deal thing off the rear frame to rear axle? If so can you disconnect it for testing and take a ride?

 

Thinking if you know the trailer tongue weight (about 375#) and you have pulled the 7way plug and the bucking is still there what if you drop the trailer and add 375# in the bed of the truck still buck?


Dave ----

 

When I disconnected the brakes, I pulled the brake wire from the terminal on the tongue, it eliminates any chance of power going back to the brakes. I then jacked up each wheel and made sure there was no play or brake drag.
(I can move the trailer around the yard with a Harbor Freight trailer dolly so its not heavy and doesn't have any rolling resistance.

I did something a bit crazy today, but I needed to find out if it was coming from the trailer or the truck. I strapped a seat from an old truck to the trailer over the the front axle and had a buddy drive me around the block, he said he was being shook violently but I felt nothing on the trailer. I could see the front of the truck going up and down but didn't notice it looking down on the hitch. We didn't go more than about 25 mph and didn't go out on any major roads. I hopped in the truck after about a mile and drove back.

Weight in the bed doesn't seem to matter, it does it with the bed both loaded and empty. (I had an 800 lb garden tractor and a few buckets of chain in the bed on the last long trip and it bucked the same as it did heading out empty. Smooth roads are better, concrete roads with evenly spaced seams really get it going. There's been a few times where it almost stopped bucking completely on fresh, super well paved asphalt roads.
I don't see how it can be the truck, I towed a three axle 28' equipment trailer today over 250 miles. I was empty heading out, and had a 20' sea container on the trailer coming home. That trailer is downright heavy even empty, its a deck over bumper pull with a 2 5/16" ball hitch. I used the same hitch I use with my car trailer. It rode great the whole way with the exception of some wind issues on the bridge pulling the trailer around on the way home. The trailer alone is 2600 lbs, the container probably around 5300lbs give or take a few. It pulled that with no real effort and no bucking. It didn't even really hurt my fuel usage as bad as I had expected.
I had two spare tires in the bed, two boxes of tie down straps and two buckets of binders and chains, maybe 230 lbs or so.

The trailer with the issue is light, like I mentioned before, I've moved it empty several miles around town on back roads with my 4 cylinder Ranger pickup.
Its sprung pretty heavy, probably heavier than it needs to be but it was that way since new.

The truck has only 16,000 miles on it, it was stored for many years while I was working out of state. After working through a few issues from sitting its been flawless and I use it every weekend now. The truck is basically like new. The trailer was built in 1971 and was bought new by a relative along with an small Allis Chalmers tractor with a loader on it. The tractor weighs about 6200 lbs with loaded rear tires and a full tank of fuel. Its got an winch mounted at deck level on the tongue and two heavy duty 5' 5" long fold down ramps that have two side braces which secure them in the vertical position when traveling. The ramps can also fold flat on the deck when empty.
The axles are 6,000 lb Dexter 5 bolt open center type. Without the winch, the trailer is a bit tongue light when empty but it was used to carry that A/C tractor for about 10 years when needed behind a half ton Ford.