Hi, just bought a fifth wheel toy hauler (no toys yet) and I am having a wild ride with a bucking motion, not up and down but back and forth, surging forward and back.
2003 F350 Diesel CC LB SRW King Ranch 8000 Total weight
2003 Forrest River Fifth Wheel Sandpiper 32ft Tandem 8200 total weight, flipped axles, gooseneck adapter RV3 fully extended.

I put on shock absorbers on the trailer and that made the overall ride about 20% smoother but buck is still there.

Currently planning on replacing the stock Ranchos with Pro-Comp MX-6 adjustable shocks to dial in damping.

Questions:
1. Does the slip yoke problem figure into this ?
2. Any recommendations would be appreciated.

Thanks.

 

A problem with "bucking" is the road, not the truck.
I have 2 sections of interstate roads in my area that cause this problem.

 

I'm trying to visualise this - and I pray to God you don't have a crack in the structure of your gooseneck!

How heavy is it loaded, and have you had someone ride alongside in another vehicle to see if the gooseneck is bending?

What kind of shape are the trailer brakes and controller in?

How is it loaded? Forward or back heavy?

 

Fifth wheel to gooseneck adapter.. Pop Up - RV 3. new adapter. No bends. Brakes excellent, controller brand new. Loaded weighs about 8500 lbs. Front heavier. Concrete highways are worse wherever large bumps are. I get about 1-2 surges and then they stop.

Tried adjusting the adapter short to tall, no real affect.

 

Well you have done a couple of things to your trailer to amplify the problem:
1) You added a gooseneck adapter to a 5th wheel trailer
2) You flipped the axles on the trailer to increase height.

The gooseneck adapter increased the length of the connection at the truck, which leads to more leverage at the connection, this results in much higher loads/forces being generated at the truck connection and pin box. Hitch adapters/extenders are a very bad idea IMO, as they add increased loads at the truck and particulary the pin box that the trailer was never designed to see. Cracks and failures at the pin-box are common from these modifications.

By flipping the axles on the trailer you have increased the height & center of gravity of the trailer. This causes the trailer to sway & bounce around alot more over bumps do to the elevated CG.

So by combining the hitch adapter/extender and the axle flip kit you have amplified all the forces and movement on the truck and trailer. Since you have these mods, you need to pay extra attention to proper loading and weight distribution in the trailer, and drive at a slower speed. Also you need to frequently check the pin box and trailer frame at the pin box for cracks/breaks and other overstress indicators.

As you can tell, i am not a fan of hitch adapters/extenders and axle flip kits. These items were not in the original design when the engineer designed the trailer, so there effects and increased loads/forces were not taken into consideration when desiging the size of frame members and components and the CG of the trailer.
Yes i am well aware that many people have these modifications, but it does not make them correct. These modifications are a band-aid to an improperly sized trailer for the users needs. These modifications have really gotten popular do to the consumers wanting luxury/large coaches to go off road with. Unfortunately luxury/large coaches and off roading do not go together. However, the RV dealers want to sell the bigger trailers to the off road crowd so the modifications continue.

Sorry for the rant, you are going to have to live with a certain amount of increased trailer bucking/swaying do to the modifications. Load carefully, drive safely (read slower) and check the trailer frequently for stress cracks/breaks at the pin box area.

Good luck

 

Appreciate the feedback... Well understood... the flipped axles came with it. Despite these issues, I am trying to reduce their affect with shock absorbers on the trailer and adjustable shocks on the truck.

Again no swaying, only back and forth bucking. Due to the configuration of the trailer springs, frame and gooseneck, the up and down gets translated to back and forth.

If I do not get an acceptable amount of damping from the shocks, I may end up flipping the axles back over and lowering the gooseneck adapter.

 

Here is a link that will help your problem, http://www.sphitch.com .I installed a sphitch on my 37' open road and it stoped the "chucking" thats what most refer to the for /aft jerking.I was impressed with the hitches enough to become a dealer,if I can help you let me know.Poke around the site and look at videos,It works.

 

That hitch may help damp the jerking motion, but it does not address the main problems of Pin adapters and axle flip kits.

 

Opinions are one thing but the proof is in the pudding as they say!!!

 

I'd be scared to pull any rig with a gooseneck adapter on a fifth wheel. I just don't trust those things!

If it was gooseneck to begin with - that's fine. But an adapter is a J. C. Whitney approach to pulling a big load without the right equipment.

I just can't see anything good coming from it.

That adapter is the weakest link in the connection, and if it fails it would be disastrous!

You need a REAL fifth wheel mount.

 

How was the axle swap done? I have seen (bought a gooseneck trailer from a redneck in Indiana) the axles were mounted under the springs, not an issue if they were built that way. Problem with mine is they were not, the axles were supposed to be mounted on top of the axles and because he was to lazy (?) he just flipped the axles under it. This puts the magnet on top instead of on the bottom, when I hit a rough spot in the road the magnet would fly back and forth, applying the brakes momentarily causing a really bad jerk or bucking problem. Take a look at your axles and make sure they were put under the trailer the way they are supposed to be, they may just need to get spun around and new spring pads put on them. If this is the case be sure to pull the drums and inspect the brakes for excessive wear. The solution on mine was to replace the axles (they were bent from being overloaded), with torsion axles. Nice ride now, my tractor is happy

Just a thought, good luck
Toyman

 

You bring a GOOD point there.

The electric brake assembly should be flipped at the same time the axle flip is done - all of them.

The backing plates should allow that.

Elsewise the mechanism is not going to work like it was designed to.

There are a lot of ways taking shortcuts can wreck you...

 

The pudding is not going to change the physics and increased stress that a 5th wheel to goosneck adapter or pin box extension puts on a pin box that was never designed for the added length and force loads. And it will not address the higher center of gravity imposed by the axel flip kit.

Your standard gooseneck mount is fine for a trailer designed for a gooseneck at the factory but no one has made a retro-fit 5th wheel to gooseneck adapter or pin box extension that does not increase the load on the pin box beyond the intial design parameters of the pin box. All 5th wheel to gooseneck adapters and pin box extensions are a poorly conceived band-aid for a trailer not designed for the customers intended use.

 

Thanks a lot for all the info.... so far. Definitely gave me a number of options. I will let you know what I end up with.

________________________
2003 F350 Diesel CC LB SRW King Ranch

 

Thanks for all of the input...and the winner is....

Reese 20k Select Series Hitch... Rides much better now. I also went with MX-6 six way adjustable shocks on front and still waiting to install on the back. (on my F350) I am also waiting for current front tires to wear out. Total fixes = 20K hitch, MX-6 shocks (only two so far) and new tires (only two so far) cut down on the bucking significantly... I am still evaluating the 5er on doing a back flip.... lowering back to original configuration. This will depend on the terrain where we end up camping.
In summary, I originally wanted freeedom in the truck bed but the gooseneck adapter FOR MY SETUP simply would not work adequatelly for the family to enjoy the ride... again thanks.