5th wheel trailer "bucking"

[doneditt]

I recently purchased a new Chevrolet "Kodiak" C4500 Truck that was upfitted by Monroe Truck Equip.The truck has a 6.0 Duramax Diesel, Alison 1000 trans and Link "UltraRide" air suspension. It came with a turnover ball gooseneck reciever that I purcahsed a B&W RV Companion 5th wheel hitch that drops in. I am having a problem severe "bucking" of the truck and trailer when I hit 25mph and it stops at 30mph.If I power through it with more exelerator it isn't quiteas bad. At first the trailer was a little low in the back so I had the axels flipped to level it out with the truck. The same thing is still happening. Any suggestions?

[doneditt]

I recently purchased a new Chevrolet "Kodiak" C4500 Truck that was upfitted by Monroe Truck Equip.The truck has a 6.0 Duramax Diesel, Alison 1000 trans and Link "UltraRide" air suspension. It came with a turnover ball gooseneck reciever that I purcahsed a B&W RV Companion 5th wheel hitch that drops in. I am having a problem severe "bucking" of the truck and trailer when I hit 25mph and it stops at 30mph.If I power through it with more exelerator it isn't quiteas bad. At first the trailer was a little low in the back so I had the axels flipped to level it out with the truck. The same thing is still happening. Any suggestions?

You might want to check the driveshaft ujoint and/or drive shaft angle. Maybe something was bent or stressed during upfitting.

[Hitchhiker]

doneditt,

Welcome to iRV2, we're really glad to have you here as a new member and are looking forward to reading your posts about your RVing experiences and adventures. You'll find a great bunch of folks on this site who are very knowledgeable of RVing, the rigs we use, and the places we go in them.

As you'll see, they're eager to help and share their knowledge and experiences with others.

If I understand the set up you have correctly, your hitch looks something like this:



After studying what I think your hook up to be, I'm thinking your bucking may be a resonance of the spring rates between the truck and the trailer. I'll presume you've already experimented with the truck's air suspension as an effort to mitigate the bucking.

You may want to consider going with something such as a Mor/Ryde Pinbox on the fifth wheel to absorb some of the dynamic force.



Again, welcome to iRV2, we're glad you joined.

[Gas Man]

I saw a GMC dually pulling a 5vr and he had air bags on his fifth wheel hitch might be something to look into.

[John Harrelson]

The number one cause of any type of trailer to buck or Porpoise, is an unbalanced load..

Bucking, some refer to it as "porpoising", is usually caused by the trailer's cargo not being distributed properly throughout the trailer.

If the trailer is too heavy in the rear or the front, the trailer will tend to "Fishtail".

If the rear of the trailer is too heavy you can sometimes hear the hitch making excessive noise ....
IE: clanking and banging as the receiver and the pin fight to maintain contact with each other.

A trailer will "porpoise" if the trailer is balanced "equally" throughout it's length ..

by "Equally", I mean if the same amount of weight in front of the axles is the same as behind the axles.

To remedy the problem simply load the trailer so that about 15% more weight is in front of the trailer's axles.
This will keep a constant contact between the trailer's pin or coupler and the truck's receiver plate or ball..

Another thing that will cause a trailer to fishtail is not being level... A properly hitched trailer should be level at all times..

example: if the height from the ground to the bottom of the trailer is 10" at the trailer's rear, then the the same 10" height should also be at the trailer's front..

There should never be more than 2" difference between the two measurements.

Best wishes,
John

Webster's Dictionary
porpoise
One entry found for porpoise.
Main Entry: 2 porpoise
Function: intransitive verb
1: to leap or plunge like a porpoise <penguins...porpoise out of the water -- David Lewis>
2 : to rise and fall repeatedly
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.
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[Ray,IN]

Here's another angle;
Is the truck new to you or is it a 2006/7? Stock shocks are wimpy at best, they usually last about 20K miles. A high rate double action gas shock like Bilstein,or Monroe ranchos really make a huge difference. I agree with John's assessment, more pin weight is needed.

[RV Wizard]

doneditt, welcome to iRV2.com. It looks like you are getting some good answers. Good luck, let us know what you find to resolve the issue and enjoy the website.

[doneditt]

Thanks for all the good advise from everyone. After taking my son with me and letting him drive it I think I'm goin to go with "Hitchhikers" advise and try an air-ride coupler. I am looking into the "5th Airborne" coupler. When we were test driving the trailer it was empty, so I think that there was a little more weight up front with the kitchen and bedroom being there. I should take it down and get the axles weighed at the truck scales to make sure. Thanks again. - Pete

[GreatWhite]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">n the rear or the front, the trailer will tend to "Fishtail". </div></BLOCKQUOTE>

Question #1 for me would be.. does it do it all the time or only on certain types of roads. IOW, does it only do it on concrete highways or does it happen on asphalt also? If it does it on both.. the above solutions may work. However, if it's only on cement highways.. the issue is totally different.

Highways are like the waves in the ocean.. at least here in Calif. The expansion joints combined with the distance between them.. and the length of your wheelbase can cause a hysterisus.. I believe that's the term.. the bucking will take place on certain highways with expansion joint length A but not with length B. Same thing happens in the ocean with boats.. If the lenth of the boat is such that it bucks at certain swell length periods.. it likely won't happen at other times when the period is longer or shorter between peaks. This can be offset, as you found, with speed changes.. and there is nothing you can do.. reasonably.. to avoid it at the harmonic speed.

[xc-mark]

Two things to do , if your trailer doesnt have shock on both axels you should get some. the second thing is GM is known for having VERY soft shocks right out of the box! If you upgrade the truck shock this will help some but the trailer is the most important issue.

[Wayne Koehler]

One other thing to check on the bucking trailer is the clearance between the top of the tires and the wheel well. If there is not enough clearance to put your hand in, then as the wheels run over rough ground or the joints in the pavement, the tires may actually contact the bottom of the wheel well and then the result is a 'bump'.

This is from my own experience. Had to go back to the factory and the mor-ryde folks found that the trailer manufacturer had built the trailers without enough clearance. The factory fixed that problem, but I sold the trailer anyway. The wheel clearance was not the only 'design' flaw.

I now have a 5th wheel with the trailair hitch and our experience has been good. Still get some rough ride on long concrete roads with joints.

["007"]

Thanks for the info Waynek and welcome to irv2.
Check out the 5th & TT section below.
Enjoy the forums and post often.