Jerking Motion

[justrave]

We purchased a new 2005 318BHS 5th wheel in November. I noticed on my way home from the dealership, it seems that the truck had a jerking motion. This seemed to occured over rough highway coming down the Interstate. It almost seem that the truck did not have enough power but I know this was not the case becaused I maintained 60-65mph down the Interstate. It did not have the jerking motion the 75 mile trip. Is this the nature of the 5th wheel?

[CountryGuy]

justrave,

Have you tried towing since bringing home and loading with gear?? That might help a bit.

Sounds to me like you are describing actions caused more on concrete highways, some call it a porpoise action, back and forth, back and forth.

Some of this action can be elimiated with the use of airpin or like hitch attachments. Trailaire, Isolator and the MorRid (not sure that is spelled correctly) are some of the ones you could look at. These have been discussed a few times here at MOC, use the search engine (see top of page) to help you find the threads.

I am sure that other MOC members will come along and have lots more suggestions! Oh, and welcome to the forum!

Carol

[sreigle]

Hi justrave,

What you are feeling is common on concrete highways regardless of the brand of fifthwheel and truck. I've heard it explained that it happens when there is the right relationship in distance between the concrete strips on the highway and the wheelbase of the truck/trailer. It does not occur on all highways but it sure is annoying when it happens.

Sometimes driving slightly slower or faster will reduce it significantly. Sometimes shifting weight so that more is on the pin or less is on the pin will help (with a fifthwheel it is recommended that pinweight be 20% to 25% of total trailer weight). You can accomplish that by adding or reducing water in the tanks, depending on whether tanks are in front of the axles or behind. You also can raise or lower the trailer's nose by adjusting the hitch or the pinbox. That will shift weight onto or off the pin.

If none of that helps, then Carol's suggestions are possible solutions.

We don't experience very much of this with our current setup but we do occasionally get some of it. We got considerably more of it with our prior fifthwheel.

Hopefully someone will have some additional help for you. I remember well how annoying this can be. It also can be tiring on long drives.

[Native Tex]

Steve is right in his assessment. Sometimes you will just a bucking action due to the joints in the concrete interstates. The weight distribution will help. Be sure your fresh water tank has water to add weight to help balane the weight. Be sure to check your tire pressure on regular basis too. When you get on a good asphalt road you should notice a big difference, but most Interstates unless they have been resurfaced will have joints. When we went to a longer tow vehicle, it helped tremendously too.

[Dave e Victoria]

What you are feeling is due to the way a fifth wheel is connected to the tow vehicle. The hitch point is way above the rear axle. So, any movement of the truck to from level gets translated into a fore/aft jerk. The right pattern of highway irregularities can make the action really annoying and even dangerous.

You will find that loading up the trailer will help especially as you increase pin weight. But, rough roads will always increase the problem. As others have said, go back through the threads to read more about this. Trail air and Morryde offer pin boxes that go a long way toward elminating the problem.

Also, please note, this is not a Montana problem. It will occur with all fifth wheels. It is a problem of geometry. It cannot be fixed with airbags although they may help a little. Longer wheel base tow vehicles will help some. The only real fix is to provide an elastic connection in the fore aft axis. This is what the Morryde hitch pin does.

Bottom line, load up your trailer and try it out over the roads you usually travel. If it is still annoying, think about getting a Morryde pin box.

[trukdoc]

What kind of truck do you have? My 2005 PSD 6.0 has a jerk to it when RPM is low and Load is at max. I think it is the computer cutting the eng back. I notice a fluctuation in the boost guage. If I let the transmission downshift it straightened out.

[sreigle]

Trukdoc, ours doesn't do that. I'm curious what's causing that.

Dave, where I think airbags might help a little is by raising/lowering the rear it shifts trailer weight and changes pinweight. It helped us quite a bit on our '99 truck and 2880RL but we may have just been fortunate that it helped. I would not suggest airbags to eliminate this problem. The hitch changes would be the better choice for that, as you mentioned. But we already had the airbags to level the truck so used that tool to help with the jerky motion. Our 3295RK is less prone to that motion, even when towed with the same truck so the weight and pinweight differences you mention seem to fit our situation.

[padredw]

Just quickly to say: if I could take state legislators on a ride in any pickup towing a fifth wheel over highways in any state I have been in there would be no more concrete highways!