5th wheel hitch

[Dale_S]

Has anyone installed a 5th wheel hitch in a 3500?
I plan on doing the job in a couple of weeks. Just
wondering if there are any problems I should look out for. Will be towing a 34ft. Mountain Aire.

TIA
Dale

[Big O]

Since I pull some gooseneck trailers, I decided I would convert the 5th wheeler travel trailer to a gooseneck hookup. That way my Una-goose hitch leaves my truck with a flat clean bed, when not being used--no 5th wheel hitch in the way.

[johns]

Talking to my RV dealer last weekend, he told me that one of his techs had always complained what a PITA it was to install the 5er hitch in the GM trucks. Apparently one of the brackets needs to turn in rather than out and it extends over the top of the frame. Have to put the bolt thru before bolting it to the frame. He says you can't get a socket in there and have to tighten with a wrench.

Due to a neck injury I can't do it myself anyway, so he it putting it in for me.

[LarryM]

Big O:

How did you convert your 5th wheel hitch to a gooseneck? I know of several adapters, but they don't seem to work well with all 5'ers.

I don't have an RV yet, but I have been considering just replacing the entire frame in the hitch area when I do get one.

[richp]

Thoughts on two points in this thread.

1) When I had my Reese fifth wheel mounting plates moved from my '93 to my '01 K2500, it seemed that the frame on the new truck was wider than that on the old one. Clearly, the Reese pieces (cute, huh?) were too short. The tech doing the work managed to adapt using some HD brackets. He said that Reese had been slow in developing new mounting plates that were wide enough to span the new GMC frames. Perhaps by now the new Reese plates are available....

2) On the matter of changing from fifth wheel hitches to goosenecks, I had a custom gooseneck adapter made for my Layton hitch on a mid-size fifth wheel RV. However, the amount of additional movement it generated in the hitch head made me abandon the idea and return to a standard kingpin arrangement. When I looked in the mirror I saw motion in the frame that was never there with the fifth wheel hitch. I concluded that sooner or later the frame would fatigue from all the flexing and fail -- not worth the risk to me.

It's easy to visualize now, but in making the conversion I failed to take leverage into account. When you move the actual hitch point from the kingpin (8-10 inches above the bed) to the ball in the bed, you increase the lever arm acting on the hitch head, and therefore the trailer frame. That's OK if your frame is engineered for the increased stress, but I have no way to know that. Actually I expect if you asked the RV manufacturers they would be reluctant to approve anything like this for liability reasons, but I suppose that's an option for getting some engineering input. A commercial conversion to a gooseneck might be safer from the hitch point of view only, but to be sure about the frame I still would want someone who knows more than me to look at the rig and assure me that it's built to handle the additional load.

For what it's worth.

Rich Phillips
Member #28

[Big O]

LarryM,
I have not made the conversion yet, but that is what I decided I would do, instead of installing the clutter of the 5th wheel hitch. During my searching of the products I found several very well made adapter that replace the 5er connector on the trailer. Most cost from $300 to $450.

[Maverick]

I bought an adapter called a "Cody Coupler". It works good and the center of the kingpin is directly above the gooseneck ball so the load is the same on the trailer frame.

Send me an E-mail and I will send you some pics if you like.

[ 03-19-2002: Message edited by: Maverick ]</p>

[richp]

A final cautionary thought on the fifth wheel/gooseneck conversion and then I'm done (we could use input by a real engineer here).

I could be mistaken, but I think leverage can be increased in such applications by modifications in both horizontal and vertical distances. Both vertical and horizontal forces at work, so changes in either dimension will change the loads on the structure. When you change to a gooseneck in the bed, the vertical distance from where the hitch is attached to the frame to the point where the force is exerted (the ball) is increased considerably. Even if the ball hitch point is right over the old kingpin hitch point this has to be a factor to consider.

If you increase the distance between the frame and the point where force is applied in the vertical dimension, then you increase the amount of leverage on the frame also. This might not matter much going down the road, when typical forces are vertical (from road joint bounces and so forth). But think about starting -- and particularly rapid stops. Force is applied not vertically, but horizontally through the vertical gooseneck. And in those instances I can visualize leverage (and the corresponding torque on the frame) to be increased by a factor of 2 or 3 when the longer gooseneck is used. Again, I saw this actually happening in my trailer when I made the conversion and it concerned me enough to go back to the fifth wheel kingpin.

My cautionary thought is that anyone who wants to make this conversion should either get something in writing from the manufacturer of the conversion device or the trailer manufacturer, saying that the engineering has been done as to this specific hitch and trailer, and that it is safe.

For what it's worth.

Rich Phillips
Member #28