I have an older Semi-Truck, 1990 Volvo, that I use to haul an Auto Transport Trailer. I recently bought an older 5th Wheel Trailer, a 1987 Mallard Prairie Schooner. The name is very apt because it is really a big old boat. My problem is that the King Pin on the trailer is smaller than the 5th Wheel Hitch on my tractor. Changing out the tractors 5th Wheel Hitch is not an option because the Tractor is a working truck. So, my next thought was to change out the King Pin on the trailer. Does anyone know how hard this will be? I bought the trailer in another state and before I left I failed to really look at the King Pin Box to see if it was welded on or bolted on. Would anyone venture a guess as to how it is mounted? To change the pin - would I need to just weld on a new pin - or must I change out the whole Pin Box? I'm neither a welder or a RV'er. This is my first venture into RVing. If I can ever figure out how to fix this problem I think that I'll really enjoy this old boat. My tractor is very capable of hauling the trailer - if I can figure out how to change the King Pin on the trailer. HelP!! I called a Semi-Truck Parts store and they told me they had the Larger King Pins in stock for only $55.00. But, I failed to ask them how they were mounted(bolt on or welded), so I'll have to call them in the morning and find this out. Any advice on this matter would be appreciated.

That surprises me as most king pins are the same size. As an older 5th wheel, it's probably all welded in. The newer 5th wheels have a adjustable king pin box that you could replace. So it looks like a weld job. I'd take it to Camping World and see if they can replace the king pin. Or just a good RV service center.

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Originally posted by MrTruck:
That surprises me as most king pins are the same size.

Sounds like the OP has a class 5 or 6 semi tractor.... While the trailer has a RV type 5th wheel hitch. A competent welding shop will be able to adapt the trailer's hitch to a semi's hitch plate.

The problem I see is the brakes. The semi will have air brakes while the trailer might have an electric brake set up. Likely easily solved with the installation of a eletric brake controller and a separate trailer plug for the play trailer. (vs the work trailer)

Thank you both so much for responding. Yes I have a Big Semi-Truck that I am going to use to haul the 5th Wheel Trailer. I haven't been able to go down and deal with the King Pin Box yet. But will probably attack that problem next week. The 5th Wheel Trailer does have electric brakes and I am planning on the seperate plug to solve that problem.

I've contacted several welding shops where the trailer is currently located - both assured me that it wasn't that difficult a job.

Again, Thanks,
Gayle