Can You Replace Your 5th Wheel Pin Box With A Higher Capacity One To Triple Tow A Boat Trailer

Question:

Early 2000s Keystone Montana with a Lippert 1621 - 15,500 pin box and factory receiver hitch on the back of it. Wanting to pull a boat behind the camper, but doing my rough math - between max loaded weight of camper and boat - Ill exceed 15,500 by a little bit. Not a bunch, but exceed it none the less. If it were for a little 10 mile jaunt, Id probably chance it - but looking at longer trips and feel like the smart move is to upgrade the pin box to an 18k or 21k. My question revolves around the wings of the pin box... Are the wings all the same? So its just a matter of unbolting the 15.5k pin box and bolting in the the 18k or 21k on the existing wings? Or does it turn into a tear apart - cut out, and weld in the new wings to get the added capacity? Thanks

asked by: Wade

Expert Reply:

Manufacturers recommend only using 80-85% of a pin box's capacity so you would definitely be putting too much of a strain on the pin box if you were to exceed the capacity and would most likely have something fail. Swapping pin boxes is as simple as unbolting the old one and popping in the new one, but there are limitations due to the strength of the trailer's frame. Manufacturer's don't really want you to upgrade because the higher capacity pin boxes weigh more and you're throwing off the balance between the frame and pin box and could end up cracking the frame.

For example, the 15,500lb # LC1191191 weighs 99lbs, while the 21,000lb # LC1387883 weighs 141lbs. It can be a lot of weight hanging off the front of the trailer and the frame may not be capable of handling it.

In your situation you'd most likely be fine, but there is always that potential for something to fail so I'd like to have you as well informed as you can be prior to making any changes.

If you're going to swap out your pin box you might also want to look into cushioned options like the Rota-Flex # LC328330 or Flex-Air # LC328492 to help improve your ride quality. I've attached some videos below that go over both of these options, but I can answer any other questions you might have if you're interested.

Since you're triple towing trailers you'll also need to install a 4-pole wiring harness like # C47NR on the Montana to pass your light signals through to the boat trailer. You can splice the wires directly to the tail lights with some butt connectors # DW05744-5 .