A Rota-Flex pin box uses a pivoting head and a built-in rubber compound to soften the ride between your truck and trailer. It cuts down on chucking, the back-and-forth jerk you feel at stops and on rough pavement, and it absorbs road shock. That design works well on its own, but pairing it with a fifth-wheel hitch changes how the rubber block behaves. Here is what to know, and the two parts PullRite makes to keep things in line.
What a Rota-Flex Pin Box Does
The pivoting head lets the kingpin move slightly instead of fighting every bump rigidly. The rubber compound inside takes the hit when the road gets choppy or when you roll on and off the throttle. The result is a smoother, quieter tow with less of the harsh jolt that wears on you over a long day behind the wheel.
The Problem It Can Cause With a SuperLite Hitch
When a Rota-Flex pin box is towed with a SuperLite hitch, the rubber block inside the pin box can shift out of position during towing. Once that block moves, it no longer sits where it was meant to, and the pin box stops working the way it should. This is a known issue, and PullRite makes a part to handle it both ways: before it happens, or after it already has.
The Rota-Flex Pin Box Rubber Isolator
The Rota-Flex Pin Box Rubber Isolator secures the rubber block and holds it in position so it cannot slip during towing. There are two part numbers, and which one you need depends on whether the block has already moved.
Part #4447 — Prevent It Before You Tow
Use Part #4447 as a proactive step. Install it before you start towing and it keeps the rubber block locked in place from the first mile, so the block never gets the chance to wander.
Part #4446 — Fix a Block That Has Already Slipped
If the rubber block has already begun to slip, use Part #4446. It moves the block back where it belongs and holds it there. This is the corrective part for a pin box that is already out of position.
Each Isolator Is Sold Separately
Each Rota-Flex King Pin Box Isolator is sold on its own. Order Part #4447 if you are getting ahead of the problem, or Part #4446 if you need to correct a block that has already shifted.
A Word on Rotational Kingpin Boxes
Rotational kingpin boxes are popular for the smoother ride they promise, but the rotation they add can introduce trailer sway into fifth-wheel towing. Sway is the side-to-side movement that makes a trailer feel loose behind you, and it is worth understanding before you decide a rotational pin box is the right setup for how you tow.