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Flex Air drastically reduces chucking, absorbs road shock, and minimizes bounce. The internal air bag and built-in strut work with the rubberized pivoting head to achieve a dramatically smoother ride. Replaces Lippert 1621 pin boxes.
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Getting there is half the fun, right? Not if you're being bumped, jerked, jammed, and pushed around from the chucking, road shock, and bounce that occurs as you tow your fifth-wheel trailer or RV. And imagine the costly wear and tear on your trailer as it endures that rocky ride.
Put the fun back into your trip and ease the stress on your trailer by replacing your factory pin box with the Curt Flex Air pin box. The internal air bag and built-in shock work together to cushion your ride, improve handling, and limit strain on both your truck and your trailer. But what sets the Flex Air apart from other air ride pin boxes is the addition of a pivoting head. This head, along with its built-in rubber compound, provides additional cushion, absorbs road shock, and reduces chucking for a significantly improved ride.
A heavy-duty rubber compound is built into the head assembly of the Flex Air pin box. This rubber is the first defense against road shock. It helps to absorb the bumps and vibrations experienced when towing a fifth-wheel trailer over rough roads. Standard pin boxes without any type of shock absorption transfer road shock to your trailer, resulting in potential damage to the trailer and an overall bumpy ride. The shock-absorbing rubber inside the Flex Air takes the beating so there's less wear and tear on your trailer or RV and you get a smoother ride.
Because the rubber may not be able to absorb all of the road shock that you experience, the Flex Air also implements air ride technology to virtually eliminate shock. When you encounter uneven terrain on your trip or hit a pothole on the highway, the Flex Air pin box compresses vertically, similar to how a pair of scissor blades closes in on each other. This compression transfers the road shock and vibrations to the internal air bag, saving your fifth-wheel hitch, trailer, and tow vehicle frame from enduring a rocky ride.
A built-in strut, or shock, controls the Flex Air's compression so that the internal air bag doesn't burst. The strut also causes the pin box to appropriately rebound without any bounce, and positions it to be ready for the next bump in the road.
The pivoting head on Flex Air allows for controlled back and forth movement of the king pin to reduce the uncomfortable jarring known as chucking. Unlike a rigid pin box that has little give at the point where the trailer and the hitch are connected, the Flex Air can pivot slightly to compensate for those times that your trailer suddenly pushes or pulls on your tow vehicle. Because the pin box head - not the king pin itself - is moving, the chucking that often occurs when the king pin jerks around inside the hitch is significantly reduced.
Simple Setup and Installation
First, simply remove your existing Lippert 1621 pin box from your trailer. The Flex Air uses the same bolts that held on your original pin box so no additional hardware is required for installation. Plus, the Flex Air pin box comes out of the box ready to be put on your trailer, so no assembly is needed. Because the Flex Air is quite heavy, you should put it on an elevated surface or have a friend help you support its weight during installation.
The internal air bag should be inflated after the Flex Air pin box has been mounted on your trailer. Using the air intake valve, inflate the air bag until the outer cylinder of the shock rises high enough to fully expose the yellow inflation indicator sticker.
Customer Satisfaction Score:
85% were satisfied with this product
15% of customers were not satisfied
Ratings & Reviews
Dennis P.
8/14/2020
Absolutely Wonderful! After a year and over 10,000 miles I could not be happier with this hitch. Easy to hook up and unhook with safety features that allow you to easily see it is hooked properly. Over the past 25 years I have purchased 3 5th wheel hitches and by far this is the top of the line without the top of the line price. Several people have ordered because of seeing our hitch.
Quinton
1/25/2021
Very happy with my pin box. Does not seem to be much difference on the truck, but the inside of the trailer tends to get shook up a lot less.
Unclefester
10/7/2019
Best thing we ever did!
Faith E.
9/9/2019
has trouble keeping air in the 2 rubber doughnuts. seems that it needs top up a couple times a week when travelling. have heard that others have the same issues and have upgraded the rubber doughnuts to the 20K with better success.
Do you have a question about this 5th Wheel Pin Box?
Condition: Installed
Notes: Item has been previously test fitted and has cosmetic scratches from install.
Info for this part was:
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Joel
5/14/2025
I like the Curt Air-Ride pin box and it contributes to a smoother ride, but it has not eliminated the shucking that I had hoped for. Good quality hard installation.