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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.
Features:
Specs:
Notes:
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:
81% were satisfied with this product
19% of customers were not satisfied
Ratings & Reviews
This is an awesome upgrade it takes the chucking away 100% smoother than the standard king pin, the only issue is that after setting at one location for awhile I have to top off the air?
It is definitely a great addition to the HL Landmark
Christina was wonderful - walking me through issues involved with the purchase, and following up throughout the process all the way up to arrival at my door. 5-star customer service by her and etrailer!
replaced original FlexAir pinbox design with this new model. easy swap out and much improved pinbox performance. great service and delivery.
Packaging and delivery was spot on!! Truck backed up and dropped the new king pin right in front of my fifth wheel trailer for install. I'll follow up with more details once its installed.
Smooth out the right of the fifth wheel so well reduce chucking I will never buy another fifth wheel without this hitch
product smooth's out ride over our great highways (cattle paths) here locally. only issue I have is that the pin box once tightened down into the original bolt holes is leaning to one side and is noticeable in the rear view mirror as I haul.
The hitch pin box did exactly what I wanted it to do. It gave me more bed clearance and a better ride for the fifth wheel. The only drawback, is that it touches the side of the bed on sharp turns.
Really nice piece, install was a breeze other than it being really heavy!
It definitely improved the ride of my 45 foot toy hauler but it also raised the front of my unit about 3 inches (with the airbag inflated to 90 psi) and that’s after I lowered my hitch to its lowest setting.
Great product for any fifth wheel! Really smoothes out the ride for both the truck and trailer. Easy bolt on install! All RVs should come with one of these!
Unclefester
10/7/2019
Best thing we ever did!
Definitely a two person job, looks better attached to our momentum than the stock. Only wish the arrow was more visible.
Great product with quick delivery. Does not come with mounting hardware, so if your existing pin box only bolts on with a couple of bolts you will more. Good idea to just order them at same time. Also did not come with glide (lube) plate as listed in info videos.
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.
Well, The hitch was to be delivered on the 23rd. Tforce the company you chose to deliver is located in the Philippines and after speaking to 5 different NON English employees I gave up. So I called the Tforce in Fontana Ca where the hitch is now. NO One answers the phone then after 30+ attempts a female answered and before I could complete my request she transferred my call to an empty line.
Formerly I had a hitch with air bags. Changed trucks with different mount. Looked to replace the easy ride and fell in love with this king pin. Now have several thousand miles and found this king pin better than the shock hitch! I would buy it again if something happened or we changed trailers!!!!!!!! I ordered the longer one and it allows me to let my tail gate down when hitched or hitching. Wonderful.
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.
Driver did a great job dropping off items and putting them off to the side out of the way!
William was very helpful getting the pin box I needed. IT bolted right on the trailer,the pin location is 3" further forward on the trailer and gave me a better ride height. the trailer pulls a lot smoother than before.Thank you e trailer
This is an amazing product. Helped so much with things rattling loose in the 5th wheel. The ride in the truck also vastly improved. Would definitely recommend. ETrailer was also great to work with. I called their office to make sure I was ordering the correct one for our unit and they were super helpful.
The shipment arrived today on time and in great condition. I installed it with two friends in 45 minutes. Lakeia was a great help. She answered all the questions I had. Her response was timely and accurate. I am very pleased with my experience.
The reason I purchased the pin box is I needed some extra distance between my truck bed and 5th wheel. It did the trick, I got an extra 5" (had 4"). But the ride is amazing! Very pleased with towing, I almost can't tell I'm pulling a 44' toy hauler cause it's so smooth. My ordering experience was top notch, I will definitely purchase again from etrailer.com
Believe the hype! This kingpin is the “kingpin of kingpins”. I went from my straight 1621 to this. The difference was astounding. It was like going from being on the SS Minnow on rough seas to the USS Nimitz on a calm bay. Very little chucking. True night and day difference. Yes, it is a little pricey, but if you consider the potential outlay of cash to the incurred maintenance of wear and tear from travel to BOTH the tow vehicle and trailer-I felt it was worth the investment. If you’re looking into upgrading-do it. It’s worth it!
Installed on my 2019 Grand Design Momentum 351 and it fit perfect. Shipper came on time and helped me slide it on to my tailgate, it came on a small pallet. I backed it up to the camper and used a car jack to lift up the aft end. Once I got the lower holes on either side aligned I installed bolts loosely. Then I jacked up the forward side and installed bolts once they lined up. Installed very easy by myself. I did purchase grade 8 replacement bolts from [farm store]. Original bolts were 1 1/2" I put in 2" because the metal is thicker on the new pin box and I wanted threads to come through the nuts. I installed the new bolts with the nut on the outside to make it easier to torque the bolts to the required xxx lbs. I haven't got to try out how it helps out for chucking yet. I will add to this review later to tell how it went.
Easy install. Took 2 people due to the weight of the Flex Air pin box. The Lippert 1621 is pretty light comparatively. We placed the pallets the flex air was shipped on (Estes Freight) in the back of the Dually, then labored the Flex Air on top of the pallets. Backed the truck under the 5th wheel and were able to start getting bolts through with small adjustments. Too heavy to lift and put bolts through. Tools used: 1/2 in High Torque Dewalt Impact, 15/16 impact socket, 15/16 wrench, 50-250 torque wrench, impact driver to get the breakaway removed and remount. The grade 5 bolts I have required xxx ft lbs torque. Completed install in 45 minutes.
I'm sorry I can't give a 5 star rating for this order. As always etrailer service was 5 star. But, unfortunately the pin box was received with some damage. Originally I thought the damage was limited to cosmetic only. There were some gashes in the metal and deep scratches in the paint. However, after about 5 months of use I noticed a bolt on the jaw that appeared to be misaligned. Upon inspection it was obvious that the bold was striped. It must have taken a direct hit when dropped during shipping.
The good news is LCI did replace the pin box for me under warranty. However, I had to pay for the installation which was understandable.
In retrospect I should not have accepted the shipment. I'm not sure where the packaging was done but this would have been avoided if this 230 lb product was packaged appropriately.
The order was delayed while etrailer waited for it to be built after I ordered it. Shipping was slow and the product sat on the truck dock in Denver for at least one day before being transferred to the freight company for delivery to Casper. The local freight company was good to deal with once it finally got Casper and I picked it up on their dock. Removal of the old pin box went smoothly, but there were absolutely no installation instructions for the Curt Flex Air pin box and there were none on the internet. The online video was no help, either. Finally got it installed after too many hours. I DO NOT understand why the new pin box has raised the nose of my 5th wheel by over 2 inches, so now I have to work on the hitch and lower it 2 inches. Will be glad when this is DONE tomorrow.
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.
Kate F.
5/19/2025
My wife and I are very pleased with our purchase of this product. We have taken numerous trips with our rig since installing it and what a difference it has made from the standard basic pin box. We no longer feel any chucking from starting off and stopping when towing our trailer. I figured it would definitely reduce it but it eliminated it completely. We tow with a one ton F350 long bed SRW and a B&W hitch. In my opinion It is not a DIY installation because of the sheer weight of the product otherwise I think that it would be. It is not a complicated item to install its just super heavy. In addition to my praise of this product, I would like to recommend the addition of grade eight hardware to be included with the product for installation. I think a few dollars more for the price should more than cover that cost. When it comes down to it the grade five hardware is sub standard for such a massive object in my opinion. It is supporting not only the weight of the pin box but the torque under load as well so for the purpose of safety, which is why we purchased it in the first place the hardware has to come off anyway to take off the old pin box. So why not replace it at the same time. My two cents worth anyway. I would definitely recommend this product to others who are looking to eliminate the chucking felt under a standard fifth wheel pin box.
This pin box is a beast! I am glad I had a tractor with a front end loader and pallet forks! Shipping was pretty fast and item was received in great condition. I haven't hooked it up on to the truck yet, but I expect it do deliver as advertised. I will know more after our trip at the end of August to Jellystone RV park in Elberta, AL. It certainly looks very nice on our 2017 Sandpiper Select 329RE!
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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.