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  1. Fifth Wheel King Pin
  2. CURT
  3. Lippert 1621
  4. 18000 lbs GTW
  5. Upgraded Pin Box
  6. Absorbs Road Shock and Reduces Chucking
Curt Flex Air 5th Wheel Pin Box - Lippert 1621 - 18,000 lbs

Curt Flex Air 5th Wheel Pin Box - Lippert 1621 - 18,000 lbs

Item # LC328492
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Retail:$2,034.30
Our Price: $1,368.66
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Fifth Wheel King Pin
This item qualifies for Free Truck Freight Shipping
Shipping Weight: 232 lbs
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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. Call 800-298-1624 to order CURT fifth wheel king pin part number LC328492 or order online at etrailer.com. Free expert support on all CURT products. Guaranteed Lowest Price and Fastest Shipping for Curt Flex Air 5th Wheel Pin Box - Lippert 1621 - 18,000 lbs. Fifth Wheel King Pin reviews from real customers.
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  • Reviews (97)
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CURT Fifth Wheel King Pin - LC328492

  • Lippert 1621
  • 18000 lbs GTW
  • Upgraded Pin Box
  • Absorbs Road Shock and Reduces Chucking
  • CURT
  • Fixed Turret

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:

  • Air ride pin box with a pivoting head replaces standard pin box on your 5th-wheel trailer to cushion your ride, improve handling, and limit strain on truck and trailer
    • Drastically reduces chucking
    • Virtually eliminates bounce and jarring
  • Internal air bag absorbs road shock
    • Scissor-like motion allows pin box to compress, compensating for jarring and bounce
    • Built-in shock ensures that pin box rebounds - keeps air bag from breaking down
  • Pivoting head limits chucking by allowing controlled movement of the king pin within your hitch
  • Rubber compound built into the head absorbs road shock
    • Reduces wear and tear on trailer
  • Black powder coat provides rust resistance
  • Sturdy steel construction
  • King pin connects to any 5th-wheel trailer hitch
  • Bolt-on installation with no assembly required
  • Made in the USA


Specs:

  • Designed to replace Lippert 1621 5th-wheel pin box
  • Weight capacity: 18,000 lbs
  • 1-Year limited warranty


Notes:

  • Do not use the Curt Flex Air pin box with any type of gooseneck adapter.

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.


Rubber Compound and Internal Air Bag Absorb Road Shock

Curt Flex Air pin box has a rubberized pivoting head

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.


Curt Flex Air pin box has a shock and air bag

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.


Pivoting Head Reduces Chucking

Lippert Flex Air pin box has a pivoting head that reduces chucking

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.



328492 Curt Flexair Fifth Wheel Kingpin Box for Lippert 1621

Replaces 328492 Lippert Components (LCI) Flexair by Trail Air Fifth Wheel Kingpin Box for Lippert 1621

Installation Details LC328492 Installation instructions




Customer Reviews

Curt Flex Air 5th Wheel Pin Box - Lippert 1621 - 18,000 lbs - LC328492

Average Customer Rating:  4.6 out of 5 stars   (97 Customer Reviews)

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.

- LC328492
by:

This is the best money I have spent on my camper hands down. My hitch weight is a bit over 3200 lbs. I use a PullRite Super Lite hitch, photo attached. Once locked on the king pin, four bolts are set from the adapter plate against the king pin plate. The plate on the Flex Air is twice as thick as the original pin box and I have way more confidence in a solid set of these four bolts. I was blown away by how this hitch absorbed road shock. I will never have another 5th wheel without this set up.


Comments
Since this original post I have gone back to a regular style 5th wheel hitch new truck with factory puck system but the Flex Air is still doing its thing and I will never pull a trailer without it unless something better is invented.
Russ - 02/11/2021


- LC328492
by:

I bought the Flex Air to replace the standard Lippert pin box on our Cedar Creek fifth wheel that weighs 12K lbs. Just looking for something to smooth out the ride and the Flex Air seemed to have good reviews and recommendations. I went to the Lippert website to download the installation instructions because I couldn't get the link on the etrailer website to work. The instructions will give you the torque values required for installation and the air pressure for the inflatable airbag on the hitch. Installation was straight forward, but you better have a plan because this thing is heavy (300 lbs) and it will take some manpower to move around and install.


Comments
Really glad we switched out pin boxes, the Flex Air was a great choice and definitely smoothed out the ride.
Joel - 02/13/2021

Comments
Really glad we switched out pin boxes, the Flex Air was a great choice and definitely smoothed out the ride.
Joel - 02/13/2021


- LC328492
by:

Product arrived in a timely fashion in an un damage condition. Quality was better than expected. Installation for me took about two hrs, with my wife helping. I placed the pin box in the bed of my truck with the help of a frontend loader and let it down on a floor jack. From there install was fairly easy. Pros: Good quality Heavy Duty Cons: You will need 3 or 4 strong friends to handle it No instructions included I did find a pdf on the bottom of the page however that listed the torque for 1/2" bolts


Comments
Works great after a year of use preforms well. I haven’t had to put air after the initial start up.
Paul` - 08/28/2021


- LC328492
by:

Reflection 320MKS Dealing with etrailer was very easy. Starting with getting the correct information on which pin box would be suitable for our trailer. The unit arrived in 10 days from ordering it. Which was less than the estimated timeframe when placing the order. The only down side, on inspection when arrived, the air bag valve was damaged in transit. A quick email with photos, a call to etrailer & they have a replacement part ready to dispatch. Great customer service & i would definitely recommend them.



- LC328492
by:

The FlexAir pin box has been great. The ride while pulling our Laredo 5th wheel is much smoother. Traveling is much more pleasurable. I especially appreciate the follow up from etrailer.



- LC328492
by:

Dealing with you guys and your suppliers ment all kinds of information going in different directions and nothing ever jiving. Worst experience I've ever had with your delivery companies. Making promises never fulfilling them never calling ahead of time me having to chase them down when you chase him down you talk to somebody that is in the orient. They say will have someone call you in 1 hour. Never did they ever call back. I'll just stop is here because I don't want to get angry it's too upsetting. Finally got delivery 5 days after it was supposed to be here 3 days waiting all day long as promised and nobody showed up when you call back they say will have someone call you in an hour. They still have not called driver showed up here finally 5 days late said he didn't have my number you're the reason I know that it would be was here cuz he had a 40 ft tractor trailer



- LC328492
by:

4 stars as I have just recently installed this although I received it over a year ago. I just put 750 miles on it and experienced almost every PAVED road condition imaginable and it worked great. I can't imagine what that would have been like with the stock pin box. 4 stars because I still need to see how it performs off road and I am just a few days into using it on a trip covering OR, ID, MT and WY so I still have my personal evaluation to complete and need more drive time to see if anything fails on it. Installation was a breeze but it's a heavy hitch so caution is advised.


Comments
I just finished a 3,000 mile trip from Oregon to South Dakota. The hitch works like a dream. Very few road issues are transferred to my truck from the trailer. This is a great hitch. Totally satisfied with this purchase.If anything I wish they made an offset pin box so that I could adjust it to make my trailer ride correctly, as it is with my 4x4 it runs a tad nose high.
Arman K - 10/08/2019



- LC328492
by:

Awesome price! Being installed on a Grand Design 375RES. Shipment went great this is a heavy unit, arrived banded on pallets in excellent condition. Installation was simple and as instructions stated. Waiting for the next road trip to be able to test effectiveness. Always been a pleasure dealing with E-Trailer.



- LC328492
by:

Love it! Makes the ride so much better and safer especially when you cross those roller-coaster bridges that will nearly bounce the rear tires off the ground without this hitch. Only complaint is that I have to add air if it sets for a couple weeks.



- LC328492
by:

Install went pretty smooth. Did it from the bed of the truck, using a motorcycle jack in front and a small hydraulic in back. Make sure your torque wrench can dial to 160 ftlbs. I will update after I tow it!!!


Comments
I cannot believe it has been a year....and a trip to Perdido Key, FL and Breckenrigde CO. In addition to taking care of us, I have to tell you, it will take care of your trailer too! Improved our towing experience old pin box was an upgrade Rotoflex greatly. Worth every penny! If you did not see my earlier post, my friend and I installed it ourselves. Motorcycle jack in the back of a pick up bed. :
James J - 02/05/2020



- LC328492
by:

First, about etrailer. As always, their service was outstanding. They honored their low price guarantee without question and shipping was fast. I upgraded from a Trailair Air Ride pin box with a fixed turret. That pin box helped with bouncing and jarring, but I still got a lot of "chucking". This FlexAir pin box solved that problem as well. Installation was a breeze, although you must make sure you have enough adjustment on your trailer to mount this pin box higher up than your existing pin box. I had to mount it at the very highest set of holes on my trailer. Lipperts web site has specs on this pin box and installation instructions, including measurements and torque specs. With the help of a friend and using the bed of my pickup truck, we unbolted the old one and bolted the new one in. Took about an hour and that was not hurrying. I took the trailer out this past weekend with the new pin box and hit some pretty bad roads. Wow! What a difference this pin box makes. I can only describe the ride one way. Smooooooth. I am very pleased with both etrailer and this product. It's pricey, but to me, pulling a large fifth wheel trailer, it's worth every penny. Highly recommended.



- LC328492
by:

I will be on the third flexair pin box when it gets here on the 21st of November 2016. The problem iIm having is with the lower roto flex portion. The rubber block shifts and I have talked to others with the same problem. Lippert has been great about the replacement, But the the hassle of replacing this three times in one year is not worth it.



- LC328492
by:

Have not had a chance to take it for a road test yet. But it fit well, was easy to mount, the issue I ran into was getting the pin height. As my truck is 4x4, and the B&W hitch is as low as it can go, I still needed another 2 inches to get the pin box high enough, could not raise pin box any higher, and with the 5th wheel already at 13'4" did not want to lift the trailer, so ended up lowering the truck 2 inches to get everything back level again. But will find out next week how it works as we start out on a close to 12,000 mile trip to the west coast and back across through canada and back to florida.



- LC328492
by:

I have used my Flex Air for over one year and put around 3000 miles on it. I purchased this for one reason to reduce bucking when I it bumps in the road. I can safely say that it has virtually eliminated the bucking. It has also made the ride a lot smoother. I would highly recommend the Flex air. I did my own install of this product by my self. My rig 2018 Toyota Tundra with a Husky 16 KW Hitch 2017 KZ Durango 30 ft.



- LC328492
by:

Excellent product although we haven;t yet installed it due to the manufacturer torquing the mounting bolts on our original pin box so tightly that I can't get them off. That is no knock on this product. I will be taking it to a dealer for mounting. I will followup for more comments when it's mounted next week. Looking forward to the promised smoother ride. The product arrived quickly and in good condition.


Comments
Fantastic King Pin. It has made a huge difference in our comfort and reduced driver fatigue when pulling the 5th wheel. Nearly no chucking except when bad drivers cut us off forcing a hard break and no porposing of the trailer and truck. Sometimes the ride is so smooth we forget we have a very heavy 5th wheel back there.
Eric - 03/23/2021


- LC328492
by:

This 250 lb item was shipped in a cardboard box that was just sitting on a pallet. When I opened the box I found the Flex Air was sitting upside down with the foam pad on top. I have no idea how the air filling nozzle wasn't damaged. Luck I guess. There were no "UP" markings on the box. No instructions were included. Installation went smooth, it's just heavy so be careful. Instructions and videos can be found on-line. The Flex Air is at least 4" taller than the OEM box that came with our Grand Design Reflection. I mounted the Flex Air as high as I could and lowered the receiver on the truck. The trailer is still nose high but seems to tow fine. My test ride was noticeably smoother. You can see a lot of motion on the Flex Air that would have otherwise been transferred to the truck.


Comments
Fifth Wheel tows smooth. After 5000 miles from Minnesota to the south east US. Freeway and bumpy back roads. Wind gusts up to 25 mph. The trailer tows smooth. No chucking. The trailer is still higher in the front but it has no noticeable effect on towing and the leaf spring suspension can handle it. The tires seem to be equally loaded, no uneven wear.
Steve t - 11/04/2020


- LC328492
by:

Smooth ride and no chucking at all. Great pin box!



- LC328492
by:

This is our second Flex Air. It really smooths out the ride for the 5th wheel on wavy or bumpy roads.


Comments
Covid slowed us down, but it still is smooooth.
Alfred R - 11/07/2020


- LC328492
by:

Very please with this product. It definitely improves the comfort of pulling our 5th Wheel.



- LC328492
by:

Really helped take away most of the jerky ride we used to get from our solid king pin. The air bag helps to smooths out rough roads. As per the advice of Lippert customer service I made 5 pound adjustments until I found the best ride. I keep a portable battery operated air pump along for adjustments. My airbag had a small air leak at the valve threads when new. After resealing the threads all is good.


Comments
Still working great. The smooth ride makes towing much more enjoyable.
Wesley - 05/28/2019



- LC328492
by:

Great product! Took 80% of the bucking out of the ride.It was an easy install and very happy with the results. Just came back from a 4,000 mile test drive and all is good.



- LC328492
by:

In a word, my experience with the Flex Air has been so-so. I bought this product to eliminate a pretty severe chucking problem with my 5th wheel. While this has been a nice improvement, it did not eliminate as much of the chucking as I has hoped. Certainly not to the extent that you see on the e-trailer video for this product, where the bobble head on the dashboard shows almost zero chucking after FlexAir is installed. And yes, I do have a level ride, good weight distribution, and the hitch installed directly over the rear axle. So the typical causes of chucking have been addressed. The shocks do control the up and down motion pretty well, but the FlexAir doesn't do as good a job on the front to rear motion as advertised. Not sure this is really worth the expensive price that is charged for the unit.



- LC328492
by:

Having not pulled a fifth wheel with a traditional pin box setup I have nothing to compare it to. Watching the suspension action over various road conditions I would have to assume that it is doing a very good job of stopping the transfer to the trailer. We have found that we have to keep an eye on the air pressure because it seems to lose air over time (months). We keep a portable air pump in the trailer to cover this situation. The only other observation I have is that the design does seem to carry the nose of the trailer a bit higher. My truck has had no suspension adjustments made to it and the hitch-head is set at it's lowest setting. I can't blame the pinbox alone because there are many contributing factors, but an element of consideration none-the-less. All in all it's a sturdy, well built, piece of hardware that adds a third layer of suspension to the traveling experience. The health of the trailer will definitely benefit from its use. I have had multiple comments made by other campers.



- LC328492
by:

The Flex Air does exactly what I wanted it to do. It absorbs the shock of bumps and transfers that energy to the hitch, not the truck or the fifth wheel. Installation was straight forward with a little bit of planning. It did require I adjust the fifth wheel hitch in my truck as this is a little longer than the original and extends downward more. I was able to modify the settings on my hitch to accommodate. Overall, I've happy I added this to my RV.



- LC328492
by:

Easy install and definitely a beefy king pin.


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    If you are looking for an improvement in ride quality over the Roto Flex you have installed on your trailer currently the best solution is the Flex Air as it cushions vertically and horizontally and the Trailair is just vertically. So for that you'd want the part # LC328492 for an 18k capacity pin box or the part # LC369535 for a 21k capacity version. The standard Trailair isn't a bad choice but if you are wanting the best option the Flex Air is the way to go. The Flex Air is also compatible...
    view full answer...
  • Is Flex Air Pin Box Compatible with Curt Q20 Fifth Wheel Hitch
    The Curt Q20 Fifth Wheel Hitch, # C16130, is compatible with a TrailAir Flex Air pin box as well as other air ride pin boxes. It is not compatible with Sidewinder or Revolution pin boxes because they do not pivot at the fifth wheel hitch. Instead they pivot using a turret at the opposite end of the pin box.
    view full answer...
  • Heavier-Duty Replacement Pin Box For 2013 keystone Alpine 3535e Fifth Wheel Trailer
    We do offer several pin boxes that have more weight capacity than the 16,000-lb you said you have on your Keystone. The first thing we need to know is what model pin box will fit your trailer. Since you said you have a Trailair installed, you can let me know what model it is and I will be happy to find a replacement that has more capacity. That way we will match the mounting bolt pattern for your trailer. Most of the time it is found on the driver side of the pin box on a plate or sticker....
    view full answer...
  • Pin Box Upgrade Recommendation for New 2022 5th Wheel RV With 1116 Pin Box
    I recommend upgrading to a Reese 5th Airborne Premium pin box because it uses and air bag and a shock absorber to give you the best towing experience. The 5th Airborne that fits the 1116 pin box configuration you have is part # 5AB-S500-700 so that's what you'll want to go with. Attached is a link to a video of us taking the 5th Airborne on our test course for you to check out.
    view full answer...


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123. . .16



Do you have a question about this Fifth Wheel King Pin?


Used Items Available
Used Picture for Curt Flex Air 5th Wheel Pin Box - Lippert 1621 - 18,000 lbs
Used Picture for Curt Flex Air 5th Wheel Pin Box - Lippert 1621 - 18,000 lbs
Used Picture for Curt Flex Air 5th Wheel Pin Box - Lippert 1621 - 18,000 lbs
Used Picture for Curt Flex Air 5th Wheel Pin Box - Lippert 1621 - 18,000 lbs
Used Picture for Curt Flex Air 5th Wheel Pin Box - Lippert 1621 - 18,000 lbs
Used Picture for Curt Flex Air 5th Wheel Pin Box - Lippert 1621 - 18,000 lbs
Used Picture for Curt Flex Air 5th Wheel Pin Box - Lippert 1621 - 18,000 lbs
Used Picture for Curt Flex Air 5th Wheel Pin Box - Lippert 1621 - 18,000 lbs
Used Picture for Curt Flex Air 5th Wheel Pin Box - Lippert 1621 - 18,000 lbs
Used Picture for Curt Flex Air 5th Wheel Pin Box - Lippert 1621 - 18,000 lbs
Used Picture for Curt Flex Air 5th Wheel Pin Box - Lippert 1621 - 18,000 lbs
Used Picture for Curt Flex Air 5th Wheel Pin Box - Lippert 1621 - 18,000 lbs
Used Picture for Curt Flex Air 5th Wheel Pin Box - Lippert 1621 - 18,000 lbs

Condition: Surface Scratches

Notes: Item has minor cosmetic surface scratches as well as sticker residue around the frame. Otherwise new and unused.

Our Price: $1,282.06
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