Installing the Flex Air Pin Box on our Fifth Wheel Trailer

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Why A Fancy Pin Box?

Our Keystone Cougar 276RLS trailer came with a basic solid steel pin box. This works well on smooth highways, but things can get a bit jarring when the roads get rough. I find it particularly annoying when we travel through larger cities where the highways have been badly worn down by traffic.

To safely keep up with the flow of traffic slowing down for a rough section is sometimes not an option. Large cracks in the cement roadways and bridges can cause harsh jolts and uncomfortable chucking ( a back and forth jerking or tugging motion).

We also love to boondock routinely dragging our rig down lumpy or wash-boarded dirt and gravel roads in search of those most scenic of camp spots. Our 1 ton Ford F350 dually has pretty stiff rear springs so the sometimes intense vibrations can get very uncomfortable.  I often wonder if damage to the fifth wheels frame might take place!

Boondocking in Quartzsite Arizona

On my upgrades wish list for some time now has been a replacement pin box with built in shock absorption. Therefore, I was super excited when Lippert Components contacted me offering to send out a new Flex Air Pin Box for a good old Love Your RV! Review. With a built-in adjustable airbag, oil filled shock, pivoting head and thick rubber buffer it looks like just the ticket to smoothing out our journeys.

Flex Air Pin Box Photo

Installing the Flex Air Pin Box

Removing the old OEM pin box was dead simple with the right tools. I needed a 15/16th socket, torque wrench, and a large 15/16th wrench. Four nuts and bolts on each side hold the pin box in place. Prior to removing the pin box, I took a measurement from the bottom of the king pin to the ground. The new pin box will be installed as close as possible to the same height so proper truck bed rail clearance and trailer level are maintained.

Tools for Pin Box installation

The biggest challenge in swapping out the old pin box with the new Flex Air is the weight involved. The Flex Air weighs in at a robust 225 lbs. Quite a bit of weight to be trying to hold in place while threading in and tightening the bolts. I was lucking enough to have a hydraulic lift table handy when doing the job. Another thought I had was to use my trucks tailgate to support the weight during install and using the trailer landing jacks to get it in place.

Installing Pin Box with Lift Table

Once the Flex Air Pin Box was installed and the bolts snugged up the next step was to tighten them to the proper torque specification.

Lippert’s pin box install manual states “We recommend using the nuts, bolts and washers that came on the coach unless they are in bad condition. Make sure replacement fasteners are the same grade and diameter as those removed for torque specifications on pin box bolts refer to manufacture’s specifications. If no torque requirements exist, torque 1/2” bolts a minimum of 110 ft/lb and torque 5/8” bolts a minimum of 160 ft/lb and torque 3/4” bolts a minimum of 210 ft/lb.

I reused the OEM 5/8th bolts, nuts, washers as they were all in excellent shape and tightened them up to 160 lbs. I did have to move the new pin box up one alignment hole to have the king pin at the same height as my old one.

*UPDATE* – I decide to replace the original Grade 5 bolts with Grade 8 bolts. I learned that Grade 5 bolt max torque is 150lbs where the same size bolt Grade 8 is over 200 lbs. Also, I’ve reversed them with the nuts on the outside. I was advised that they should be torqued on the nut rather than the bolt head. It was too difficult to fit the torque wrench inside the pin box to get at the front bolts.

Upgrade from Grade 5 to Grade 8 bolts

The final tasks were to remount the emergency trailer breakaway brake switch (it had been bolted onto the original pin box). Then add air to the new Flex Air Pin Box’s air bag. It gets inflated until a factory marked line is visible on the shock absorber. Now it’s ready to take out for a test run and a recheck of the bolt torque after 25 miles or so.

Video of My Flex Air Pin Box Installation

Stay Tuned For the Full Review

My wife and I are departing in a few days for our annual journey south. We travel from our summer home on Vancouver Island all the way to southern California to begin our meanderings in the South West desert regions. Along the way, we will encounter many road conditions that will test the new Flex Air Pin Box starting with the loading and unloading ramps of the Port Angeles Black Ball Ferry.

Enjoying the Oregon Coast

Then we travel the curvy and sometimes lumpy Highway 101 down the Oregon Coast. But the real test will be the highways through California’s Central Valley like Interstate 5 and Highway 99. Due to the tremendous amount of truck traffic along these routes the roadways and bridges are often beaten up. Potholes, large cracks and long sections of under construction zones are a normal occurrence.

Central Valley California Highways

Once we are in SoCal I’ll put out a full review of the Flex Air including some video footage of it in action along the way. I’m expecting this new pin box to dramatically smooth out our ride.

Update – the Flex Air didn’t work out for my rig. See why and which other Lippert Pin Box worked perfect.

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Flex Air Pin Box Installation by Love Your RV! blog - #fifthwheel #RVupgrades


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