Solution for Reducing Chucking on Trailer with Flex Air Pin Box

Question:

We purchased and had installed the above Flex Air pinbox #. The old pinbox was a 1621 and our camper GVWR is 14,220. Trailer TRA / REM 349 RLDS-5-Fifth WheelFD-306 Rev A, and VIN / NIV 5L4ER352051007343. Or towing vehicle is a Dodge dully 3500 and has new high quality shocks and Michelin tires. The receiver in the truck, mounted over the axle, is a Reese, model of which I dont know. The camper is an Open Road by Pilgram and is ten years old. Nothing has ever been upgraded or changed on the axle system. The problem is my expectation of the Flex Air has been crushed because my husband and I expected of the Trail Air a great damping of chucking motion when crossing, especially road and bridge joints. Even going down an undulating or wavey road, on the larger waves my fanny was lifted out of my seat. At one point, at one of the bridge joints the action of the Flex Air was so severe with chucking I became a little frightened. I have every understanding there is nothing that will eliminate all chucking, but I dont expect my fanny to raise off the seat. We have talked to two Lippert technicians and have not gotten adequate and/or limited help as to which new pinbox is correct. I would like to talk to an experienced design engineer or technician. we have been told a long bed truck, which we have, needs a medium lenght pinbox, and a short bed truck needs a longer pinbox. Thank you for your response.

asked by: Dianne W

Expert Reply:

For your Lippert 1621 pin box the Flex Air part # LC328492 that you referenced is the correct pin box to use. But that being said the best way to eliminate chucking is with a fifth wheel hitch that has a tight king pin-to-jaw contact. Most of the chucking you feel is the hitch allowing the king pin to move around in the head of the hitch. Going with a hitch that provides a tight connection will get rid of the chucking.

The Reese M5 Hitch part # RP30928 uses a large hook to wrap around the king pin and hold it tight to eliminate the movement and reduce chucking. I am sure you aren't exactly excited to spend more money, but if you have an older Reese hitch I am betting it's one that uses a slide bar jaw design which is notorious for allowing movement. The M5 would greatly reduce the chucking.

expert reply by: Jameson C