Pin Box Upgrade for Grand Design Momentum 350 With Lippert 1621
Updated 04/28/2026 | Published 04/25/2026
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Question:
What pin box upgrade do you recommend for a Grand Design momentum 350 with a Lippert 1621 pin box. I have a BandW Companion sliding hitch installed on my truck. I have been thinking of upgrading to a Flex Air but I no longer see it advertised for sale on Curt website so worried about it being discontinued. TIA
asked by: Steve R
Expert Reply:
Hey Steve! A lot of things have shifted over to the Lippert store since they acquired Curt. They still have the Curt Flex Air listed, and there hasn't been any communication about it being discontinued. This is a great upgrade between the pivoting head, shock, and air bag. You will be really happy with this setup, especially paired with the Companion, definitely recommend it.
The # LC328492 you were looking at is the 18k version. I'm not sure what year your Momentum is but it looks like some of those are right at 18k for the GVWR so the # LC369535 rated for 21,000 lbs is the better option.
Where are you headed once you upgrade your pin box?
(click to enlarge)
Product Page this Question was Asked From
Curt Flex Air 5th Wheel Pin Box - Lippert 1621 - 18,000 lbs
- 5th Wheel Pin Box
- Upgraded Pin Box
- Absorbs Road Shock and Reduces Chucking
- 18000 lbs
- Air Ride Suspension
- Fixed Turret
- Lippert 1621
- CURT
more information >
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on 5th Wheel Pin Box
Steve R.
4/28/2026
My 350M has a GVWR of 16500..