RV frame cracks and weld failures: How to check yours
A trailer frame cracks where the load concentrates: at the spring hangers over the axles, and at the front overhang where a fifth wheel's pin box meets the frame. The frame maker publishes the repair procedure, and the trailer maker publishes a measurement for how far that front deck moves under load.
By OriginRV. Last reviewed on Nov 2, 2026.
Where a trailer frame cracks
A trailer frame is two steel I-beams running the length of the coach, tied together by cross members, with outriggers carrying the floor and spring hangers carrying the axles. Lippert provides frames for multiple trailer manufacturers, and the failures that get reported cluster in two places.
The first is the axle area. The spring hangers are welded to the bottom flange of the I-beam, and that joint is where the road's load enters the frame. Lippert's frames support page carries a repair procedure for frame cracks, which is the plainest sign that they are a known failure point rather than a freak one.
The second is the front overhang of a fifth wheel, where the pin box bolts to the frame and the weight of the trailer hangs from that joint. Complaints filed with the National Highway Traffic Safety Administration describe cracks there, and describe the exterior fiberglass cracking above them as the visible symptom.
Frame flex, and the number the makers put on it
Some movement in a fifth wheel's front deck is normal, and Grand Design says so. What matters is how much. Grand Design's technical service bulletin defines the concern as movement greater than 3/8 inch, measured with the weight on the landing gear and again with the weight off, and that is the figure NHTSA's investigation quotes.
The measurement takes two people, a tape measure and a tripod, and the bulletin's steps are these. Put the trailer on a stable, level surface and lower the front landing gear until it is free of the tow vehicle and fully supported by the gear. Leave the rear stabilizer jacks up. Mark one fixed point on the lower corner of each pin box side plate and one on the bottom of the main I-beam. With the weight on the landing gear, measure between the marks on both sides and write the numbers down. Then raise the front and support the kingpin with a weight-rated tripod, retracting the landing gear until the pads are a quarter to a half inch off the ground, and measure both sides again. Subtract the weight-on numbers from the weight-off numbers. A difference of more than 3/8 inch is the point where the bulletin says to contact Grand Design before anything else is done.
The number only means something if the reference points do not move, which is why the bulletin has you mark them rather than measure to a feature of the frame. It also notes that weight in the front storage compartments changes the reading, so empty them before taking a measurement that comes back close to the limit.
What the investigation says, and what it does not
In October 2024 NHTSA opened a Preliminary Evaluation into frame flex on 2017 to 2023 Grand Design Momentum and Solitude fifth wheels, a population of 55,887 trailers. The resume records 23 complaints. Twenty-two of them allege that frame flex let a cargo or entry door open while the trailer was moving, some with objects lost on the road, and six also allege that a slide-out extended partway. One injury is recorded. The agency's stated concern is that doors opening and slide-outs extending in transit increase the risk of a crash.
The same document records where the two companies stand. Grand Design's position is that some flex is normal, that it happens in the upper deck area, and that its effects are cosmetic: moving sidewalls, damaged cabinets, binding doors. Lippert's position is that the effects can reach back as far as the front axle. Neither is a finding.
A Preliminary Evaluation is the first stage of a defect investigation. It is not a determination that a defect exists, and it is not a recall.
How to check yours
The measurement tells you how much the front deck moves. A visual inspection tells you whether the steel has already cracked.
The cracks in the NHTSA file are in the rail above the spring hangers and at the cross members, so those are the places to start, along with the length of both I-beams, the outriggers, and the pin box area on a fifth wheel. A crack in painted steel bleeds rust along its own line, which is what makes it visible at all, and the flange is easier to read than the web because it is the surface you can see without a mirror.
The body gives you the other half of the picture. The complaints describe trim separating from the siding, exterior fiberglass cracking, doors that bind or open in transit, and slide-outs that creep out. Any of those on a trailer is a reason to look at the frame rather than at the trim.
How much load the frame carries is set by how the trailer is packed and hitched, and the weight calculator works out tongue and pin weight and payload against the truck's ratings.
What a repair involves
Welding, and the procedure belongs to the frame. Lippert's frames support page carries the procedure for repairing cracks with a reinforcement angle and a V brace, and the frame carries an identification tag that says which frame you have; Lippert publishes a guide to finding that tag. The procedure is written for a specific frame and a specific crack location, so the first step is to identify the frame rather than to find a welder.
The route is to photograph the crack, identify the frame from its tag, ask Lippert for the repair procedure for that chassis, and hand the procedure to a welder for an estimate. A welder working without the procedure is guessing at how much reinforcement the frame needs.
Where the measurement is inside the 3/8 inch limit, Grand Design's bulletin has a different repair: replace the existing lags in the main rail, add half-inch lag bolts to the holes that are accessible, bed the threads in epoxy, and cap-seal the attachments. That is a repair for movement, not for a crack.
What this costs
The bulletin carries a flat rate of six hours for the flex inspection and the lag work, which is the maker's time allowance for that job. A crack repair is welding labor on top of it, and what drives the price is access. The underbelly covers the frame, so it has to come down before the top of the rail and the far side of a crack can be reached.
Related guides
A cracked frame often shows up first as a crack in the wall, and delamination covers what a wall crack means and what the makers document about repairing one. Overloading is one of the ways a frame gets there, and towing capacity works out what a trailer can actually carry. The axle area is where the frame and the running gear meet, and tire replacement covers the wear patterns that point at an alignment or suspension fault. Water reaching a slide-out floor is the other slow structural failure, and that is slide-out leaking.
Sources
- NHTSA Office of Defects Investigation, resume for PE24029, for the scope of the frame flex investigation, the population of 55,887 trailers, the complaint counts and what they allege, both manufacturers' positions, and the 3/8 inch threshold.
- Grand Design, frame flex inspection bulletin, for the measurement procedure, the instruction not to lower the rear stabilizer jacks, the 3/8 inch limit, and the lag repair for a measurement inside it.
- NHTSA, search safety issues, where the owner complaints behind the investigation are filed, including the reports describing cracked welds at the pin box, exterior fiberglass cracking, and cross members broken off the I-beam.
- Lippert, frames support page, for the repair procedure for cracks repaired with a reinforcement angle and a V brace, and the frame identification tag guide.
- Lippert, repairing frame cracks with reinforcement angle and V brace, for the repair method itself.
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