# After a Dock Strike Folds the Header, Rebuild the Corner Post With It > An angled hit on a dock bumper bent more than the visible header. Each shortcut skipped during this box truck repair would have surfaced again within a season. Source: https://ocrv.info/blog/dock-strike-header-rebuild-the-corner-post Published 2026-04-26. Category: Before and After Repair Stories. About 6 minutes. An angled dock impact folds the rear header and pushes the corner post out of plumb at the same time, because both meet at the same joint. Straightening the header alone leaves a bent post that cracks the skin at the top corner, and leaves a door opening that never measures square in its track. ## The short answer Squareness is what a roll up door depends on, and a dock strike takes it away in two places at once. A dry freight box truck that backs into a bumper at an angle folds the header above the door opening and levers the rear corner post outward from the same joint. Repairing one and not the other produces an opening that measures fine on one diagonal and wrong on the other. The door will bind in its track from then on, and the skin at the top corner will crack. ## Skip the diagonal check and the door binds for good The tape measure went on before any hand tools did. Corner to corner across the rear opening, both diagonals, then vertical height at both jambs and horizontal width at floor, mid and header. On a square opening those diagonals match closely. On this one they differed by more than half an inch, which is enormous in a track guided door. Had that check not happened, the natural instinct would have been to pull the visible fold out of the header until it looked straight, hang the door, and call it done. A roll up door does not care what looks straight. It cares whether the two vertical tracks are parallel and plumb and the same distance apart top to bottom. When they are not, the roller pins on one side climb the track while the other side lags, the curtain skews, and the door drags harder every cycle. Owners describe that as a door that got heavy. It is not heavy. It is fighting geometry. Diagonals were recorded before disassembly, after straightening, and again after the new components went in. Those three sets of numbers are the actual record of the repair. ## Straighten the header alone and the corner cracks by next season There is a strong pull toward the cheap version of this job: work the header back down, skin over the wrinkle, move on. The header is the visible damage, and on an angled hit it is also the loudest. But the impact arrived at an angle, which means the load did not stop at the header. It carried through the joint into the rear corner post and pushed the post out of plumb along its full height. A plumb bob dropped inside the rear frame showed the top of the post standing outboard of the bottom by a noticeable amount. The post was not creased. It was bowed, and bowed extrusion holds stress. Leave that stress in place and it works against the skin every time the box twists on a driveway or a rough approach. Aluminum skin riveted or bonded to a post that wants to spring back will crack at the top corner, where the post, header and roof rail all meet, and that corner is the hardest spot on the whole truck to seal afterward. Both the header extrusion and the corner post got replaced rather than straightened, which is often the right call on [collision work](/services/collision-and-structural/collision-repair) involving extruded corner sections. A replaced extrusion carries no memory of the hit. ## Leave the rear sill unmeasured and the floor keeps telling on you Underneath the opening, the rear sill ties the two corner posts together and forms the bottom edge the door seals against. It also transfers load from the rear of the box into the crossmembers below the floor. Nobody looks at it after a dock strike because it is behind the bumper and below eye level. On this truck it had taken a set. Measuring across the sill and comparing it to the header width showed the bottom of the opening was narrower on the struck side, and a straightedge laid along the floor found a low spot right at the rear crossmember. Skipping that measurement would have produced a strange outcome: a new header, a new post, correct diagonals at the top, and a door that still refused to seal at the bottom. Worse, the flexing floor at the rear would have kept working the new corner joint loose. The sill got straightened, the affected crossmember checked and corrected, and the floor plywood at the rear refastened into sound structure. Anything involving [frame and chassis straightening](/services/collision-and-structural/frame-straightening) needs to happen before the panels close, not after. ## Rush the post to skin joint and water finds the plywood liner New extrusion meeting old skin is a joint that has to be built, not just fastened. The rear corner of a dry freight body sees direct spray off the tires, standing water at the dock, and pressure washing, and behind that skin sits a plywood or laminate liner that has no tolerance for any of it. The sequence that keeps water out: - Mating surfaces cleaned back to bare, sound material, with old sealant fully removed rather than covered. - Butyl tape laid under the flange where the new skin laps the post, so the fasteners are bedded rather than dry. - Fasteners set to consistent pressure, since an over driven rivet or screw squeezes the butyl out of the joint and leaves a dry spot. - A non sag sealant bead run over the vertical seam after the joint is closed, tooled rather than left as a raw bead. - The top corner treated last, where vertical and horizontal transitions meet and where two sealant types have to overlap correctly. Rush any of that and water tracks in behind the skin, wicks into the edge of the liner, and swells it from the inside. By the time it shows as a stain on the interior, the plywood edge has usually delaminated for a foot or more in both directions. After sealing, the roll up door track got refit to the corrected opening: brackets set to the new post position, tracks measured parallel at three heights, spring tension checked, and the door cycled repeatedly under watch. Skin at the corner went on, and the refinish work carried the color across enough surface to keep the transition from reading as a patch on a flat white [box truck](/vehicles/commercial-trucks/box-truck) side. ## Photographing the corner before it comes to us Pictures taken at the dock, before the truck moves, are worth more than pictures taken later, because the first thing that happens after a strike is that somebody pulls the truck forward and changes what the evidence looks like. Shoot these: the full rear of the box from about fifteen feet back, straight on, so the opening shape is visible. The struck corner from outside at eye level and again from low, looking up along the post. The same corner from inside the box, with a light, showing the liner and the inner face of the post. The header from inside along its length, sighting down it. The bumper and whatever it hit. And the door in its track, partly open, so the skew shows. Add one wide shot showing the truck's position relative to the dock, which tells us the angle of the hit better than any description. Then walk the tape across both diagonals of the opening yourself and write the two numbers down. That set of photos and two measurements is enough for us to have a real conversation when you [ask for a quote](/request-a-quote), whether the truck runs out of Eastvale, works the industrial blocks along Archibald Avenue, or comes over from Chino by way of SR-71. --- OCRV Center. 23281 La Palma Ave, Yorba Linda, CA 92887. (949) 799-3387. info@ocrvcenter.com. Serving Eastvale, California in Riverside County, about 20 miles from the shop. All work is performed in shop at the Yorba Linda facility. No mobile, roadside or on-site service is offered. Scope is body, paint, structural, fiberglass, interior and vehicle systems work. Engine rebuilds, transmission rebuilds, drivetrain work, DOT inspections and emission testing are not performed.