Hi All I have a 1981 Kenworth W900 ,heavy spec,with a 16 ft Langfab aluminum box.12 yds approx. All in reasonable shape. Question is this. I noticed after I got truck last year that,empty,the beams under box did not come to rest on truck frame at front. About half an inch gap.Loadsed everything sits in place. Sighting down the beams I can see they have a very slight sag.. I added some 1/4 inch shims to top of frame ,doubled up at very front,to ensure better load distribution? Is this slight sag a normal thing with age or?Nothing seems to be cracked or broken although there have been some repairs welded up over the years.
I have seen quite a few steel beds get warped over time not any more than what you described Not sure on aluminum have not been around that many there was one aluminum end dump I seen get a slight bow in it from the ram not being down completely when they dumped the bucket in it made the bed bow about a half inch guy that owned paid no mind to it If it was getting worse the box would show signs of a crack around the corners or in the middle of the top rack of the bed
Around here is generally the Asphalt haulers that warp really bad, combination of heat and length of time with partial load in a up position feeding a spreader box does it.
So I'm guessing this is nothing to break out in a rash over....sounds like it might be a normal thing for an old truck?how much sag would those asphalt trucks get Miller?
Would see it bad enough over a few years to require the box coming off and replacing the floor runner rails. A few times one Quarry would take their old trucks scrap the boxes out buy new. Can see no issue if the upper structure is not bowing out where becomes a nuisance or indicates is trying to fold out. Shim for now and watch.
A lot of times, boxes that haul a lot of rock get the sides pushed out, which in turn bows the box.
Shot rock especially.