Box Truck U-Bolts Working Loose - Will Lock Washers Help?

[D60]

Yes, I tested that out. Bought some Hillman Grade 8 split lock washers and they flattened out at less than 15 ft lbs. Stacked eight of them and the stack flattened out at about 50 ft lbs, before my desired torque of 60 ft lbs.

Gave up on the lock washers and just used flat washers. I applied anti seize so that I can retighten as necessary for a few years until it seizes in place from rust. Planning on checking torque every six months.
View attachment 250270

If that's just flat bar at top of photo, it's almost surely deflecting. Go thicker/wider, or ideally have some brakes to add rigidity. Look at leaf spring plates, esp where the plate is on top of the springs

 

[George7941]

I am following industry standard practices.. 5/8 in Ubolts, 5/8 in flat stock for tie plates. The shop that supplies me with these items ( they do a lot of box mounts) told me the plates will bend and that is when you stop tightening..

I am going to see if periodic checking of torque will keep them nice and tight.

 

[D60]

I am following industry standard practices.. 5/8 in Ubolts, 5/8 in flat stock for tie plates. The shop that supplies me with these items ( they do a lot of box mounts) told me the plates will bend and that is when you stop tightening..

I am going to see if periodic checking of torque will keep them nice and tight.

Ok you're following standard practices and getting unsatisfactory results. Nonetheless, sounds like you got it all figured out. Glad to hear it's been resolved!