Very interesting where it broke: right at the collar thing where it attaches to the lower parts of the suspension. I wonder if there's some kind of stress riser there. I also wonder what kind of range of motion your rear suspension has. On my car, it's pretty well constrained to the vertical axis of the shock, so, in theory, the shock shouldn't break like this. If that's the case with your car as well, you may want to examine your rear suspension more closely to see if it has undue movement in other directions. Perhaps worn bushings or even damaged suspension components?

Ground Control also don't like having threads cut into the shock body for height adjustment, because that introduces stress risers from the threads. Instead they have a cup that goes over the shock body that has the adjustment threads.

Did you look at the break? Was it shiny or dirty? If it's shiny, then it broke off suddenly. If it's dirty, it broke off slowly, maybe over weeks or months as the crack propogates around the circumference. I'm guessing the latter. What brand are the shocks?

Oh, I'm pretty sure the break was quite sudden. :) The steel is indeed thin and threaded, and I did notice that the red lock collars would frequently lose their torque, and that there was some play between the damper and the lower sleeve. I always thought it was bad...

As you can see, the bottom 6 inches of the sleeve are double-ply steel, but from inside it the long sleeve is a threaded single ply. I suspect this design gives the top edge of the reinforced wrapper a strong lever to put stress on the sleeve--- together with the threaded damper, these probably acted like a scissor to slice through the thin sleeve.

The manufacturer was JIC, and I think after I get these repaired I'm just going to sell them off and get something else. Terrifying.

Please join the QA team....:)