Hi Lin, to my knowledge there is not a specific torque for the U bolts. If they are the original ones you may have to use a spacer of some sort between the nut and the bottom plate to keep the nuts from bottoming on the threads, I tighten them equally, keeping the bottom metal plate parallel with the bottom of the spring until the rubber buffer is well compressed but not contacting the Axel housing. A bit of practice and you will get the hang of it. I hope this helps a bit,--Fwiw--Keoke