if E is the length along the slide, and W is the width of the slide then the condition to guarantee free sliding is myu < E/W. If myu >
2*E/W then it will lock up no matter where it is loaded. in between it may lock up dependig on where it is loaded. A good approach is to put two sleeves on one rod, and then have a preloaded third bushing on a parallel second rod. That third bushing should be designed to be stiff in the direction that will oppose rotation, and soft in other directions/ rotations so that it can accomodate shaft misalignment. I use flexures for this since they have no slop or backlash.