That allen head screw, on the top of the steering box, seems to have more to do, with the centering of the steering wheel, than removing the play from the shafts. Though it does have some effect. Like BH said, overtightening, can cause serious, stiffness in the steering. Have had some luck loosening the lock nut by the steering box imput shaft and tightening the spanner type ring, a little. But don´t know, if I´d try it, on my daily driver, mostly on my fun trucks. Book says the box, has to be removed and the spanner adjusted, while turning the imput shaft, with an inch pound torque wrench.