The process of quasi-parallel shock re-formation is investigated using one-dimensional hybrid simulations. These simulations are used to study the coupling of a beam of ions reflected at the shock to the incoming solar wind. We have constructed a simple simulation configuration that allows us to control the properties of the background plasma and of the reflected ions. The simulations initially do not contain a shock, but rather include a background plasma, corresponding to the solar wind, into which we inject a counterstreaming ion beam, corresponding to shock-reflected ions. We investigate the length and time scales for the coupling of the reflected ions to the background plasma as functions of &thgr;Bn, beam density, and beam temperature. This coupling can lead to the formation of shocklike structures upstream from the injection location which we associate with quasi-parallel shock re-formation. In addition, we have perturbed the upstream plasma in a controlled manner to study the effect of upstream waves on the coupling process. We find that the coupling length and time scales vary systematically with the upstream magnetic field direction, &thgr;Bn. The coupling occurs at roughly the time and location where the injected ions become deflected transverse to the shock normal direction. Also, as seen in previous quasi-parallel shock simulations, the reflected (injected) ions become trapped downstream of the newly forming shock by the growing perturbations. In this way, shock-reflected ions may contribute directly to the downstream ion temperature. ¿ American Geophysical Union 1991