I have just done a rear disc conversion on my impreza sport and now every time i go over a slight bump or divot in the road the back end steps, it moves all over the place and is highly annoying, being that its only a lowly sport it does not have rear anti roll bar, everything was straight forward swap and bolt over so really shouldn't make a difference in its road manner

 

Bump for any ideas ???

 

Check everything you've touched over to be sure it's all tight, look for play in wheel bearings, get an alignment check. Might even be a good idea to see if there's any play in the topmounts.

J.