I replaced a rear rotor and pads and also just pads on other side. I didn't replace rotor on other side as first caliper carrier had to be cut off and I didn't have time to do same of other side hence I just changed the pads on one side.
The rotor I didn't change was in fairly bad shape, the old pads were worn to the metal, it had a lot of putting, scoring , grove etc.
Also the pads were pretty tight fitting into the shim, I had to grind them down on one side but weirdly not on the other although pretty tight fit.
Now I'm sure my cars handling is a bit wobbly, it slightly pulls to the right also.
Why would this be, pads too tight or the bad rotor that's still on not liking the new pads it has?