Hi everyone

At the moment im experiencing problem: if i drive at speeds greater then 70 kmh and i start breaking, i get noticable shaking of the steering wheel.
Now i put new mags, which are heavier then facotry ones, and shaking is worse, but driving at highway speeds is ok, no shaking (as i guess i should ve get with bad balanced wheels)

Also i recently failed WOF due to my steering rack beein lose or something. (checked that today, and it seemed to be completely ok)
break pads are new ones
and i think all this shaking started after i hit curb at 60kmh... done around 10,000km since then. cheked thread of tyres, looks to be weared evenly.

So question is, shaking while breaking could be caused by what? most likely?
bad rotors? (how to check them)
bad wheel alignment? (how to check)
both sets of wheels bad balanced?(doubtly)
steering rack bent or lose? or something else?

waiting for replies.