Mitsubishi Pajero when i start the engine it go on but when i shift the gear to reverse or drive it just cuts

That's strange, I take it everything is free at the brakes you have changed and you have not disturbed the gear linkage.check your fluid level on auto box is ok,other than that you may need to seek professional assistance to establish the cause,as could be inhibitor issue or something simple that has been dislodged when you have carried out your brake repair .