need some help on disc brakes

[stew198269]

hey guys my first time in here so dont no if this the right section but i have a problem with my disc brake on the rear kinda like a rubbing althought it goes from time to time. when going at fast speeds i can really here it and can only but think what people i pass must think lol. how do i go about fixing this ive looked on youtube but cant seem to find anyone on there that has the same problem . also i dont no if my disc is bent as when looking at the contact point from the disc and the pads the disc bends in words ive tried bending it back out but no luck. if i have to buy a new disc then what size do i get as was blown away when see on ebay there was more than one size my bike is a giant aluxx 6000 im pretty sure by looking online it says im meant to have 160mm discs but when measuring my discs they are 170mm. i did buy this bike 2nd hand so could the person before have put the wrong discs on and this might be the problem with the rubbing? or does it not matter about the size of the disc (160mm 170mm 180mm).
any help pls guys
cheers stew.

 

[subaqua]

close to the hub there will be a measurement in mm , thats the disc size. most discs have some run out so the caliper may need centreing. loosen the 2 mounting bolts that hold it to the frame than apply the brakes and while they are applied tighten the mounting bolts. cures the light rubbing on my MTB with hydraulic brakes .

not sure if it works for cable disc brakes.

no doubt somebody will be along to tell me i am completely wrong though.

 

[SquareDaff]

not sure if it works for cable disc brakes.

no doubt somebody will be along to tell me i am completely wrong though.

It works for the mechanical AVID BB5's on my CX so that "somebody" won't be me.

 

[stew198269]

close to the hub there will be a measurement in mm , thats the disc size. most discs have some run out so the caliper may need centreing. loosen the 2 mounting bolts that hold it to the frame than apply the brakes and while they are applied tighten the mounting bolts. cures the light rubbing on my MTB with hydraulic brakes .

not sure if it works for cable disc brakes.

no doubt somebody will be along to tell me i am completely wrong though.

ok cheers for this been at it all morning and think i have done it. cheers for ya help.
i couldnt find the markings u was on about tho for the propper size of the discs needed but its kul the bike seems to be running fine again for now.