On my daughters bike, a trek wsd hard tail, I have fitted some disc brakes.
The brakes were an old pair of Hayes stroker I ran, which were ok, nothing too unusual about them.
The upgrade saw a new set of wheels, bomtrager at850 disc specific. These were brand new.
The rotor was an acquired one, a used 160mm, a plain round with round drilled holes through it.
Putting all this together has resulted in the most unbelievable squealing brakes I have ever heard, without a great deal of bite.
I can’t isolate any specific part but wonder if the rotor might be to blame as the braking signs now showing aren’t entirely consistent with what was already evident. If that is the case, is that likely to improve as the two bed into each other?
The other option is to try the Hayes rotor I still have on my bike, that was part of the system?
Or could it be the pads, I did bleed them when swiping them over but always remove the pads when doing so, so can’t imagine they are contaminated.
Any advice or tips appreciated by myself, and my neighbours!

Thanks

Clean the rotors with brake pad cleaner (i.e. isopropyl alcohol) and put on new pads?

Squealing is from either contamination or lack of friction and the pads glazing over the disc . Give the disc a good rub down with aggressive emery cloth in a cross hatch way, so it allows the disc the bite the pads and ride it fast and get some heat in them.

If the disk ‘spokes’ are angled so they are in compression under braking, can you turn the disk the other way. It may be a chatter effect, possibly made worse by hard pads.