After a bit of advice. New frame has IS brake mount on the rear and on attaching the rear brake, I can’t seem to move the caliper outboard enough so the pads aren’t touching the disc.

Looking at the frame there’s a good amount material pushing the mount toward the wheel. I assume this is a case where the frame needs facing, never needed to have this done before, hence the question.

Crap pic to try and show what I mean:
[url=https://flic.kr/p/RWzAEc]Brake Mount[/url] by Sam Dexter, on Flickr

Looks like the bottom of the rearmost bolt hole is pushing the adaptor at a funny angle as it looks bent/wonky.
I’d be looking at getting them checked/faced.

File the holes wider to move the calliper over a bit

I’ve had a couple of frames or forks with tricky alignment. I modify the adapter rather than the frame. Seems less drastic.

Yep, get it faced, standard workshop job and any decent bike shop will have the tools.

I modify the adapter rather than the frame. Seems less drastic.

That most likely makes the adapter useless on any other bike, and means that if you change the brake adapter you have to do it again. Facing IS mounts is standard frame prep, it doesn’t damage the frame, usually just removing a little excess paint and maybe a tiny bit of metal in the same way that facing a BB or headtube does.

There’s not much material to remove, 0.5mm or so, until you get to the plate part of the mount. You might need to do something with the adapter.

Thanks chaps, I’ll get it faced and go from there. The adaptor worked with the last two frames, which were earlier versions of the new one.

If that doesn’t work, I’ll try messing with the adaptor. No way I’ll be filing the caliper, they’re new E4’s!