I'm building up a new hand built frame that I recently bought, and I'm having some trouble with the canti bosses and/or brakes I got.

I found some NOS Shimano XT 732 calipers: https://www.benscycle.net/index.php?m...0e9f3f49f81bdb

and

https://www.sheldonbrown.com/harris/cantilevers/xt2.html

But when I put them on the posts there is space between the brake body and the part with the holes for the spring. The brake is slightly loose, as is the plastic cover and spring. When I try them in the higher spring tension, "Normal", setting the spring twists and pops down to the next hole or to the SLR setting.

Either the step at the bottom of the boss is too long or the bushing inside the brake is too long. Are there different brake boss lengths or is this just a large tolerance difference? I've seen that Bicycle Research has a tool for milling the boss and step: https://www.sheldonbrown.com/harris/cantilevers/xt2.html but I don't want to do that, if this has something to do with this brake.

Are there washers for this? Any other suggestions?

Make sure there is no paint above the spring plate on the canti boss. Remove the spring cover and spring and slip the brake arm over the brake stud. it should slide all the way down to the shoulder on the stud with about .010 of the stud protruding above the brass bushing in the brake arm. Don't use a file to clean up the stud use 400 grit w/d sandpaper.

Those old XT2's were great brakes I still have them on 3 of my bikes

Paragon offers 2 lengths for Shimano brake bosses.

That's interesting, I wasn't aware that shimano had made changes to their canti brakes in 2008. But last I looked neither HJ or CWay were offering two different stud lengths.

If the Paragon stud is a bit longer and that is what his builder used it could be the problem