Bicycle Mechanics - Too short brakes?

I'm trying to install a NOS set of XT-2 cantilever brakes on my bike. It's a Trek hybrid that I've had Avid Shorty 6 brakes on for a while without an issue. The problem that I'm having is that the part of the caliper that slides over the frame boss is significantly shorter on the XTs than it is on the Avids. It's so short, in fact, that the boss protrudes out beyond the caliper when the brake is fully seated on the boss. It's preventing the mounting bolt from seating on the caliper, so the brake is free to move all over the place.

In the first pic, the brass bushing is the innermost part of the caliper, and the steel boss can be seen sticking out just inside of it. Same exact thing happens on the old Schwinn hardtail I tried it on. Any idea what's up here, or what I can do about it?

you should go down to your lbs and get a slightly shorter set of studs ... take those with you so you get the same thread design.

Your LBS should also have shims for just this purpose, too.

you should go down to your lbs and get a slightly shorter set of studs ... take those with you so you get the same thread design.

Uhh, the bosses (studs) are part of the frame.

Your LBS should also have shims for just this purpose, too.

Do the shims go on before or after the brakes?

I think they'd go on after because otherwise the locating pin might not seat properly.

It's strange that the XTs are so short, though, I didn't have any problems with mine which means that either they are different to yours, or that I would be unable to use Avids in the future, the latter here being well worth remembering.

Why do you want to change them out? Are the Avids worn out? If I understand correctly, you're not intending this to be a bling-bike...

Anyway, the shims may as well go on afterwards. You could alternately grind the braze-ons down half a millimeter if you have the right equipment. If you do it right it won't hurt the threads, and you'll still be able to mount other canti brakes like the Avids.

Why do you want to change them out? Are the Avids worn out? If I understand correctly, you're not intending this to be a bling-bike...

Anyway, the shims may as well go on afterwards. You could alternately grind the braze-ons down half a millimeter if you have the right equipment. If you do it right it won't hurt the threads, and you'll still be able to mount other canti brakes like the Avids.

I picked up the XTs because I wasn't totally satisfied with the Avids (though they were more than satisfactory) and I wanted to try something different. My hypothesis was that the old, chunky style of brake pad was superior to the new, slim style of pad in the brake squeal department. I was also hoping that the XTs would mount up to the bosses with a little less wiggle than the Avids, but that certainly doesn't seem to be the case.

I'll give the shims a try. Thanks for the suggestions everyone!

I think they'd go on after because otherwise the locating pin might not seat properly.

It's strange that the XTs are so short, though, I didn't have any problems with mine which means that either they are different to yours, or that I would be unable to use Avids in the future, the latter here being well worth remembering.

I think you're right about the shims going on after the calipers. I found this picture on Sheldon Brown's site that shows a black spacer in between the caliper and the bolt. Not sure if that washer came with the brakes originally though, because I bought mine on eBay and they didn't come with any hardware. Do your brakes have them too?

Anyway, I think you wouldn't have a problem mounting Avids on your bike in the future if you decided to. They seem to just be designed a little longer than the XTs, but their mounting bolt is beveled to guide the caliper from the end. Hard to explain, but I think it would be fine.

Maybe the XT's were supposed to come with washers originally?