Reaming Steel Brake Mounting Points
 

I just got a Tektro R556 brakeset for an older (late 70's-early 80's) Schwinn roadbike. The bolts on both brakes fit nicely inside the drilled mounting points (what do we call those?) in the bridge and in the fork, however the nut, which is designed to recess inside the hole, is about 2mm or 3mm too wide in diameter to fit.

Is it alright to ream these drilled mounting points? If so, what's the best method? Drill bit with some cutting oil? Reamer with cutting oil?

Hole in the back of the fork you can just drill a bit bigger. The one in your brake bridge is a little trickier since you just have a tube for a brake bridge, it needs a couple of those of those curved washers for reinforcement.

Common practice is to use your new front brake on the rear with some curved washers and a regular nut, and use your new rear brake on the front, after drilling out the back of the fork (drill and cutting oil will work fine), and using an extra-long recessed nut.

I just drill them out. (Be careful to go only half way.) The front is a piece of cake to do.

The rear is a bit tricker because there isn't room enough to fit a drill. I just clamp my drill bit in a vice grip and rotate it back and forth by hand. It's faster and easier to do than you'd expect.

I don't worry about using curved washers either. Look at the size of the flange on the recessed nut. It's so small that it fits nicely against the brake bridge tubeing.

I would get a set of Metric drill bits first then go for it.

if these are NEW brakes check with the seller and see if he has nonrecessed or nutted versions. the fork is one thing but I would not drill a brake bridge. if you just drill the bridge straight through, even with the concave washers your brake is likely to move up and down.

on of the Gents in C&V recomends using something called a reverse drill bit. try searching the topic.