the long version of the story is it started with a cherry, intact '78 Moto Grand Touring. somehow, the wheels went to a Trek 620, and then it was downhill from there. New wheels and a Suntour 6 sp, new, wider, ergo bars (I have a back problem) and bar end shifters.

So why not go to dual pivot brakes? I mean, after all, I have a dandy set of Centaurs just laying around, and some newish Tektro aero levers. (the new bars have a cable groove).

Don't get me wrong--I like the Weinmann center pulls all right, but the cable stop on the front flexes, and after (foolishly, perhaps) removing the front reflector--now the top steerer nut keeps loosening. And the cable routing gets in the way of various bags and accessories.

Then the question is, should I drill out the frame and fork for the recessed nuts, or shell out another $50 for some Tektro 539's? Or something similar?

I must add that I am a little intimidated by how thin the rear brake mount would get if it were drilled.

Drilling the fork is relatively easy, though it's difficult to counterbore the back end so the hut sits flush. I don't like drilling the rear because the clearance issues means I have to drill from an angle. Also if the bridge isn;t designed and properly reinforced for the recessed nut design it cn create new complications.

My suggestion which depends on the bolts being long enough.

1- mount the front brake in the rear with a conventional nut.
2- buy a 1" long recessed nut and a 6x1 Stainless cap screw about 1" long (measure everything) to know what you'll need. Cut the head off the recessed nut to make a threaded connector, then mount the rear brake in front, reach through the bottom of the fork and position the connector on the bolt and spin it on as far as possible. Then finish the job with the cap screw.

Of course all this depends on some serendipity, but I've had success with the method a number of times. If it's practical for your bike it's the easiest approach, with zero risk of complications or damage, except for the few dollars spent on the hardware.

Um, get a better cable stop?

Bodging option.. A recessed nut front Brake would be plenty long if mounted in the Back .. use the half round to flat adapter washers ,

that would mount the older brake center bolt add more flat ones if still too long under the regular hex Nut

The cable stop doesn't have to be 100% rigid to be sufficiently effective..

Just remember to swap sides on your brake pads....they may be directional.

What a coincidence, I have just decided to modernize an S12-S with an RSX group, and thought I might look at dual pivot calipers too... I had pretty much decided to avoid the cost of new dual pivots since I have some decent caliper brakes in the parts bin... But, do I go through the effort of drilling. I don't mind drilling the front, but I haven't checked the rear bridgs to see how well it could be drilled.

I also briefly thought of moving to center-pulls, and decided that I didn't want the cable routing necessary for center pulls... unless I ran across a road stem drilled to be used as a cable hanger for center-pulls/cantilevers, like I have seen for a couple of vintage mountain bikes...

All that to say, I am responding to see what others think on the subject.

EDIT: Mine is possibly complicated a bit by moving from 27" to 700c, and I haven't measured the reach yet.

The mounting bolts for Shimano dual pivot brake calipers are available in different lengths. The only difference between the front calipers and the rear calipers is the length of the mounting bolt. Moving the front caliper to the rear is a way to get a dual pivot caliper onto the rear wheel.

To get a dual pivot brake calipers onto the front wheel, what about doing some reach into the part number of the mounting bolts and finding one that would be long enough to swap with the one that came on the rear brake caliper (since you are using the front caliper on the rear wheel?).

I already have some mounting bolts leftover some when I did some changes on my bile and had to get longer mounting bolts for the dual pivot calipers. If I remember correctly the original mounting bolts were a touch too short for my taste, so I had my LBS order some longer ones for me.

A recessed nut brake on a 1973 frame:

An alternative approach is to use the front brake as the rear with an external nut as FB recommended and adopt the rear brake for use in front as follows:

Drill the rear of the fork's crown out to 5/16 " (8 mm), which is easy, and get a long enough recessed nut to allow use of a rear brake directly. Those nuts are available as long as 35 mm which should cover almost any road fork's crown thickness. Here is a source for those nuts: Bike Tools Etc. - 1000's of bicycle tools and parts for the home mechanic!

I used a 30 mm nut on the bike above's fork after drilling it. Both of the brakes are rears that I found at a bike swap. The fronts were probably used for fixies. I had to shorten the 30 mm nut to keep it from bottoming.

Yes, the very long front nut will probably have to be shortened a bit to keep from bottoming even on a rear brake's short bolt. How did you adapt the rear brake? I've drilled out the front hole of a brake bridge using a short 5/16" bit clamped in a Vise Grip and turning it a fraction of a turn at a time. It's laborious but does work and allows you to keep the bit 90 degrees to the hole.

I used a 5/16" bit clamped in a small Vise Grip. It took a few minutes.

On the 'steerer nut' loosening...

Was the mount for the reflector you removed serving as a washer between the locknut and the adjustable race? Because if you don't have a washer (usually keyed) between the locknut and adj. race you'll have problems with the locknut coming loose.

Headset (bicycle part) - Wikipedia, the free encyclopedia

what great ideas you all provide! I ended up installing the front brake on the rear--the little cross bar the brake mounts on is machined flat on both sides, so no need for scalloped washers.

mounting the rear brake on the front was a little trickier. The Centaur comes with a thick nut on the mounting side, and still required a scalloped washer to conform to the stem. That combination did not allow enough of the bolt to penetrate into the core of the stem, for secure fastening. So I removed the nut altogether, and substituted the hefty aluminum block (with a scalloped face) that came with the original Weinmann center pulls. It had to be reamed out a little, because the Centaur mounting bolt is stepped. I also borrowed a thick aluminum washer from the Weinmanns and filed a convex profile on one face that conformed to the curve inside the stem.

Then I took some little torpedo shaped barrel nut (can't recall where it came from), which was short enough to fit inside the stem, and ran it tight with an allen wrench stuck through the hole in the back of the stem. Gooped the threads with a generous application of blue loctite.

even without the original nut, it feels real secure. the radiused washers give it a lot of stability, but it is still possible to rotate the assembly so the shoes meet the rim simultaneously.

It's finished off with Tektro 340 levers, and Koolstop pads--their Campy style, 1/3 black 2/3 salmon. The feel is superb. I admit it's a hodge podge of parts, so it's fortunate that I am not a purist. but if it makes you love your bike, I think it's ok.

FWIW, the Centaurs have just barely enough reach. There will be no swapping out to 700's, without changing the brakes.

anyway--thanks all for your advice. Happy riding!