Wrong frame hole
 

The hole for the bolt that holds the rear brake on the frame is drilled top-down and I found out the reason reading a post on this forum. The frame is designed for Mafac brakes and the same bolt holds the fenders also. What could I do to use a new pair of brakes? I don't want to drill the frame. I thought about using disc rear brakes but the frame is old enough and it has no mount points for disc brakes. Any advice could be very helpful.

Dia compe made a special brake mounting adapter for these rear bridges. Someone posted a picture of one here on this forum about a month or two ago. maybe you can find a link to that thread and picture. Finding the actual part may be a bit more difficult, but there are probably thousands of them around on rusting frames of that era.

In the meantime you might be able to make do with 2 angle brackets, a 6mm screw, and a 6mm cap screw.

Assuming there is clearance and you cannot find the proper adapter I would consider this a good candidate for rigging up some sort of home made drop bolt. http://sheldonbrown.com/home-drop.html

Unfortunately, you'd still need to change the the direction by 90 degrees somehow.

Thanks a lot FastJake, but I have already read that article and I'd preferred something more elegant.

Do you have a drill press and a bit of hand skill? If so, I'll detail how to make the part you need fairly simply.

Otherwise, you'll need a friend in Pittsburgh who'll visit a very unique bike shop (sorry I forgot the shop's name) and dig one up. Maybe if you offer the Hillrider a few beers he'll make the pilgrimage for you.

threadless shoes
 

Old cantilever, Mafac centerpulls, deore brake shoes pull an orthogonal post towards a hole. Maybe you could torque one to the bridge hole, but I would check it frequently.

Tell me how could I do it please

Consider drum brakes , now Sturmey archer has a 8~9 speed compatible cassette
[if frame is wide enough]
I've used a screw on 7 speed for decades. 126 wide space.

Here's the thread with the picture, about 2/3 of the way down:
http://www.bikeforums.net/showthread...-Brake-Schwinn

Yo, supplementing my inscrutable post about things which hold threadless brake shoes with post about brakes your frame came with; eBaY item 270945089681 (you can search clb or "clb -tones" in the cycling category and find ridiculously priced units as well as ~$40 calipers postpaid.) The shoes look like forged dural and clb is a serious firm, and I was tempted by their stuff when it used to be available from my framebuilding supplier. French engineering is always intriguing.http://bikeforums.net/attachment.php...hmentid=244136http://bikeforums.net/attachment.php...hmentid=244137