[CR]Update on braze-on mounting of Dia Compe GC450s

(Example: Framebuilders:Norman Taylor)

From: "Adam Hammond" <anhammond@gmail.com>
To: classic rendezvous <classicrendezvous@bikelist.org>
Date: Tue, 29 Jan 2008 15:08:07 -0500
Subject: [CR]Update on braze-on mounting of Dia Compe GC450s

My pair of GC450s arrived in the mail today (thanks James!), and I quickly began to investigate the various things I've been wondering about their suitability for mounting on brazed-on bosses. I've taken numerous photographs, which can be found at the link below, and which demonstrate my findings:

http://www.flickr.com/photos/expenguintamer/sets/72157603815840418/

a) Straddle Cables. My pair arrived without original straddle cables. But I tried some from a pair of Mafac Competititons, and they work just fine. Good news, except, of course, for the fact that these are just about as rare as original GC cables!

b) Bosses. From the mounting plate, it is indeed clear that these are very different from Mafac bosses. They have three "steps" to make way for the ball bearing pivots. I have yet to ask my builder if he's interested in reproducing these with a late and making braze-on bosses for me, but I will certainly do so.

c) Springs. The 450s' one-spring setup presents a challenge for braze- on mounting. But it certainly looks like Mafac springs will work fine. The diameter of the bosses on the Dia Compes seems very slightly smaller than that of the Mafacs, but not enough to cause a problem. They press against the brake shoe in the same way as the Mafacs. I'll just need to get my builder to drill a hold in the mounting boss on which to anchor the spring.

d) Brake shoe attachment. This is a new concern: the diameter of the eyebolt attachment on the Dia Compes' brake shoe seems much smaller than on Mafacs. I was planning on using Kool Stop Eagle 2 pads, but I think they might be too fat. I don't see how one could replace the pads in the current holders. And I'd like the salmon compound.

Essentially, these are Mafac Competitions with ball bearing pivots, a different spring assembly, and a nicer finish. They really are extremely beautiful.

While most of my concerns about these brakes are addressed, I could still use some small parts. If you happen to have any of the following, please let me know:

-- original GC straddle cables -- orginal Dia Compe braze-on bosses with washers for springs -- two Mafac springs (these are available NOS from several stores)

Thanks to everyone who's helped me along with this! And thanks again to James for the brakes themselves.

Adam Hammond
Toronto, ON, Canada