I believe that they were made by Altenburger from the outset, and that the ones marketed by GB were badged accordingly.
A friend bought some when they were current (1960's?) and he reckoned that they were very poor in terms of function and durability. Whether this was representative of these brakes, or he was just unlucky, I don't know.
Neil Foddering Weymouth, Dorset, England.
>From: Harvey Sachs <hmsachs@verizon.net>
>To: seaneee175@gmail.com,Classic Rendezvous
><classicrendezvous@bikelist.org>
>Subject: [CR]Synchron Brakes- How do they measure up
>Date: Tue, 13 Feb 2007 21:13:26 -0500
>
>Sean Flores wrote:
>
>I was taking a look at a set of GB Synchrons on ebay and was curious if
>anyone has had any experience with these? They look like an early
>pre-cursor to dual pivot. I know they were also later manufactured by
>Altenburger (sp?) as well.
>
>Anyhow, if anyone knows how they stack up against modern dual pivot, or
>older sidepull and centerpull, I'd love to hear it.
>++++++++++++++++++
>I keep a pair around the house as eye candy for those who think that dual
>pivots are new. But, I also installed and used a pair on a first series
>Moulton (little wheel), where they were a vast improvement over the
>original sheet steel long reach sidepulls. They were about the only
>period-appropriate alternative for the Moulton, whose front suspension
>objected to center pull hangers, and whose rear suspension just didn't
>clear any of the other brakes I had lying around.
>
>These were built for wider rims than modern dual-pivots, and longer reach
>than most. The "feel" is much harder than modern units, in part because the
>levers don't have the return springs to counterbalance the brake springs.
>
>My sense has been that the GB and Altenbergers are identical. I have
>suspected that the GB was a rebadged Alt, but it could have been the other
>way around. By the way, the tourist levers for these are pretty nice, too.
>
>harvey sachs
>mcLean va