Upgrading the brakes on a vintage bike

The Issue

After years of postponing I started this autumn to upgrade the brakes on my vintage Freddie Grubb Tourmalet.
The bike was originally equipped with Weinmann 780 calipers and 27.5" wheels (which are actually — due to different measuring — a tiny bit larger than the now common 28" wheels). The frame and fork have plenty of tyre clearance, which means that the brake calipers need to have rather long arms. The Weinmanns provide just that. What they don't provide is braking power. They come with a simple single-pivot design and their alloy is prone to flexing.

The Options

So, what I wanted were calipers with a double-pivot mechanism. The choice of historic components is not very exciting: when the double-pivot design became common ca. 1990, there was apparently no demand for long-reach brakes. So, there are basically 2 options for modern double-pivot long-reach brakes: Tektro R559 and VeloOrange GrandCru. However these come with a recessed allen key mounts and thus can't be mounted on a historic frame with simple holes for nutted mounting bolts. Although they can be modified — if you get hold of some special parts — I decided to go with a third, seemingly easier and cheaper option:
I ordered a pair of ZTTO AS2.6D calipers from AliExpress for 20€. Although they are also equipped with recessed allen key mounts, it's easier to convert them.

Adaptation

For anyone facing a similar situation I will describe the process: The front calipers comes with a long bolt which can easily be mounted at the rear. (For cable routing reasons I ended up mounting it facing forward a.k.a. the wrong way. This has, in case of my frame, also the advantage of bringing the pads a bit closer to the wheel, as the arms are actually a bit too short for the Tourmalet.)

Next task was disassembling the rear calipers to replace the original bolt with something longer. First I removed the right torx screw to remove the front, right caliper. Then I used a screw clamp to force out the bolt. The bolt can be replaced with any M6 bolt with hexagonal head in sufficient length. I ended up with a 60mm long bolt from my local brick and mortar store.

As noted before, the brake arms of the ZTTO calipers are a bit too short for my Tourmalet frame when equipped with 28" wheels. I solved this issue in an inelegant way by milling the holes for the brake shoes with a Dremel. Works. For cable routing reasons I mounted the rear brake reversed, facing forwards.

Thanks go out to Christian and Sebastian at the Church of Bikes, who helped putting the final pieces together, provided me with advice, opinion and a Dremel, and showed me how to properly wrap a handlebar tape.