Note: In this article is shown, how to craft a torque plate for the IS2000 disk brake support. In the online magazine "Fahrradzukunft" also an article (in German) was published, which showed the making of a torque arm fitting on a front rack thread. Interested? Click here!
I wanted replace the front V-brake on my winter bicycle with a drum brake, because a drum brake features constant brake action. I had problems with non working V-brakes causing in compressed snow between arms and rim. So, a V-brake n winter is far away from being constant.
Drum brakes are working a little bit softer, the brake action comes slower and their weak point is the fading on long downhill drives. But in winter? In the Danube valley? No hills? Ok, for winter commuting the right solution!
A 90mm drum brake with integrated hub dynamo is provided by Sturmey-Archer. Also they offer a 70mm version. I used the 90mm version.
God... but there's a lot of torque, which must be held. For that, it has a long riveted lever, which must been fixed with a band clamp. This clamp doesn't fit on suspended forks and over that, it seems to be made of trumpet sheeting! It would be easy, making such a clamp by myself, but the delivered version seems wishy-washy and then... how would seem a tinkered version?
But suspended forks provide in the most cases an IS2000 mont. I can argue from this...
- ...that the fork generally can take the torque of a full braking and...
- ...the IS2000 mount can take this force!
Thus, such fork can be equipped with a drum brake, if it is possible to give the torque to the IS2000 mount.
A piece of flat bar, made stainless steel (e.g. 4mm x 4mm, 150mm long). You also can use carbon steel, if you make a antirust coating afterwards.
Stainless steel screws, M6 DIN 931 in A4-70 or A4-80, alternatively machine bolts DIN 931 in steel 8.8
First, we mount the front wheel. Now we need the flat bar. It is to curve 90° in a long and a short blade. Now we turn the torque arm of the hub a little bit back to get place for a fitting the new part. The place for the opening to mount the torque arm.
With a drill, needle files and a lot of patience, the opening will filed. It must sleeve over the torque arm, but it mustn't have clearance! The best way is: file and try, file and try, file and try... again and again! Note that a hole is easy made bigger but very hard made smaller! (point D in the picture)
If this is ready, a new try and the position is to be fixed. Note, that the upper blade touches the fork (point A in the picture). Now mark the position of the upper screw (B in the picture). Ok? Drill the holes in 6,1mm diameter and then burr it. Then mount it, brake a little bit and press the bicycle a little bit forward. Now mark the position of the second screw (C in the picture). Now take it apart and make the hole, like you made the one before. Now it should have zero-play! Now, the two blade can be shortened, rounded and burred.
Now the complete stuff can be mounted. I prefer stainless steel screws with self-locking nuts. There are also forged alu screws available which have nearly 800 N/mm2
But talking about weight on a winter bicycle is senseless, if you are cycling with studded tires like me!
The Bowden wire fits between our new torque plate and the torque arm.
An old spoke will make a good guide lug for the Bowden wire.
Finally a general view of the other side
This constrution is not calculated. It's made basing on experience. I think, it's stronger than the original SA clamps, Sturmey-Archer part numbers HSL 702 or HSL 703.
Meanwhile, this part in mounted in another bicycle, because my winter bicycle changed. No problem, it fits also in the new fork. It lasts 5 minutes and all was done.
The used stainless steel is a 1.4571 (V4A)! But a 1.4301 (V2A) also would be god for that. The screws are made of strain hardened stainless steel with 700N/mm2, a little bit under a 8.8 screw.
Please do not use screws from a diy-store, they are scrab! They mostly have only 4.6 (400N/mm2), thus the half solidity!