Re: 1972 DS7 The Long Road
Hi clem, really enjoying your build. I'm signed up. I have a real appreciation for anyone sorting out their own rear sets. I think you have to do it yourself to appreciate that there is a lot more to it than it might seem at first. I wanted to mention one of the problems with pull rod mechanical systems in case you haven't sorted it through.
The problem lies in the fact that, if the pull rod pivot (at the pedal belcrank) and the swing arm pivot are not coincident , the required rod length distance changes as the suspension moves through it's travel. If the pull rod pivot is both very close to the swing arm pivot AND very close to being on a line drawn between the swing arm pivot and the brake arm/pull rod pivot, AND the swing arm rotation is small, the problem is insignificant. Move even a little bit too far away, and the problem becomes noticeable.
The up shot is, if the above criteria is not considered, there will be oscillation in the brake pedal as the bike goes over bumps and the suspension moves. This occurs in the factory set up, but it is so small it is not noticeable (at least by me)
You can observe this very easily. support your motorcycle on the center stand, remove the shocks, and move the suspension through its travel. You will see the brake lever move. If you run a very tight pedal set up, that is the "up" pedal stop is adjusted for a low pedal and the brake rod adjustment is set for a very short "throw", it could be possible to engage the brake with large suspension deflections. You can observe this also by clamping your pedal in one place while the suspension is at ride height, and then moving the suspension through its travel. You will see the brake arm move. Whether this is a problem or even dangerous depends on all the variables.
I really hate an oscillating pedal, and performance riding with one is out of the question. I have built quite a few rear sets and if I have to keep the mechanical drum I use a cable system if I can't either keep the factory pivot or dream up a new one with very close geometry. Cables have their own issues, but are super flexible in geometry possibilities. Pull rod systems are really rugged and reliable, even elegant in their simplicity but you can not escape the kinematics required to make them work properly.
Keep up the good work - DS-7's are a BLAST!!