I see Vincent has made one of his usual elegant adaptations of a custom clevis for the bottom mount of a Works Performance shock. It eliminates the adapter to the spring seat I had to make since I used an off the shelf clevis. Due to the pitfalls of making things from scratch I like the Albervin’s idea of a batch build of a proven design. I have to credit Ted Leno, Robert Watson, and Dave Molloy, who pioneered some of the Works adaptation I use. Among the things I found that should be considered in a new design or if someone is doing this on your own are:
The throat depth of the bottom clevis has to be around 29 mm so it can clear the headlight mount tab when mounted at an angle. Less throat depth means that a notch must be cut in the back of the clevis. I reworked one of these Midwest Control clevises by redrilling the pin hole at that distance. It also required adapting the tapped hole in the clevis to 3/8-16. More on that later. One of their 24mm clevises could work by notching. They have deliveries from the UK and some of their stuff is on EBay.
MTC-12L-SS, Clevis and Yoke Ends, Female M12 x 1.75 RH 12mm Pin Holes 12 x 48 Housing Stainless Steel Turned Construction
midwestcontrol.com
The travel of the damper rod has to be limited so that the parts of the damper do not interfere with the Brampton parts. When Dave Molloy sold me the Works shock he machined a 1/2” rod spacer internally to limit the travel. It actually could have been a bit more, perhaps 3/4”. This keeps the good geometry of the Bramptons more like they are originally and out of the area where the lower link drops too far below horizontal at full extension. Removing the original Brampton spring and replacing it with a preloaded coil means that full extension could happen when the front end is unloaded, like cresting a hill, though the damper will slow the motion. The Brampton spring resisted extension since it was constrained at both ends.
Since the damper will pivot slightly, provision must be made for the headlamp stays to be isolated from this motion and allow free rotation. I moved the stays down to an extension of the balance beam mounting bolt and avoided this. It also had the advantage of lowering the headlamp shell and making more room for the damper motion and the light switch knob in the shell.
The stock Works damper rod has a 3/8-16 thread where the new bottom clevis must be mounted, turned down from it’s 1/2” diameter. I experienced a failure of the rod at this place as I have talked about elsewhere. I am making a new rod out of hardened and precision ground 17-4PH, (McMaster-Carr), which is much stronger than the original Works material, and I will be making the threaded end larger at 12mm or perhaps even 1/2-20.
As Robert Watson and others have mentioned, the headlamp mounting tab even on original Bramptons has proved itself to be strong enough for this use over quite a few years, lots of rough miles, and differing damper adaptations. The hook Vibrac shows may not be necessary, but I would feel better if something like that is part of the design as a belt and suspenders feature.
A 12 mm bolt works well for the top clevis in the upper spring mount, and makes it easy to find a suitable metric clevis. The clevis can be redrilled and tapped to use an FF70 which saves space and looks neater.
I found that a 120 pound spring was fine for my mostly solo and lightly loaded Rapide. I weigh 165 lbs. It might have to be a bit more for two up touring, though the preload adjustment helps here. The spring dimensions are about 2-3/8” diameter and 6-3/4” long. Larger diameters will make interference with the cycle parts a problem. Eye to eye length of the collapsed shock with bottom clevis fitted less spring and rubber bumper is about 7-3/4”. Extended length with the internal limiting spacer is 10”. This is plenty of travel and could be less as I mention above. It’s a good idea to test the shock travel out on the bike this way to make sure there is no interference or binding.
