When you say "10mm" rod....do you mean rod that accepts a 10mm nut?  The hole through the barrel that fits in the rear brake arm is actually a 6mm thread size.


When I built my rear brake rod, I first tried 1/4" stainless rod.  I had to stick it in the lathe to cut the diameter down just a bit to get it threaded to 6mm.  I discovered the rod flexed too much where the rod was bent to avoid the muffler, and the brake pedal was mushy as a result.

I made the rod out of 5/16" stainless, and it proved to be much better (I had to cut the ends down to 6mm to get them threaded).  Going from 1/4" (6.35mm) to 5/16" (7.93mm) doesn't sound like much - but it increases the stiffness by 56% and made a big difference in pedal feel.

So.....using 10mm threaded rod is probably fine - but I believe using 6mm threaded rod (which fits through the barrel in the rear brake rod) proved to be a bit too flimsy.  Having the entire rod threaded doesn't look all that great, and it will reduce the stiffness some as the threads do cut material away.

One possible way to make this work without a lathe and the dies to cut threads on the rod - would be to use the 10mm rod and have someone weld 6mm stainless bolts on the ends......allen head bolts would be easy to get welded onto the ends of the rod.  They could also weld on a nut, washer or stud where you want to connect the brake light.

When you weld stainless, the metal that is exposed to air and not shielded by the gas reacts with the oxygen and turns black and becomes very porous.  It is a problem for tubing or sheet on the backside of the weld - but I don't believe it will be a problem for welding a stud into small tubing.

Sometimes the simple ways are the best.  It doesn't look any worse than some of the things I have seen on factory Norton's or Triumphs from the 1960's.

You could paint the rod black and make it match the spring......or go get some stainless welding rod and make it shiny to match the brake rod.

I fussed with this a long time when I did my bike build.  I ended up hiding the switch behind the right side body panel, and using a bicycle brake inner/outer cable to activate the switch.  The weird thing is the inner cable is mounted solid to the rear set mount and the outer cable is mounted to the backside of the brake pedal....and the outer cable moves when the brake is applied - While at the other end of the outer cable is mounted stationary and the inner cable pulls on the brake switch spring.  It works just fine - and I had to do it that way to keep the cable headed in the shortest direction possible.