I've gone back and watched a couple of the Brothers Trucks videos on YT about upgrading to a dual master cylinder. Some of those videos are such bad quality as to be difficult to watch. The one video where he installs the new kit under the truck, though, did answer one question for me. When he removed the original single circuit cylinder, the actuating rod came out with the cylinder, not seperately. That tells me that it is attached to the piston in some fashion (I don't have my old one or I'd take it apart and look). It makes sense to me that the brake spring is there to help the small master cylinder get the pedal back to the correct position.
Now, when he installed the new dual circuit master cylinder, he first installed the new actuating rod to the brake pedal arm, then installed the new cylinder, slipping the rod into the end of the housing. He then adjusted the length of the actuating rod to get it close to the piston, but leaving just a little free play (for heat expansion he says). At no time did he do anything with the original brake pedal spring. I have to imagine that the spring has that pedal arm up tight against the brake light switch.
I'd sure like to see pictures of other trucks that have had this conversion done to see if the owners changes the pedal spring in some way (either its size, or position), or...etc. At this point what I'm thinking of doing is attaching a 13/16" thick rubber block to the toeboard just below the brake light switch to give the brake pedal arm something to stop against, or adding a rubber stop to the arm similar to the clutch pedal.
