I started driving my Darrin and found the brakes difficult to stop. I didn't arc them at the time since there worked fine 6 years ago when I was driving it before the restoration, what a mistake!!
I arced the fronts and what a difference. Pictures tell the story!!
pic 1 arcing machine, this is what they look like! You must first use a micrometer on the Drum for the actual diameter, then set the machine up for that diameter. Then you slowly arc the shoes till they match the drums - 100% contact!!!
pic 2 first pass shows a high spot in the middle.
pic 3 shows only about 1/4 of the shoe making contact.
pic 4 after taking a few more thousands off, we are getting close!
pic 5 100% contact. They will act like you have power brakes!!!
The machines are hard to find, however, they work great.