Paul, arc grinding is exactly what Jerry explained, matching the outside coutour of the brake linings to the exact inside diameter of the drum. The result of this is that there is full contact between the brake linings and the drums immediately, without waiting for the high spots to wear off the linings, gradually increasing the contact area until full contact is finally achieved after long use.
Don't believe anything you hear about arc grinding not being beneficial. That's the official politically correct line now that arc grinding is actually illegal in some places, like nutty California where I live.
I'd like to tell you how I learned this. I have a 1932 Ford roadster street rod. When I first built it about 8 years ago it was plenty fast but it wouldn't stop. It was plain scary. It has GM "Metric" front calipers and 11" Aspen-Volare rotors adapted to a Ford beam axle and 10 inch Ford drums on an 8" Ford rear axle. The MC is a 1985 Thunderbird aluminum unit with a 21 mm bore. A Speedway Motors adjustable proportioning valve is plumbed into the rear brake system. There is no room for a booster.
I went into a very long established local brake supply business and asked about upgrading the stopping power, perhaps with ceramic pads and shoes. The answer I got was "Let's try asbestos first and see how that works for you. We can still get it and it's way less expensive than ceramic".
That totally solved the stopping issue. Imagine a business helping a customer find the least expensive solution to a problem. Wow, that's old school service!
My restored '36 Chevy pickup still has the asbestos shoes I put on it in the early 1970s. As little as antique trucks are driven a set of brakes outlasts the guy who installed them.
