Manual front Disc Brakes?

mvh said

Discs always require more pressure than drums, because drum shoes are designed to be "self tightening" -- as they grab the drum, the rotation pulls them in tighter, increasing braking force without requiring as much additional pressure.

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This statement is only true of the "leading shoe". On a typical drum brake, the shoe in the direction of travel becomes the "leading shoe" if the wheel cylinder is at the top of the backing plate. I did a brake job on a '55 New Yorker that had a twin leading shoe front brake; it had two single ended wheel cylinders connected by a metal tube. FWIW, the rears were single leading shoe design. When the parking brake is engaged, the rear shoe pivot point is at the top.

As far as more pressure goes, I can't say. The '73 Dart mordor I converted to disk brakes already had a DB master cylinder on it. I do not recall any increase in effort needed after I installed the single piston floating caliper units. Actually, IMO in typical stop-and-go traffic, effort with disk brakes stayed fairly constant, whereas with drums, more effort was needed to get the same stopping effect towards the end of a trip.