Quote:
Originally Posted by Curtis in MA
I'll probably get in trouble for this but I'm not a break guy.
If you center or arch the shoes perfectly, then put the drum on and turn the adjustment wedge even one click, don't you change everything?
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Curtis, I understand what you are saying however you probably need to take a moment and study how the system works. In theory, you have a 360° round surface of the brake drums. When applied, the brake shoes do not contact all 360° of the drum. For the sake of this discussion, let just assume the rear shoes touch from the 10:00 o'clock over to the 2:00 o'clock position of the drum, ...and from the 4:00 over to the 8:00 position. Theoretically, the centerline of the shoes needs to be at the centerline of the drum at 12:00 & 6:00 position. When the brakes are actuated, the centerline of the shoes (which are at the 6:00 & 12:00 position) push directly towards the drum, and the tracks cause it to go in a straight line towards the drum. Now if the tracks are worn or mis-shaped, it allows the shoe to engage the drum off-center. This allows one end of the shoe to contact the drum with more pressure than the other end, ...which decreases the braking friction. Now to complicate the matter, if the axle housing race is worn, this allows the brake drum to be higher than in the correct centerline of the shoes. Let's just assume that the hub bearing and the housing race is collectively worn just 0.020", that means the bottom shoes engages quicker (by 0.020" of travel) and so more friction happens on the lower shoe and the upper shoe has little to no friction pressure. I trust this is helping you understand why without proper tooling and methods that ensure everything is within proper specs, it is only by luck that you will have quality brakes on a Model-A like they were originally.