i had a coaster brake arm as a lever on it's first incarnation. they're about 4" long.
if you look at my picture closely, the hole on the left near the spring is where the cable attaches to, then wraps around the homemade pulley. this gave me a pretty good pull, but still not enough. i could pull the brake lever in as hard as possible and it barely slowed the bike. if i had more leverage, it'd probably snap the cable.
a bigger pulley and a motorcycle lever could work, but it would still put a lot of pressure on the cable. ya gotta remember that the brake is usually activated by a chain, and the front sprocket gives it a million times more leverage (give or take a few hundred thousand times...)
the main problems i encountered, were too much rotational travel before the brake activated, not enough lever strength, and trying to dial in the re-setting action of the brake itself.
i thought that the brake cone and clutch cone wouldn't have to be modified like the original coaster brake mod post illustrated, because the shimano parts were one piece so they didn't have to be welded, but it still had some unwanted properties.
namely, when the bike was pushed backwards, the sprocket position would change and the cable would slacken and come off the pully.
if the brake was applied lightly, it would sometimes stick, wouldn't fully release, and then it created drag.
i tried a bunch of different set-ups, rigged up linkages, etc, and never got it to work properly or reliably.
if someone else figures it out, cool, but i'm done with it.
another thing to consider is the type of hub you're gonna use. DO NOT use a crappy hi-stop or anything that comes on a cheap bike. those hubs are notorious for seizing, cracking and over heating, and that's not something you wanna have happen on your front wheel.
a sturmey archer drum brake ranges from 50 to 70 bucks, depending on the model, and that's the way i'm going for all my bikes.
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