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Drum Bake Issue

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Old 08-30-14, 03:17 AM
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sedition
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Drum Bake Issue

First, I apologize for a cross post. The following post was also made in the mechanic section, but just in case someone with knowledge might look in this sub forum, and not the mechanic one, I risked the wrath of cross posting.
___________
Hey All,

I need some guidance dealing with a drum brake on this (Swiss Military).



I got this bike last week. The read hub needed help. The brake shoe and clutch for the coaster brake were decimated. I ordered/installed replacement parts, and everything seemed to be working fine on the first test ride (went about 2 miles). Today I went out for a ride (about a mile), and things just didn't feel right. I got home, pulled the hub apart, and found some metal shards! After some inspection, the source of the problem was obvious. Two parts of the drum brake shoe were rubbing together. Below you can see the damage. The ring of fresh metal (inside the red circle) sure as hell ain't supposed to be there. I should add the drum brake is NON-functional right now. Previous owner had removed brake handle and brake cable, so the drum was not in use at all during these two rides.



Second, here is what was causing it (again in the red circle).



What is going on here? Why are these two pieces of mental in contact with each other? Is a spacer of some type missing? Does that thread ring need to be seated further down? Any help would be much appreciated!
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Old 08-30-14, 07:22 AM
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Mark Pace
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It looks like the drum needs about a 2mm spacer between it and the hub (on the inside, opposite the lockring.) So you'll need to remove the lockring, and then unscrew the drum. There should also be a spacer on the axle to hold the backing plate (the part with the torque arm and brake shoes) the correct distance away from the drum. That spacer width may or may not need to be altered once the drum has been repositioned, in order to ensure full brake shoe engagement with the drum (with no rubbing when brake is not applied, of course.)
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Old 08-30-14, 08:37 AM
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sedition
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Interesting. I had not considered a spacer on the back side. It does not look like the lockring or drum has been removed in years (e.g. if there is supposed to be one, it's been missing for a long time). Previous owner claimed he had ridden bike (before brake shoe and clutch were toast). Maybe he never actually rode it. Anyway, I had considered a spacer between the race and drum backing plate, but the baking plate and race seem to fit perfectly together without any spacer (or rather that presence of a spacer would interfere with their respective placement). The photo below shows what I mean. The male/female parts in the red/blue circles line-up perfectly with each other. Thoughts? Also, thank you for your input!

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Old 08-30-14, 02:52 PM
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FIXED!

The answer was SO obvious that myself and 3 professional bike mechanics over looked it for 30 minuets (well, me for the last 24 hours)! I took it a local shop this morning. Most of the mechanics were swooning because they had never seen a hub/drum brake like that before (some other wouldn't go near it). We looked at the problem for awhile, and no one could figure it out. Then it just dawned on one of them: NO BEARINGS PRESENT ON THAT SIDE! We all just went "AHHHHH," and leaned back in tacit acknowledgment of his genius. Add the berrings, and the "spacer" is suddenly there! They didn't have a proper bearing cage, so he just sold me a bunch loose ones. I grease packed them and the bearing race at home, and for $4, it's now running great!
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