Tandem Cycling - Why does my new Arai drum brake make that noise?

I've installed an Arai drum brake on our Burley Duet. I've been following the instructions found here (http://www.precisiontandems.com/arai.htm), on the Precision Tandems site.

Installation has been smooth and straightforward, so far. But now that the brake is on the hub, and now that the wheel is re-attached to the frame in the rear dropouts, and with the bike currently suspended in a repair stand, I notice a slight amount of drum-brake actuation while the rear wheel is free spinning.

As I turn the pedal and set the rear wheel in motion, the drum brake emits a scraping sound for approximately 180 degrees of each complete turn of the wheel. It is a light sound, but definitely noticeable, the kind of noise that would drive any stoker crazy within 1 minute. The scraping does appear to scrub small amounts of speed from the wheel, but the braking action is not dramatic.

The cable has not yet been attached to the brake's lever.

I've moved the actuation lever back and forth with my hand, but there does not appear to be a location in the lever's extent of travel at which the scraping noise stops. There appear to be only two modes: full braking, or nearly-free rotation marred by the 180 degrees of the aforementioned pad-to-drum contact.

The installation instructions are silent on this matter. Only at this step do they appear to contemplate the precision of the fit:


6) Thread or slide on the outer spacers, locknuts or axle ends but do not tighten at this point. Next move and hold the actuation arm in the "brake on" position while tightening the outer locknut or axle end. This step will help the shoes center up by the tolerances available between the backing plate and the axle.

I followed these instructions. Or at least, I believe I did, meaning that I did hold the actuation arm in the "brake on" position while tightening the nut. Did I do it right? Did I do it enough? I can't say.

Perhaps the most telling clue I can find: With the rear wheel on the workbench, I threaded the brake drum onto the hub. No problem. Then I placed the brake-shoe assembly into the drum. No problem there, either. Then, I held the wheel stationary and began to rotate the brake-shoe assembly within the drum. I did not hear any scraping sound, or feel any resistance, but I did notice a slight off-center eccentricity to the orbit of the brake-shoe assembly within the bounds of the drum's inner cavity.

Is this the sort of characteristic that works itself out after a few (hundred) miles? Or the sort of thing that requires the attention of a trained bike mechanic? Or something else?

Thank you.

Update: I removed the entire unit and re-inspected the drum and brake-shoe assembly. There is nothing obviously out of alignment. Nor does the assembly provide any opportunities for adjustment. The drum is a single piece of machined metal -- no modifications possible. The brake-shoe assembly is a model of sturdy simplicity. There are no parts that can be adjusted without access to the original machining tools. I suppose one could grind on one of the brake shoes, or could stretch out one of the two springs. I wasn't going to mess with it.

So, the whole unit went back on the bike. I took care to thread the drum on squarely, and to center, within the sub-millimeter play available, the brake-shoe assembly's cover plate under the axle lock nut. That's really all a person can do.

With the wheel locked into the frame and the brake's anchor arm secured to the frame's "pac man" anchor slot, the grinding noise was less pronounced than it was before, when I scoped it out for the first time. I installed the brake cable and friction shifter. So, the unit is on and functional. The slight, 180-degree grinding noise is faintly heard, but only when coasting. It seems to fade out when the pedals are cranking. So, I'm hoping that the unit will "find its center" and the shoe-to-drum contact, being very minimal now, will eventually work itself out after a long ride or two. We'll see.

I was hoping for someone more knowlegeable to chime in, but here's my experience:
There's definitely a break in period for the Arai. Best thing is to set it on a couple of long hills even if you don't really need to use it. You should find the braking performance improves after this and I think that it may help to center the shoes. I find about 1/4in of tension can be put on the arm before the brake starts to engage - just enough to snugly hold the quick release stop but not enough that you can't get the thing off. I find no grinding or touching when I spin the wheel - it should be free. After break-in I had to adjust the tension a little as it had loosened up a bit. You should find you get decent modulation on real hills, but you won't be locking up the rear wheel with the Arai.

Tredlodz,

Thanks. That 1/4-inch of tension is about what I need to engage the brake, too. And I was thinking the same thing you were: That a few descents with the brake on would help wear down the "high spots" in the shoes and help the assembly establish a noise-free center. I anticipate needing to adjust the cable tension after a few uses. I'll report back after a few rides.

Take the assembly to a brake specialist and have the shoes fitted/arched to the drum. I have a few vintage motorcycles, and it's an often occuring problem.

They should arch themselves within a hundred miles, or less. And yes, the cable typically stretches a bit with the initial several applications.

This was my experience with the drum brake on our quad.....

Also, be sure you have the correct Arai brake-shoe assembly plate for your hub axle. They make the brake-shoe assembly plate with holes in two sizes, one small, one larger for Santana Hadley hubs (and perhaps others). Conceivably, you could have a plate with a too-large hole, allowing it to move around rather than staying centered.