Brake caliper chatter during braking and/or low speed turns

Give this a shot.
Try cleaning the rotors again with scotch brite and a solvent from below.
From Michael Morse at www.vintagebrake.com/tips.htm

DO NOT use aerosol cleaners-some leave residues that promote glazing.
Continued glass beading of rotors will optimize performance.
When changing pads, always prepare the disc rotors by cleaning with an aggressive scrubbing with Scotch-Brite (steel grade) abrasive pads, 180 grit sandpaper, or glass beading (preferred) to remove boundary layer deposited by previous pads. Rinse with MEK, denatured alcohol, or acetone.

MEK works well, but is some seriously dangerous stuff.

Folks,

I removed the caliper and put the wheel on the axle spanning between two jack stands. I taped a chopstick and minimized the gap between the tip and the brake disc--essentially the smallest gap I can perceive with my 20/20 vision. Spinning the wheel, I saw no discernible change in gap size. I know this isn't as precise as dial indicators, but I really don't think that there is a significant warp in the disc. There was no issue with the disc before my steering stem bearing project, I never jimmied the wheel while it was off the bike, so it SHOULD still be good. During reassembly I decided to put the brake pads on opposite sides just for kicks. The problem persists--rattle/chatter at low speeds while moving the handlebars and a light but audible brake drag.

Could my piston not be returning for some reason? The fluid and dust seals looked good when I installed them, the piston is new... the piston certainly returns a LITTLE bit because when the brakes are off it feels like the brakes are off.... what else could cause a piston to LIGHTLY drag on the brakes?

I will scrub and clean the rotors like F64 suggested. I am also thinking of buying new brake pads. Anything to look out for there in terms of what supplier, materials, what is quality, and what isn't?

Did you happen to walk the bike around with the caliper off when you did the last symptom testing. Did you check the axle for straightness. Just rolling it on a flat surface like a kitchen counter top would probably show if it’s good or not. Personally I think cleaning the disc won’t help. I’m sure after a few hard stops and heat anything left on the disc would be gone. Did you check the wheel bearings? How about the speedo drive. It might be the problem

Folks,

I just walked the bike around without a caliper attached. The sound still happened!

A while ago when this problem first started, I considered the idea that the front fender was rubbing against the tire, so I inspected every bit of the tire and I found no wear/scuff marks. Removing the fender isn’t that big of a chore, so I thought, screw it, let’s take off the fender. Guess what—the sound stopped.

So, somehow the fender was rubbing on the tread of the tire while braking and turning at both high and low speeds. Did I bend the fender somehow while I had the front end disassembled for the stem bearing replacement? Perhaps.

Thanks for the advice so far, all. I’m itching for a ride so I’m going to head out around town without a front fender. I realize the front end is a little weaker now without the fender.

Does anyone have an idea of:

1. Why the fender would do this ONLY while turning and braking?
2. How to fix this problem?

Do you have the right tire size on the wheel? Any pics of your wheel and Fender setup would help a lot...

Make sure your fork tubes are mounted correctly. Go thru the process in the pages of the manual I posted. Aslo as scirocco mentions check the tire size.

Front tire is a Cheng Shin 3.50-19 57N.

Is this the correct size to have?

Should be ok. Factory size is 3.60-19. Similar to a 100/90-19