Rear brake locking under light pressure

[motorcycle_mistress]

Recently the rear brake began locking under light pressure.  I have had several of my friends ride the bike to confirm that the problem is not due to pressing the rear brake lever too hard.  The problem started suddenly, so it's not like it gradually worse.

I have been riding my 1995 GS500E for about 1 year now.  I have had 2 light drops during parking lot practice at very low speed.  The problem began about 2 months after my most recent drop, so I do not think the drop was a factor.  I also replaced the rear brake pads about a year ago when I first got the bike.  I have always used the rear brake in conjuction with the front brake during all my stops and am used to using the rear brake.

I had suspected the rear tire, which is old, (Kenda Cruiser ST 130/70/17 DOT K3VC 529, so that means it was produced the last week of 1999 right?) that has started to dryrot.  But if the tire was to blame I would suspect the problem would have gradually gotten worse as opposed to a sudden onset?

I also suspected the caliper seal was sticking and not retracting the piston.  I thought maybe when I hit the rear brake and let go, the pads were staying against the brake disc, then the pads were wearing slightly as I rolled off.  Then the next time I hit the brake the pads were really close to the disc and made contact quicker than they were supposed to (with less caliper piston travel).  To test this, we ran the bike to about 20 MPH on the center stand, hit the rear brake to lock it up (clutch pulled), then spun the rear tire to feel for brake pad drag.  Then we ran the bike back to 20 MPH, pulled the clutch and stopped the tire with our shoe, then spun the rear tire to see if we could detect a difference.  We detected no difference.

Any ideas?

[ducati_nolan]

Check your pads, worn down pads can cause the brakes to lock up suddenly. Also check that your wheel is aligned and adjusted evenly. Also make sure you don't have any loose bolts. If all that is good, then you probally have a coroded or worn caliper. A fluid flush couldn't hurt and is cheap, so try that if nothing else works.

I bet it's the pads.