Why is the rear brake locking up on my 1983 Virago 920 motorcycle? Just that. its locking up.
does it do this when you apply the brake. Does it lock up when you shift Any thing else you want to tell us. Maybe the brake shoe needs replaced. They do wear out.
The most probabe cause is a lack of lubrication and/or corrosion in the linkage from the pedal to the brake shoes, or in the shoes themselves. Easy to tell: With the bike on the sidestand, manually push the brake pedal and observe the linkage. If it appears stiff, take it off and see if it moves freely. My guess would be that you will have to take the rear wheel off and see what your brake shoes look like. May just need to carefully lube the springs and pivot points. One thing in your favor is that this is one of the simplest motorcycle braking systems around, and the rear wheel comes off easily. Chilton or Haynes manual is only $10-$15.
This can happen when either the cam or the shoes are worn past their limits. It allows the cam to rotate too far--almost 90 degrees, in some cases.