I recently purchased a 2000 Sportster XL883C and have the following experience. During a ride, after about 15-20 minutes, the rear brake begins to lock. No application of the brake petal. Some have told me it is a collapsed brake line, some have said it is an air lock, some have said the caliper is bad. Any of you experience the same issue and what was the cause?

 

Do you mean you have not applied the rear brake during the ride at all or the they start dragging after 15 min and you have used the rear brake a couple times?

 

Not applying the brake at all. Feet up on the highway pegs.

 

Flush the fluid with new. Typically this is caused by water absorption into the fluid. It happens frequently. The water gets hot, expands, applies brake.

 

completely flush the line and you should be good to go .

 

wrong, the caliper is sticking, flushing will not clean the pistons in the caliper.
pull the calipers( both ) disassemble and clean/replace the pistons. they are sticking in the bore.
then flush the system

they are not allowing the pads to break loose from the disc. because they cannot move into the caliper as pads swell from heat
result=pads get hot then expand and lock or try to lock the brake because the pistons cannot move back.
Have seen brakes lock up because of this and throw the rider, not good ending .
hope this helps

 

Yep....had to rebuild my calipers when i first got the bike (previous owner let it sit for some time). Not a big deal to do and awesome brakes when your done.

 

Thanks Mike - Your wisdom was much appreciated - that corrected the problem.