Here's the deal. I didn't think I would write this one up, but again I found the Kawasaki and Clymer manuals lacking. The 1500 Classic went from a single piston rear brake caliper to a dual piston rear caliper in 2001(E4). None of the manual for a Carb'ed 1500 Classic even note the change. Hence the need for my post.
Here's a exploded parts view. (Those aren't full part numbers only prefixes.)
Time to get down to business. The manual(s) tell you to take of the exhaust, but I don't think you have to, even with a stock exhaust system. I thought about moving my saddlebag support out of the way for clarity, but it's not hard to work around. If you can get to the two socket head screws then you can do the job.
Take these two bolts out.
Slide the caliper off the rotor.
I tried to clean everything, but it really didn't do much.
Here's the pin(92043) that hold everything together. This pin had another pin that holds it in place. The stock one is a tiny re-useable cotter pin, but that is long gone. I have been using standard cotter pins. Safety wire would work fine, too.
Whatever you got pull it out.
Then the big pin.
Inboard pad rolls over and slides off the other pin.
Outboard pad pretty much falls out.
If you didn't top off the reservoir when the pad were already worn out, then you should be able to squeeze the pistons back in with a c-clamp with any issues.
That's bottomed out.
Fresh pads. DO NOT BUY THE GOLDEN LOOKING ONES. Those will wear longer, but if you're lightly trail braking they are loud and scary sounding. I took a pair of those off after a like a thousand miles.
Pick out a new cotter pin.
Cut it to a useable length.
Drop the inboard pad on.
Install the outboard pad. Slide and turn.
Install and bend cotter pin.
Slide caliper onto rotor.
Align and install bolts.
Torque to 25 ft*lb.
Pump up the rear brakes and make sure they work.
Put up your tools.