I don't know if anyone said this, but since the OP was asking what might be causing the easy rear lock up, if you were braking both at the same time, isn't it possible that one thing that could contribute to varying degrees of rear lock up on different bikes be what kind of pressure are in the front shocks?

I think I've read somewhere, and experienced myself, that if there's a lot of front shock dip from soft shocks, the temporary side effect is a lighter rear end, subsequently making it easier to lock up the rear wheel if too much pressure is applied at the wrong time. Not to say this is the case here, just thinking out loud that for some, if they've experienced stiffer front shocks vs softer front shocks, on a similar bike, it could affect how well they are able to implement the rear brake w/out locking it up.

I just bought a new to me 03 RKC and I think the front shocks are way too soft and this concerns me, plan on taking it in for a look-see...

 

gotta say..when I got my 06EGC i had to get used to those brakes, front and rear..bike before that had drum brakes front and rear ...yeah an old bike..71 flh still have it,,so imagine my reaction the first time I stomped on brakes on new bike....now...I can stop the dresser fast enough to make my eyes pop out...no skidding..wow a pun...just take some time and learn your bikes dynamics..every bike IS different..the statement about weight shifting to front is very true..it`s a heavy bike..the trick...be aware.

 

Done right, lightly covering the rear brake, and letting the wieght distribution from the front braking assert the pressure to the rear is the fastest way to stop that I have found, without locking. I was taught by a motorcycle LEO instructor. He made us practice fast stops by just allowing the force of movement to apply the rear brake. NO EXTRA PRESSURE from the rider. Your momentum from applying the front will force your foot onto the rear with the correct pressure.

I practice this technique with EVERY stop I make, so that it is an automatic response. I don't even think about it anymore, its become natural. And each spring, I hit a parking lot for 3-4 hours practicing stops, and panic stops, just to make sure my skills are where they belong for safe riding.

The other important thing that he taught us, was to ALWAYS look ahead as far as possible so you can be better prepared and not have to panic stop in most situations. If your head ain't on straight, LEAVE THE BIKE AT HOME! You become a danger to yourself, and everyone else on the road.

Concentration on a bike is critical to your personal safety, paying attention to your surroundings, and whats coming up, will make you far safer than you can imagine.

 

I"m from the old school of riding and its very hard to overcome the "rear brake first" instinct. I've locked-em up too many times BUT when you 1st notice your rear is sliding you can let off the rear brake provided you have the fronts gripping tightly. If you wait too long to let off, you're in for trouble.

So, do the ABS brakes really offer a safer stop?
I've heard opposite opinions but if it will help me over the old school of rear 1st, then I'll be heading to the dealer to get a new bike.

 

I think that is what I just said...