Just a guess but if the caliper was stuck it probably built up enough heat to fuse the pads to the rotor. Once the rotor got hot enough to glow red it expanded to the point of locking up the brakes.

 

Damn Motive, that sucks big time, thank heaven it wasn't at speed, and in dense traffic. Glad you're here to tell this.

There was a tale on the V-Rod forum long ago about the same phenomenon, it happened to whoever it was, at full highway speed.

The cause of the lockup is expected to be boiling of the brake fluid, pressure in the line having the same effect of clamping the brakes, because the return fluid vent hole was covered.

The cause earlier, as I recall was presumed to be installation of brand K "multi-fit" custom brake and clutch levers that did not "multi-fit" very well.

The prior victim of this occurrence was on the way home from having said "multi-fit" custom brake and clutch levers installed AT THE DEALERSHIP!

As I recall, whoever this was, duplicated this on a dyno, turned out the poor fit of the lever kept the handle from being all the way released,

and when the handle is about a half inch from being all the way released, the piston covers a return vent hole, sealing the hydraulic system to the building back-pressure.

Murphy's Law perfect set of horrible circumstances. if the return/vent hole was not covered, brake fluid would not be boiling,

but if it was for some reason, the boiling fluid pressure would just bubble back and overflow the reservoir.

...

 

The cause of the lockup is expected to be boiling of the brake fluid, pressure in the line having the same effect of clamping the brakes, because the return fluid vent hole was covered.

...
and when the handle is about a half inch from being all the way released, the piston covers a return vent hole, sealing the hydraulic system to the building back-pressure.

Murphy's Law perfect set of horrible circumstances. if the return/vent hole was not covered, brake fluid would not be boiling,

but if it was for some reason, the boiling fluid pressure would just bubble back and overflow the reservoir.

...

Thanks,

Nathang, as odd as it sounds, that actually makes sense....

That explains why it happened once I got more than halfway to work, and why it released once I was ready to ride again....

I'll be digging into that once I get the bike home...it'll be down for a while anyway, since I've got to order some new parts for the ones that broke...including the rear bake lever...

 

Glad your okay and able to walk away from it.

 

Motive, I think Nathan is right on the money. Similar thing happened to me once. I was having trouble with my front brake light switch, so I modified my lever to make better contact. Well, it was also putting very slight pressure on the brake plunger, causing drag. The front brakes bound up and brought the bike to a stop, but not bad enough to put me down. I relieved the pressure and got home, and undid the mod. Never had another occurrence. I still think you're right to check the caliper pistons as well.

--

 

Makes more sense, since the harder I was trying to push the bike through it, by downshifting, the harder it started locking up, until the front tire lost grip and took a dive...

 

I've also seen a brake hose collapse( inside) no visible outside damage. And cause the same thing. The hose will pass fluid when pressure is put on it, but won't allow the fluid to release fully. Acts like a check valve. So if the brake lever isn't your problem, check the brake hose.

 

If your caliper piston was physically sticking, like from corrosion in the bore, there is no logical explanation to it releasing.

The puzzle is, was your brake lever stuck just slightly retracted, is there anything that could explain that?

In the case of the "multi-fit" lever, they knew there were some fit issue during install, and they tried to make some corrections,

but not enough apparently, and did not anticipate such drastic consequences..

...

 

The puzzle is, was your brake lever stuck just slightly retracted, is there anything that could explain that?



...

I'm using stock levers; however, like Silverback, I'd done some 'mods' to make better contact with my rear brake light switch....but I'd taken that off a while back, when the light started behaving the opposite way than it's supposed to....(on when it's released and off when it's pulled)

Could be the tight fit I have with my aftermarket bars and the hydraulic lines, but I've run with those bars for around 45k miles now...

 

One simple way to prevent something like this is to always check the release valve anytime you do any work on your brakes. With the cap off the reservoir, operate the brake lever and make sure the fluid burps every time you release it. If it doesn't you know the valve is either stuck or corroded and needs attention. Nathang's post is dead on. I hadn't thought of that until he pointed it out. It might not have had anything to do with mods to the brake system, although that could certainly be one explanation. Even an unmodified system can suffer the same fate. That's why it's so important to replace the fluid at regular intervals. It doesn't take much condensation inside the lines to cause something like this to happen.

 

I vote for a full flush of the master cylinder. My girl and I had a close call on our 2001 Harley Road King with stock brakes. We were stopped at a light and made a right turn onto the highway. As I shifted into 2nd gear, the front tire began to wobble (feeling almost like it was flat), and immediately after that, the front calipers engaged and locked up the front wheel. We managed to keep the bike upright and ultimately came to rest, skidding into the grass and dirt on the side of the road. The front brake was fully engaged and the brake lever would not budge. We stopped fast enough that we left a dent in the front fender as the front shocks went all of the way down 
The cause? Crap in the master cylinder that prevented the brake fluid from flowing freely through the system. Here is the explanation, paraphrased from another thread here on the forum;
“A hydraulic brake system is a closed system. When brake fluid expands with heat, the pressure bleeds back into the master cylinder at the handle bars via a very small hole at the bottom of the reservoir. If that hole is plugged or sealed over with crud and cannot escape into the master reservoir, then expanded fluid will press the caliper pistons onto the pads and squeeze the rotors. The result will be the front brake locking up…and a possible accident.
To see if the hole is plugged, pull the master cylinder cover, blip the brake lever, if you see an air bubble rise thru the fluid, the hole is unobstructed. No bubble? Pull the assembly apart and clean out that hole.”

 

Were you able to determine from blueing or some similar indicator if both rotors were red, or very hot?

Since the hydraulic lines are T-connected, pressure should be equalized, the fine logic of the scenario I'm suspecting would make likely, if not inevitable, that both disks are equally affected by the building back-pressure.

The other requirement is that somehow the pressure return hole in the brake master cylinder was blocked, or else no backpressure buildup seems possible.

I'm not really that familiar with the master cylinder construction, to have a good feel for when the return would be obstructed. Should be very soon after starting the pressure stroke.

..

 

I had the same thing happen to me on an older bike. The front rotor over-heated and I felt the front brake come on all on its own.
It locked up the wheel as I came to a stop on the side of the freeway. As soon as the rotor cooled, it became free again.
It turned out to be the master cylinder. The master cylinder/piston was corroded and got stuck, with light pressure pressure on the rotor. The light pressure was enough to eventually over-heat the rotor as I rode, causing it to lock up. I was real lucky that I was able to pull over off the freeway before it finally locked up.

Lesson learned for me; check and change your brake fluid as recommended!

 

Yeah, both rotors show blueing.

Thanks to everyone for the insight and advice, much appreciated. I'll be digging into the brake system soon, once I get some replacement parts in for the broken stuff..