ft calipers locked on highway w/out touching them!

70mph cruisin, down to 60, open up throttle, 'whats goin on? are the rings crappin out?'
down to 50, 40, no exits, NOOOOOOOO
keep it at 40 open throttle for 3/4 mile, get off exit, pull clutch to coast down downramp and the front end takes wicked dive and the bike revs High, whew, not the motor.

Can't roll the bike of course, hangin off shoulder and the front wheel is up in smoke

luckily i made a small tool kit from some other japanese bike tool kit and pouch and put it on my XJ

10 mins later, opened up the banjo on the left front, some fluid squirted, tightened it up and BAM they work. had a friend escort me home w/ his hazzards on and didn't use the front brake.

just broke everything down to the last part, including the window on the MC. there was no boot on the left caliper piston (but the circlip was there) and particles in the fluid from the calipers.

other than that they were ok. how the hell does that happen without touching them?

off to the parts catalog

 

There is always a little drag on disc brakes.

Going down the freeway that drag makes heat.

Heat causes brake fluid to expand.

Pressure due to expanding brake fluid should be relieved by that very tiny hole in the bottom of the master cylinder.

If that hole is plugged pressure pushes pistons out, creating more friction, creating more heat, creating more pressure, pushing pistons out more, creating more friction etc. until it either locks up or the engine can't push it any more.

 

thanks MiCarl, just looked at my MC, didn't find a hole on the underside of it (duuuuuu) so maybe it's one of the two in the bottom of the resevior. I always thought those two holes was to take pressure from the plunger and push it down the lines...
wherever it is, how can I really KNOW that it's clean?my guitar string or something substantial that I can see with my eyes. Thanks

 

That guitar string cleaning tool comes in might handy! The two holes in the reservoir are different, one is an obvious hole and the other looks like the drill bit didn't make it through the metal. That is where the small hole is, and what you need to clean out. Search for front brake drag.

I believe you are supposed to get a fountain coming out of that hole when you apply the brakes (with the reservoir cap off) if it is working properly.
You may want to check your rotors for warping, if you rode on the front brakes for too long, and consider replacing your pads too. This is why you must be able to TRUST YOUR BRAKES WITH YOUR LIFE!

 

i had that problem on a 65 magna i had couiple years back. i used a pin. like a sewing needle pin. the hole was filled with rust so it was easy to spot.

 

this isn't a yamaha mc but the idea is the same, the tiny hole in the middle
how will you know it's clean ?
your going to take it off take it all apart and clean the whole thing till it's as clean as a baby bottle, then you know it's clean