Help, front brake problems.

[Saculia]

I have a 1993 gs500e that I have loved, and riden over 40000 miles.  Yesterday, I took the bike for a ride, and all of the sudden my front brake lever began to stiffen up.  Pressure was being applied to the front brake caliper without me applying any pressure to the lever.  I initially thought that maybe the brake fluid was too much, and there might have been an air buble previously, that had now escaped.  I pulled over, and releaved the pressure by removing some brake fluid through the bleeding screw on the caliper.  The front weel started spinning freely.  I rode the bike a little bit, but after several brake applications, the same problem occured.  I stopped and releaved some more pressure by draining more brake fluid throught he bleeding screw.  I rode again, and the same problem happened again. 
What could be causing this?  I don't think that there is anything wrong with the calliper, because once I releave the pressure through the bleeding screw, averything works.  Could there be something that is preventing fluid from returning to the brake master cylinder after the brake has been applied? 
Any help would be greatly appreciated.
Thank you in advance,
Anatoly

[makenzie71]

Thats one of the craziest things I've ever heard.

How longs it been since you've drained and replaced all the fluid?

[scratch]

Flush out the old brake fluid, it's holding water!  The current brake fluid has absorbed enough water to lower it's boiling point.  Right now, when it heats up, it expands, actuating your brake pistons without you doin' a thing (but riding) and locks up the front.  I've had this happen on a group ride, a guy on his 900SS Ducati started braking in the middle of a turn for no apparent reason (I was the sweep), same thing happened to him.  Luckily, I was there with tools.  This is why it's so important to change your brake fluid every two years!

[Saculia]

Thank you very much for your suggestions.   It has been about 3 years since I changed the brake fluid in it.

[manofthefield]

It's also possible that there is some kind of blockage in the master cylinder or one of the passages, though it probably is just water.

Sounds like have it under control, but Make sure you don't ride until it's fixed.  I had this happen while I was test riding my dad's freshly restored Suzuki RE-5.  The brake got tighter and tighter as I rode (1 or 2 miles) until I got home and hit some sand at the end of the driveway and the front slid out from under me.  Scraped my knee and did a few hundred dollars damage on a collectors bike because my dad and I didn't do a good enough job cleaning the front brake system out.

[budget speed demon]

not that its causing your problem but be aware of the differences between 'dot 4' and 'dot 5' brake fluid.

[makenzie71]

Flush out the old brake fluid, it's holding water!  The current brake fluid has absorbed enough water to lower it's boiling point.  Right now, when it heats up, it expands, actuating your brake pistons without you doin' a thing (but riding) and locks up the front.  I've had this happen on a group ride, a guy on his 900SS Ducati started braking in the middle of a turn for no apparent reason (I was the sweep), same thing happened to him.  Luckily, I was there with tools.  This is why it's so important to change your brake fluid every two years!

Good call!  Only thing that could be the culprit, really.

[Blueknyt]

a more drastic case is the line deteriorating and little crude blocking the return port in the master cyl.  this is rare. im more inclined to go with Flushing the system