85 250R , Why do my front brakes lock up after 15 mins of hard riding

[whyzee]

why do they do this guys??? I have changed the entire setup to a new one I bought, and it's doing the same thing. Although I did reuse the master cylinder because I couldn't get the new one to make bubbles when trying to bleed it.
I have been bleeding the brake for days, but once it get hot from use, it expands and the caliper locks. Like I said it is a new caliper. Is it air in my system, or a faulty master cylinder? I have a crummy brake bleeder, the big syringe where you inject the brake fluid from below. I just cant get enough force to overcome the pressure without the little syringe hose blowing off the bleeding zuryk...ughhh!!!
Any Help is greatly appreciated!!!!

[RoscoW]

Without touching the brake lever can you get the syringe to pull fluid from the reservoir out thru the bleeder? My guess would be a master cylinder issue, when the lever is out fluid should be able to expand (When heated) back up into the master cylinder reservoir without blockage, sounds like yours is expanding with the heat and building pressure instead. Maybe time for a master cylinder rebuild.

Ross..

[Xowner]

might be the hose swelled shut and not allowing the fluid to return to the master cylinder

[Jason Hall]

Is the rotor bent? Or could It be the slide pins are seized up on both calipar's?

[NewfieBish]

i think you should try a new hose first.. sounds like the hose is collapsin or somethin

[whyzee]

cool, good thoughts guys. I just switched to a brand new master cylinder that I know works ( fyi, a 2006 suzuki rm250 master cylinder fits, hose and all, lever is just a little odd)
I was able to push some fluid up from the bottom, but not enough to get all the air out, so I have been manually bleeding for the past hour. They are almost good.
Now lets see what happens tomorrow when I ride. NO WAY should they expand closed this time.

Thanks

[whyzee]

Without touching the brake lever can you get the syringe to pull fluid from the reservoir out thru the bleeder? My guess would be a master cylinder issue, when the lever is out fluid should be able to expand (When heated) back up into the master cylinder reservoir without blockage, sounds like yours is expanding with the heat and building pressure instead. Maybe time for a master cylinder rebuild.

Ross..

no !!! I think you are dead on right! i put a new master cylinder in. will lets you know tom.
Thanks