Brakes Keep Binding Up??

[John451]

Well, this winter i changed my rm250 over to a steel braided brake line and at first it was squishy because there was a bubble in the master cylinder... Now after a while of riding the front brake locks up while the lever's out so i have to unscrew the bleeder screw.. Today i was so sick of it i just put a big bubble in the line. again this only happens after about 10 mins of riding. does anyone know why it was binding up and or how to fix it? Thank you

[wilkin250r]

I had a similar problem on a streetbike once. Best I can figure, there was water in the fluid.

When the brakes heat up, the water expands. It doesn't lock up completely, but it DOES cause pressure, which creates more friction, which creates more heat. More heat, more pressure, which creates more heat.

Brake fluid doesn't expand when it gets hot, but water does.

[John451]

Ohh, How would i get water in the line though? I mean i did use it for ice riding but i wasn't riding it with the cap off. But also wouldn't water make the brakes squishy? Because the brakes would tighten up as soon as you put your finger on the lever. I was thinking maybe it needs a new caliper or a rebuild.

[Young_Gun1]

when was the last time you greased the slides

[John451]

Greased the whatt? Does that answer it? I got the bike last fall and it's a 1997.. are the slides the pistons or the plate and pegs the whole caliper rides on? Because if it is the second one, when the brakes are working i can hit them and they'll apply and illl release and they'll release but while im just going they'll tighten up and eventuallly lock up and not let go, even while its sitting. I rolled it into my shed and i went out there and they were locked up so i unscrewed the valve and they released.. im thinking i may need a new master cylinder?

[Young_Gun1]

ok i have no clue then

[John451]

same here.. i think im going to take the caliper off, wind the pistons all the way in maybe spray something in it, and wind the screw on the lever all the way out because theres no play in it.

[wilkin250r]

When your brakes are locked up, and you unscrew the bleeder, what happens? It squirts, right? It relieves pressure? Are the brakes hot when this happens?

[John451]

Yeah the brake fluid squirts out, i havent had time lately to look at it but i think it is the lever because the adjuster screw is all the way in and i think its keeping it from enabling the pressure release section of the pump.

[wilkin250r]

And the brakes are hot when this happens, right?

So think about this. The reason your brake fluid squirts out is because it's under pressure, but brake fluid isn't supposed to do that. It doesn't expand like that when it gets hot.

So that can only mean that you have something ELSE in there, something that DOES expand when it gets hot, something building pressure as it heats up.


Your first thoughts are going to be "That's impossible, how would it get in there?" I don't have that answer for you, I don't know all the history. But I DO know that symptoms don't lie. Brake fluid doesn't expand like that, it's specifically designed not to. So the only other possibility is that you have something else in there that is not brake fluid.

By all means, fix the adjuster screw, but then change the brake fluid in the whole system. Use brake fluid from a brand-new never opened container. It should fix it, if it doesn't, then you need to go further with a complete system rebuild.

[John451]

yeah, sounds like that's it, i'll give it a shot tonight.