1986 front disc brake problem

[straughn]

After riding my 1986 KDX 200 for a half hour or so in the woods the front disc brake gets tighter and tighter until it locks up. I bleed a little fluid out and it works great for a while longer and then gets tighter and tighter again. Does any have any ideas ? Thanks

 

[julien_d]

MC rebuild?

 

[dirt bike dave]

Do you have too much brake fluid in there?

If the system is overfilled, when the fluid gets hot and expands, it has nowhere to go except to activate the brake.

BTW, if you do some work in your brakes and decide to replace the fluid, Motul 600 is an outstanding brake fluid with a very high boiling point. It's worth paying a little extra for, IMO.

 

[Dirtdame]

And it expands even more if it's contaminated.

 

[ellandoh]

sticky caliper causing an overheating condition

 

[Joburble]

I have heard that air in the line will cause this. The reason is that as you use the brakes it all gets warm and the air expands pushing the brakes on, then the more the brake is on, the worse it gets. I have no experience with this, it's just something I heard or read somewhere.

 

[Matt90GT]

2 reasons

#1 you have dirt between the lever and the contact point of the master cylinder causing it to keep pressure on.

#2 you have a sticking piston in the caliper. Thus buy a rebuild kit and fix it. .

More than likely #1. There has to be a gap between the lever and master cylinder plunger at all times. If not, that is your cause. This can also happen when you use a lever not designed for the mastercylinder

 

[mudpack]

First thing to do:
flush the old fluid with new, bleeding all the air out in the process.
If that doesn't cure it, take the master cylinder apart and check it.

"I bleed a little fluid out and it works great for a while longer"....doesn't sound like a sticky caliper piston to me.