Brake Fluid Expanding?

[drhach]

I have a weird thing happening with my front brakes on my 78 GS1000. I was wondering if anyone here has seen this before.

When I roll the bike out of the garage, the brake lever has a ton of travel. After sitting in the sun for a few minutes, the travel starts to go away. There have been a couple of times where the brakes self-applied and locked up all together, I had to bleed off some fluid in order to get the bike to move. I can understand if the calipers are sticking that they will not return, but what is happening here is that the brakes actually apply themselves. They go from being loose to fully locked. It seems to happen when there are changes in temperature. I know normally when brake fluid gets hot, the brakes tend work worse. I know there is some air in my lines and that I need to replace my lines anyways. I am going to take care of that. I didn't think those things might cause this though. I've never seen self applying brakes before. All I can think is that it is a combination of things. Like maybe the return hole in the MC is clogged and the fluid is heating up. I don't know. Has anyone here ever encountered this before? It's new to me.

[Nessism]

Sounds like the air in the system is expanding and pushing out the fluid. Might be a good time to get those new lines and flush out the entire system.

[Steve]

Yes, I have encountered it and you have already identified the problem.

Clean the return hole in the master cylinder.

.

[drhach]

Thanks, guys. I suspected this was the case, and I knew this stuff needed to be replaced anyway. I'd just never seen this before.

[tfb]

Yep, those locking brakes can be pretty darn scary. Had an XJ550 Yam which got into the habit of locking the brakes; lotsa fun when you're in heavy traffic, let me tell you...