brakes lock up over night

[DogBunny]

My front brakes lock up over night. I can relieve the pressure at either bleeder -- just a very small amount of brake fluid escapes -- and then I'm usually good until the next day.

I am no stranger to master cylinders with plugged relief holes and to calipers with stuck pistons, but this seems different. I suspect that the original rubber hoses are swelling when I brake, and then contracting over night, causing fluid pressure to push on the caliper pistons.

Has anyone fixed this problem by replacing their brake lines? Year shouldn't matter, but it's a 1981 CB750C Custom.
Thanks.

 

[amc49]

That's impossible if that relief hole is open like it should be. M/C piston can drag to not return 100% back all the way too. Same thing. Bad brake hose can do it too when it collapses inside to then act like a check valve.

 

[DogBunny]

Thanks for the response.
I guess I was looking for a magic bullet, and hoped that new lines would be it.
What it probably really needs is for everything, both calipers and the MC, to be re-built.
Will be a while, but I'll report back with what I find.

 

[DogBunny]

Yesterday I finally got around to fixing this problem. Sure enough, the relief hole in the master cylinder was clogged.
So, it took zero dollars and about an hour to clean and rebuild the cylinder re-using the old parts to fix the problem.
What I don't understand is how the brakes worked at all with a clogged relief hole. I guess they were always dragging a bit, even when they were "working."

 

[amc49]

The brakes will still work with the hole 90% clogged and hole is so small that finally over one night it corroded enough to then close off completely.