Front brakes continue to Slowly lock up. ABS?

[VashonKbike]

I recently got a 96 K1100 with 17K miles.  It had been sitting for about a year and the front master cylinder was just rebuilt by the previous owner. 

I'm having strange issue where over a period of time, maybe 5/10 miles of riding (it varies due to how much front brake I use)  the front brakes will slowly become firmer and firmer until eventually the pads start to drag and then a few pumps more and they will completely lock up.  Then I'll have to bleed some fluid out of the front calipers to free them up.  The process will start again.  is this an ABS issue?  Air bubbles in the sensor? Something with the master cylinder?

I was having some ABS error alternate flashing lights previously but that went away when I swapped out for a new battery.  Now all the ABS lights act correctly.  Flashing simultaneously and them going off after I hit 2.5 MPH.

I've bled the fluid, replaced the battery, reset the ABS, but still having the issue. I'm no master mechanic, still in my early stages of learning.  My other bike is an airhead from the 70's so ABS is all new to me.

Any advice appreciated, thanks!

[johnny]

greetings vashonkbike...

welcome to motobrick.com...

im thinking they gotts the piston in too far when they did the master rebuild... will operate enough to brake on the lever pull... butts not enough to equalize the pressure on the lever release... in other words... your piston is whack...

j o

[Inge K.]

Or the piston doesn't return fully, it should no free play between the lever and piston.

[VashonKbike]

Thank you, so it sounds like plumbing in the master cylinder more than some kind of ABS issue. 

Is attempting to re-seat the piston beyond an intermediate task?  Wondering if I should attempt it myself or get it to a shop?  I live on an island, so it's much easier if I can do it myself.  But Seattle's not too far away.

[Inge K.]

What's usually prevents the piston to return fully is corrosion and crystalized brake fluid in the outer end
of the bore...you need to remove this from the bore, and first remove the piston which then of corse
can be tricky.

A sign that this is the problem is that you have play between the lever and the piston, but it could also
be wrong adjusted by a PO and then have zero free play.

Johnny have made a how to dismantle the master, I think you find it in the Lieberry.

[johnny]

yawl... its in the lieberry...

could mail order another kit...

could take it to vallantine and let him mess with it...

butts i would make sure your fluid is running clear with no tiny rubber pieces in there... both at the abs modulators and at the calipers... bleed abs modulators 1st then the calipers 2nd...

j o

[VashonKbike]

Johnny, thanks for the link, that definitely makes the process clear!  I may open it up myself. 

[Scott_]

How old are the brake lines. Not uncommon for old lines to start de-laminating internally and act like a one-way check valve.

[VashonKbike]

Scott, I'm guessing they are original from 96?  Is it time for Spiegler?

[Scott_]

One way to find out if it's the lines or not, the next time they start to lock up, loosen the banjo bolt at the master cyl and see if you can bleed off the pressure to release the brakes. If yes, then your problem is not in the lines, if not, you most likely have a line issue, and time to replace them.
Just be careful of brake fluid on the paint, not compatible........ :yow

There could be a very remote potential of the ABS controller causing you an issue(only because it is in the brake circuit), but I can't say as I have heard of anyone with your same symptoms finding the problem in the ABS. It's usually been in the MC or lines.

[VashonKbike]

Thanks Scott, I'll give it a try! Haven't had much time to play with it lately.

- john