LS caliper issues

[flatlander]

Hello, I am having a strange issue with the Brembo front brakes on my R65LS and wonder if anyone here could lend some insight? When I bought this bike the front calipers were sticky so I kitted them both including new pistons. At the same time I rebuilt the master cylinder and installed new pads. I test rode the bike about 25 miles to bed in the new pads and I put it up. It sat idle for about four months and when I got back to it the front wheel was dragging the pads to the extent that it was difficult to push. I vacuumed out the brake fluid and added new but the problem remained... so, I dismantled both calipers and the m/c, purged the lines with denatured alcohol and reassembled and it worked fine for a couple of days and then sat for another day. Today I pushed it off the stand and the calipers were clearly bound again. The rotors show light wear but virtually no runout. The pistons are not sticking in the calipers but rather the whole system is somehow pressurizing itself and eliminating any free play that should exist at the lever. When the pistons are pushed back in the pots they do so readily and the fluid returns to the m/c without restriction. This is hardly my first brake job but this one has got the best of me... anybody have any ideas short of throw new parts at it? Thanks for your time!

[Bob_Roller]

Inside the master cylinder resevoir, there is a bleed port, looks like a small conical depression, there is a very small hole there, make sure it is open, put a small diameter wire in there to clear it out.

[flatlander]

Roller_Bob, Thanks for your speedy reply. Unfortunately it is not the bleed port as this was my initial thought as well. I have pushed fluid backwards through the system with a large syringe and it comes back out the port unimpeded... I can push the pistons back easily with my thumbs and the fluid goes right back in the m/c like it should. Great guess but that's not it. This one truly has me perplexed...

[Bob_Roller]

Another outside possibility, is where the bolts that secure the caliper to the fork leg, have 'hat' or flanged bushings in the fork legs to center the calipers on the rotor.

There are different thickness flanges to adjust the caliper alignment.

A real wild guess here, mind you !!!

[flatlander]

Wild guess or not your response is much appreciated! When I did the original rebuild on the front calipers I discovered the right caliper lived a bit inboard to be centered over the rotor so I lapped the bushings down about .030 or .040 to center up the disc... worked perfect! So no, it's not the bushings... but once again, that is an excellent point. Thanks!

[Bob_Roller]

At this point, I'm out of useful, and useless information about this !!!

[flatlander]

Bob_Roller, Thee and me sir... I appreciate your efforts just the same! thanks..

[Crossrodes]

What condition are your brake lines in?  I have heard of lines getting so bad that material flakes off into the system.  This could be causing some problems.

[flatlander]

Crossrodes, Externally the lines appear as new; internally I guess I'd need like a mini borescope or something to see in there in any more detail. I did have every single part including the lines on my bench and I could see light through them so no major artery hardening. I have vacuum purged/douched/refilled this system repeatedly now and the fluid is clean clean every time... if there is anything but dot 4 in there I would be stunned. Pretty good observation on your part - the right flake of rubber could easily plug the return port and act like a check valve. I wish it was that but no such luck...

[Justin B.]

I had an old BMW 1600 (car) once that was giving me clutch actuation fits and it turned out to be the hose collapsing internally.  Of course, I only discovered that after rebuilding the master cylinder and installing a new slave cylinder...  

[scuba]

Just a wild guess. Some years ago something similar happened due to worn out rubber hose and brake fluid reminded under pressure since it was hard for it to go back (upwards). Another wild guess is that something is keeping master cylinder under pressure (clogging it). Make sure that there is no air inside master cylinder by pressing it slightly while container is opened and look for air bubbles. Pressing pistons by finger is enough to push fluid back but pads don’t have fingers and therefore even small pressure inside the system can keep them forced against the rotor/s.
Check the master cylinder and rubber hose first

[MrRiden]

W.A.G. method says look for wear ridge in the master cyl bore that causes the piston to settle where it's use to, not where it should be now with new pads. Also the hoses may be clean but delminated causing an internal buldge / blockage.
rich
checkin' the Vegas odds on this.

[Rob Valdez 79 R65]

If you don't know the age of the brake lines, you probably should have included them in your rebuild, anyway (I did).

I am so anal, I even replaced the metal pipe bits.

[flatlander]

Hello,

First off, thanks to all who replied to my posts and secondly my apologies for my delayed reply.

Justin - as it turns out the hoses are next on my list... forty continuous years of wrench now it seems I would have encountered this prior and perhaps this explains my reluctance to buy into the hole internally collapsed hose theory... that said, it may just be the solution. I also once owned a 2002 tii that was a handful to keep together but then I guess the car stuff is a whole 'nother story!

Scuba - As for the rubber hoses please see above. I realize that calipers don't have fingers... my point was that the calipers are not sticking. I believe it is common practice for people to pry back the pistons by a variety of means - c-clamps and so forth. In fact I have a tool that is designed for just such purpose - kind of backwards acting pliers if you will. The snap-on man got about fifty of my hard earned dollars years ago and as a result I can retract the piston in any caliper with professional aplomb! My point was that the piston to caliper bore interface is so smooth that my thumbs alone are enough to press the pistons home. I would have to disagree about the small pressure theory... once the lever is released ANY pressure large or small should be relieved into the m/c reservoir - unless there is an obstruction. I do hope the hoses are the culprit as it would explain it all...

McRiden - Gotta love the WAG method! I'm serious... anything but replace 1,000 dollars worth of stuff to cure an undiagnosed issue. As certain as I am that the m/c is fine I will check the bore for issues and be sure the piston returns as designed. Again, please see above for my take on the hoses... while I hate like hell to admit it, this delaminating thing kinda makes more and more sense. I dunno what the Vegas odds are but I wouldn't bet against your theory!

Rob Valdez - I'm thinking you guys are dead on with the hose issues and it's a tough admission for an old guy who actually thinks he may have almost seen it all! Nevertheless, something IS wrong and if it is not the calipers and it is not the master cylinder or rotors what's left? I assure you I understand and appreciate a job, any job, done right and would never confuse such with being anal!

Since I last posted I have completely R+R'ed the entire system and it seemed fine so I cautiously rode it about 2 or 3 miles without incident - I thought it was cured though I was unclear what fixed it. While this kind of fix doesn't inspire confidence I was content to accept it and tentatively ride the thing a bit. Tonight I decided to take it out and I could barely roll it off the lift... like an invisible demon the whole system is pressurized again... unbelievable. So... desperate to resolve this thing I came back here to see if anyone had further suggestion and the consensus seems to be the hoses. I pulled my file on this bike and the two lower hoses were replaced in December 06 - or at least the previous owners receipt says they were replaced in 12-06. I guess that leaves the uppermost little hose between the m/c and the splitter or junction or bifurcator or whatever the Germans call the block where all three hoses converge. One cannot really visually inspect the inside of this short hose as easily as the other two in that one of the fittings is a banjo type which prevents a straight through view. I'm thinking if it is a hose, it's this one.

Fortunately, I do have another LS that I can swap parts around so maybe I'll get it diagnosed and FIXED. My other bike is earlier and has ATE calipers but otherwise seems the perfect candidate for my tradeout scheme. I genuinely appreciate everyones help and will advise when I finally get this resolved...

[Justin B.]

We all will seriously want to know what the issue turns out to be!