Clutch slave question

[macx]

I've been around the block about a dozen times with this darn clutch thing, thought it was bleeding, did every trick suggested.

I've bled it top down and bottom up, tilted the bike every which way, rapped on the banjo connection, fastened the clutch lever depressed overnite, used a regular bleeder and a speedy bleeder, a vacuum bleeder, etc etc etc, and run at least a couple quarts of fluid thru it.

Finally had enuf and took the slave out without disconnecting any hoses and after it had been bleed very very thoroughly.

I could hold the cylinder in with the clutch pushrod by hand while my wife pumped the clutch handle and could feel no hydraulic pressure from the master.

There are absolutely no leaks visible in the slave.

Is it still possible the slave is bad somehow? I read a post on another
forum about several experiences on GS1200's where that reportedly happened - the clutch "went away" over a number of miles and after rerouting hoses and repeated bleeding by dealers, the problem was solved by replacing the slave cyl's even tho there were no visible leaks.

I don't see where the hydraulic pressure could go if there's no leaks and the system is thoroughly bled, but - -? It still seems to me that there is insufficient pressure being generated by the master.

Any similar experiences or thoughts? I'm laid off and can't afford right now to be throwing significant amounts of cash at the problem to replace both the slave and rebuild the master or buy a lo miles used one just hoping somehow that'll solve it. I'd of course much prefer to know what the problem is so I don't waste money on unnecessary parts. And, hope against hope, finally solve this mystery and get that POC working and keep it working.

[CycleRob]

You need to take the master cylinder apart and closely inspect and clean the piston seals. You may have a chipped/torn/worn piston seal or a defect in the cylinder bore. While it's apart, insure the 2 cylinder feed/bleedback holes in the center of this pic in the reservoir are open and clean, especially the tiny one on the left in that pic. It's a very simple system, and unless 1 piston seal was removed and reinstalled backwards, it should be easy to find out why it's not working.

[macx]

I neglected to mention in this post that I've had the M cyl plunger & seals out. Both small holes were completely open (I had checked that while bleeding), a few small specs of black crud lurking in the bottom crevices of the reservoir which I thoroughly cleaned out, seals looked OK at least no cuts / tears etc and no obviously worn down edges. 1 tiny spec of something on the leading seal but not near the sealing edge.

Swabbed the bore out some, not real thoroughly, nothing came out on the swabs, not even any significant discoloration other than residual fluid dampening the swab.

Rather than take the whole mess apart and really get into the bore, I tried reassembling it and testing. Still not a bit of hydraulic pressure.

You'd think it would generate some noticeable hydraulic pressure.

Besides, the bike only has 32k on it. I bought it summer of 08 with 25k on it and being new to BMWs and having no idea of any previous service had the dealer bleed the brakes & clutch, and I've bled it a couple times since during a clutch change and later this past summer with some trans work (internal gear ratio change, did it my own self, even). So it isn't like fluid has been sitting in there any length of time at all.

It seemed to work fine with no noticeble problems from the time I bought
it until this past summer when awhile after my clutch change I seemed to notice it getting a little "weak", then it went downhill from there, with the rate of weaking increasing fairly rapidly until it wont' generate any pressure at all.

Next thing I'll try, given the relatively low miles, is to first do a more thorough look see and attempt at cleaning the bore, then install the
rebuild kit (basically plunger & spring) from the Boneyard. Without any leaks visible in the slave or the hoses & connections, that's the only thing remaining I can think to try.

[NoRRmad]

Does the brake lever come back all the way to the grip when you squeeze it? Slowly? Quickly? If not, I'd suspect an obstruction in the line; brake pressure is being developed at the master cylinder, but presses only against the clog, not the slave cylinder.

[macx]

Yup, afraid so. Limp as a noodle.

[NoRRmad]

Well, if it were the slave, there'd be a leak, even if you don't see one. Does the fluid level go down after a bunch of squeezes? If not, it's gotta be the master cylinder. I like CycleRob's theory about seals installed backwards, but could be internal scoring of the cylinder around the piston.

[macx]

Nope, fluid stays the same.

So, has to be the M cyl.

Ahhh, but a seal suddenly going backwards? Then how would it have
worked over several thousand miles from the time I bought it when
it hadn't been apart until after the problems started? Unless I've got
brake master cyinder gremlins messing with it in the middle of the night :-)

When I pulled the plunger out after it quit working the seals were
on the plunger correctly and I sure didn't turn them around when I
reassembled it to test it after checking & doing some cleaning.

Gotta be in the bore, just hope it's not scored so the rebuild kit will
fix it up. When the weather warms I'll do a close examination.

[CycleRob]

From the additional info that's been added it points to a bent lever or one that is now out of adjustment. Specifically, it's the blow-by clearance adjustment. That's the small threaded shaft recessed in the threaded hole in the lever itself with the red thread locking agent on it. A complete adjustment procedure is in section 32 on page 9 (32.9) of the CD manual in the STEERING section. It can happen either thru a tip-over that minutely bent the lever -or- corrosion/crud buildup affecting the sensitive adjustment. That means the lever is not fully releasing the master cylinder piston, preventing the piston seal from uncovering the tiny bleed hole so air can bleed up-n-out.

Normally that blow-by clearance adjustment is set only once at the factory, and needs to be reset if the lever is traumatized or parts are replaced. When it's adjusted correctly, you should see tiny bubbles streaming from the tiny bleed hole (not the larger one) on every partial squeeze (just clicking the microswitch) of lever movement until it is fully bled.

[macx]

I'll check that - anything is worth taking a look at.

However, I've never tipped the bike and the system worked fine
for all the ~7,000 miles I've put on it, and when I disassembled
the MC I checked and the adjustment seemed to be firmly secured,
not loose so it shouldn't have slipped. Also the parts, incl that portion,
did not have any discernible crud build up.

During my numerous bleeding attempts, I have determined
that the small bleed hole was being uncovered so it doesn't
appear that the plunger is insufficiently retracting.

Question, though - if all air is successfully bled out of the system
why would air bubbles come up thru that hole every time the
lever is released - where would the air be coming from? If the
holes are covered with fluid from proper fluid level in the reservoir,
no air should be induced when the lever is operated.

Nothing like a mystery to induce one to research and learn the minute
details of how something is designed to function!

[Boxer]

Question, though - if all air is successfully bled out of the system
why would air bubbles come up thru that hole every time the
lever is released - where would the air be coming from?

Macx, he's talking about bleeding it after a component replacement/removal. Once all the air is bled out properly, no air bubbles should be seen coming up unless you have some leaking in somewhere.

I would have guessed you may have your slave cylinder fluid line connections attached improperly, except you stated earlier that you didn't disconnect them when you removed the slave. I think your slave is bad. This is a puzzler.

[BigJohn]

I don't know specifically about an 1150 master cylinder, but on most types you can test the master by disconnecting the flex line from it and replacing the banjo bolt with a bleeder. Usually the threads are the same (10X1.00?) and you can bleed the master and it should get a very hard to pull lever. This will tell you if the problem is there or with the line and slave. Cover the area with a trash bag and some old towels to catch stray brake fluid, but you know that! If the master bleeds hard, it's good. I would then crack open the bleeder and pull the lever half way and put a tie wrap around it to hold the fluid in the reservoir and reattach the flex line and try bleeding at the slave. Don't let the fluid level drop low.

[macx]

Question, though - if all air is successfully bled out of the system
why would air bubbles come up thru that hole every time the
lever is released - where would the air be coming from?

Macx, he's talking about bleeding it after a component replacement/removal. Once all the air is bled out properly, no air bubbles should be seen coming up unless you have some leaking in somewhere.

I would have guessed you may have your slave cylinder fluid line connections attached improperly, except you stated earlier that you didn't disconnect them when you removed the slave. I think your slave is bad. This is a puzzler.

A puzzler, indeed! Story of my life, if there's 1 item out of many made that's bad and that doesn't work, guess who will have it?

Back to the slave - if it's "bad" would it not be leaking, andwould I not see fluid coming out if is leaking, and where would the pressure go that is developed by the master when the lever is pulled if it's not pushing fluid out in a leak? Remember I tested that by holding the slave piston in with the clutch pushrod while my wife squeezed the lever (after a very thorough bleeding) and I could feel no hydraulic pressure at all. And I removed it, tested it , and reinstalled it all without disconnecting any lines. Also, it still won't release the clutch.

Either there's something wrong inside the master bore, or I've just got "one of those" that's a particularly stubborn bleed. I'll check the bore out more thoroughly when it warms up, and if the bore looks good I'll try the rebuild kit. But I'll try a dab more bleeding before I spend any more $ on it without knowing for sure what the problem is. Maybe after sitting several months over winter any air that may still be trapped in the system will rise and can be released out of the small hole by working the lever.

Makes one long for the "good old days" when all one had to do was occasionally adjust the clutch cable a turn or so.