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Clutch Slave Help!

As I slowly reassemble the bike after replacing the transmission input shaft & clutch disc, I've run into a never-ending series of opportunities to spend money and learn how to fix more things.

Today's lesson was replacing the clutch line with a braided line from Spiegler. (The slave end uses an M6 banjo & bolt, which Galfer doesn't have. Spiegler has the banjo fitting, but no bolt.)

The old fitting was nasty rusty -- there's a neoprene cover over the hose, which apparently caused water to collect over the fitting:


New line looks great:


Except for one small thing...the bottom crush washer leaks. And not just a little bit. Brake fluid just runs out there, hardly any pressure goes to release the clutch.

I put on fresh crush washers, exact same problem.

The Speigler banjo fitting is thicker than OEM, but the banjo bolt is long enough that there's a good 5-6 threads screwed into the slave cylinder. I don't see what could possibly be causing this problem. The banjo fitting surfaces are smooth, the slave cylinder surface is clean, and the top crush washer doesn't leak at all.

I'm going to try tapping a plain aluminum block to M6 and connect the new clutch line to that. It should feel like a perfectly-bled brake at the lever, and no leaking. I'm suspecting that it'll still leak, though, which I think points to the banjo fitting.

If anybody has encountered this problem, I'd appreciate any ideas you have.

I hate hydraulics. Nasty, oily stuff.

Old 05-16-2020, 07:12 PM
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Hydraulics are nothing to be frightened of.

Parallel surfaces and a proper malleable aluminum crush washer with apropos tensile load (spec torque) will seal with nary an issue.

Distortion of the mating components from over tightening is a possibility in this case.

J.S.
Old 05-16-2020, 08:38 PM
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It might be the angle, but in the photo, the bottom banjo crush washer looks thinner than the top crush washer.
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Old 05-16-2020, 11:01 PM
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I've had only one memorable issue with a banjo fitting decades ago and that was on an older 6.9 MBZ with an CIS injection system The fuel distributor had a wonky mating surface which could not be serviced. No parts were readily available and the customer was a VIP - time was a factor. I ended up *annealing a copper washer. Nipped it in the bud.

* To anneal them properly you need to dunk them into water while they're hot (torch). If you let them cool on their own they temper and harden up again.

J.S.
Old 05-17-2020, 12:09 AM
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I'm with Jozef, go with annealed copper washers & clean the surface of the slave & check for even flatness, nicks etc. You shouldn't have to gorilla tighten it to stop it leaking.
Old 05-17-2020, 06:30 AM
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Is the old washer stuck in there somewhere?
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Old 05-17-2020, 09:38 AM
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I faced, drilled and tapped a plain aluminum block and bolted the clutch line to it using the banjo bolt...it didn't leak and held pressure like a champ. (This is with some copper Harbor Freight washers that I annealed per @Jozef Schumann's message.)

So I annealed a couple more washers and bolted the banjo back to the slave, and ... it leaks like crazy. In fact, I let it sit for a while and it leaked just from the pressure of the master reservoir being above the slave.

I don't see how this can happen -- banjo faces are fine, I checked the slave face carefully (it looks good), and the clutch worked OK with the old rusty OEM line a couple of months ago when my input shaft went bad. Maybe a flaw in the clutch body, which somehow gets plugged when the banjo bolt screws in a couple mm more than with the Spiegler banjo (which is a bit thicker than OEM)?

I don't especially want to buy a new clutch slave cylinder, but I'm not sure what else to do.
Old 05-17-2020, 11:19 PM
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I'm not there for a look-see, however, whatever is going on should be simple enough to diagnose. Particularly if gravity alone is enough for fluid to breach a seal.

"it leaks like crazy. In fact, I let it sit for a while and it leaked just from the pressure of the master reservoir being above the slave."

also, there's this:

"banjo bolt screws in a couple mm more than with the Spiegler banjo (which is a bit thicker than OEM)?"

Something is not adding up here. How can the banjo bolt be screwed in a couple mm more if indeed the Spiegler banjo is thicker? A thicker than OEM banjo would result in less service depth of the bolt (bolt will not screw into the slave deeper/more if the banjo is thicker). Are you certain the bolt is within its grip range and not bottoming out preventing any possibility of a clamp load?

This could very well be your problem.
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Last edited by Jozef Schumann; 05-18-2020 at 01:28 AM.. Reason: added info
Old 05-17-2020, 11:52 PM
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Quote:
Originally Posted by Jozef Schumann View Post
Something is not adding up here. How can the banjo bolt be screwed in a couple mm more if indeed the Spiegler banjo is thicker?
No, you're right...with the thicker Spiegler banjo fitting, the bolt goes into the slave body a couple mm less than with the OEM fitting.

What I was thinking is, maybe there's some flaw down at the bottom of the hole, and if you use the OEM fitting, the bolt screws in enough to plug it. (Yeah, I'm really reaching here -- what kind of flaw results in a channel from inside to outside without going past the bottom crush washer?)

I'm gonna take a much closer look at the bottom banjo to slave face junction. Maybe there's something keeping the banjo fitting cocked at an angle, or maybe the slave face isn't wide enough to seal across the whole banjo face.
Old 05-18-2020, 06:45 AM
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Post a photo of the two banjo fittings side by side showing the dimensional difference. If you have a digital caliper or precision ruler to actually measure the difference would be helpful as well.
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Old 05-18-2020, 08:22 AM
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If it were me, I'd replace they slave. Since you are in there anyway...and mine crapped out after 40,000 all on it's own. Actually probably crapped out at 30,000, but I kept nursing it along...very happy with the new fresh one, and it was not a lot of money (compared to the time it took to install it). https://www.beemerboneyard.com/21522335061n.html
I understand the impulse to save cash...but your time and aggravation is worth something, right?
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Old 05-18-2020, 08:26 AM
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Quote:
Originally Posted by mosearch View Post
I'd replace they slave.
Yeah, I'm headed that direction (I've heard the slaves go bad after a while, maybe the seals, but Beemer Boneyard doesn't have replacement seals any more. I really don't want to have to open this up again.) But I want to figure out why the new line isn't sealing, or I'll get a nice new slave cylinder and spew brake oil all over it from the same problem that I ought to be able to figure out now.
Old 05-18-2020, 09:00 AM
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Quote:
Originally Posted by spacewrench View Post
Yeah, I'm headed that direction (I've heard the slaves go bad after a while, maybe the seals, but Beemer Boneyard doesn't have replacement seals any more. I really don't want to have to open this up again.) But I want to figure out why the new line isn't sealing, or I'll get a nice new slave cylinder and spew brake oil all over it from the same problem that I *ought to be able to figure out now.
*this.

My '03 gets ridden by family, friends, and anyone who comes by wanting to go for a spirited sortie. I urge them to mercilessly flog it as if trying to kill it as long as they don't downshift over-rev. Why?

A long term evaluation of my clutch disc. Close to 50k miles have been logged on the most recent retrofit so far. I sincerely doubt anyone but the most hardcore owner who's routinely exersizing their machine on a track imposes such a severe duty cycle program.

Total miles accumulated so far:



BTW. all with the original hydraulics, both brake and clutch.

To the OP.

I took a gander at a clutch slave I have on hand.



Depth of the hole is more than enough to accommodate the bolt.

I was curious to determine if the components could possibly be of the 'NPT' variety. Very doubtful, but curious nonetheless. It is not. For your, and others (who may not be aware) edification:

On tapered NPT thread components, a thread sealant (pipe dope) to ensure a leak-free connection is mandatory.

On the other hand, AN (or equivalent) fittings (like those on this application) are flare-type compression fittings, therefore do not require any form of thread sealant.



IMO, of course.
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Last edited by Jozef Schumann; 05-18-2020 at 10:57 AM.. Reason: typo
Old 05-18-2020, 10:18 AM
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Why did you replace the line in the first place? I've never seen one fail. Also, anything aftermarket (with very few exceptions) is questionable on these machines. BMW employs some fine engineers who do the marque proud. It's the corporate bean counters looking toward investor profits who fetzer their efforts. In my experiences, more times than not - replacing an OE component with aftermarket is a step backwards.

Simple remedy is refit (if it's servicable) the take off, or purchase an original. They're about $200 + shipping new - but there's more than likely a pelican who has a used one with plenty of service life left willing to sell for not-so-much.
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Old 05-18-2020, 10:44 AM
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I replaced the line because: 1) I was in there anyway, 2) it was rusty, and 3) I'm working on moving the handlebars to a position that fits me better, so I need a longer line.

That spot you marked with your comment in the picture above is where I thought there might be a problem. The Spiegler banjo is thicker, so the lower crush washer ends up sitting around the threads, rather than at that little shoulder.

However, I think all the sealing is supposed to happen between the slave face, the crush washer, and the banjo face. Even if fluid can leak up through the threads (which it probably can) it shouldn't be able to get out through any of the surfaces touching a crush washer face. So I guess for some reason, one of those sealing surfaces (red circles) is not sealing. I just have to figure out why.
Old 05-18-2020, 12:51 PM
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Did they give you a torque value for that? Is the crush washer too big? It doesn't look like it, but I'm having a serious "WTF?" moment over this. It's not a brake line. There's hardly any pressure on it at all. Have you contacted Spiegler? Is that an OEM slave cylinder? I don't think it would matter, I'm just curious.

That being said, I'm getting on the "put the old stuff back on and forget about it" program.
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Old 05-18-2020, 04:29 PM
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Not a proper depth guage but suffices as a rough estimate. Note depth of threaded hole = approx 19.25mm



Length of Banjo bolt as compared to the caliper tang above shows ample distance to the bottom of slave fluid chamber.


Banjo bolt threaded into slave shows orifice orientation in relation to it's location to the banjo fitting. Obviously, the crush washers would disallow this degree of depth, rather; the orifice would closely coincide with the O.E. banjo fitting. Also, the raised register limits the range of installed depth.



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Old 05-18-2020, 04:40 PM
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Note the thread diameter.



Note the lower index register diameter.



Note the upper shoulder, index register diameter.



The differences are significant.

The importance of the lower register being properly located cannot be overemphasized. If it were unnecessary it would not be there as the manufacturing process would be one step less by simply threading the bolt to an end point. The raised register, as all of the details and dimensions of the bolt - are part of a system. Change one thing and you no longer have a viable system as designed. This is what you are now discovering.

"If it aint broke - don't fix it"
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Old 05-18-2020, 05:01 PM
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Quote:
Originally Posted by JimMoore View Post
Did they give you a torque value for that?
18Nm (13.25 ft-lb) at the master and 9Nm (a mere 6.64 ft-lb) at the slave as per factory workshop manual.

J.S.
Old 05-18-2020, 05:23 PM
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Hey spacey, as an aside...did you drill a vent in the bottom of the slave surround? A bunch of us did that as a preventative measure.

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Old 05-18-2020, 06:49 PM
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