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R1150GS clutch slave modification

The Fabricator

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The Fabricator

I have always had a hard time taking off with my 2000 R1150GS due to the tall first gear and the narrow friction zone of the dry clutch.  And the lever pull effort is excessive.

I also own a 1977 R100/7.  I had rigged up a pulley system for the clutch that reduces the lever effort by 1/2 and doubles the friction zone. [I have seen that modification offered as a kit.]

For my 1150, there were 3 options.

1.  Fabricate a clutch lever that has a relocated pivot point for increased leverage.  I never measured things to determine the effort reduction, but I suspected it would not be enough reduction.

2. Find/install a master cylinder with a smaller piston.  Then I would have to deal with the switches and wiring.  That was not attractive.

3. Find/install a slave cylinder with a larger piston.  I searched the internet and found nothing offered nor a modification.


I am a retired MC mechanic.  I had saved [for a few decades]a Yamaha clutch slave cylinder from the junk pile.


The stock slave cylinder piston is 24mm.  My 'saved' cylinder was 38mm.  That calculates to a 2.5x reduction of effort.

At this time I had the transmission out of the bike, so it was a good time to perform this mod as access to the slave area with the transmission mounted is very limited.


A trolly I fabricated.  This makes transmission removal/installation easy.




The BMW slave cylinder                                                                    Yamaha slave cylinder.  Note that it does not

                                                                                                                   fit into the slave cavity in the transmission.     


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BMW uses a bearing in the slave piston where the            Yamaha uses a ball which makes a single point

clutch push rod presses on the piston.                                   point of contact with the push rod.  I chose to 

                                                                                                                  retain the BMW system.  I removed the piston

                                                                                                                   from the cylinder.

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I fabricated a carrier for the BMW slave piston.                   The carrier inserted into the cylinder cavity.  It projects

The carrier is a precise fit into the slave cavity in                  out of the cavity this amount in operation.

the transmission.  The carrier can slide in the cavity.


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This is the set up with the BMW piston, carrier, Yamaha 

piston and cylinder.  The ring is an adapter to accommodate 

the different cylinder diameters, bolt patterns and distances.                               The adapter and piston carrier in place on the 

The 3 counter sunk holes fasten the adapter to the transmission                            transmission.

and the 2 other holes fasten the cylinder to the ring.

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The Yamaha cylinder mounted on the adapter plate.                                I fabricated a longer bolt.  Stock bolt on right.

Note 2 hoses; one from the master and one for bleeding                         I had to jump through some hoops to figure out how to

air from the system.   The stock bleeder valve is not used.                       use  hoses with 6mm bolt ports with 10mm bolt ports on

                                                                                                                                           the slave.

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I drilled a 10mm bolt for a 6mm hole, threaded it, cut that off

so it was a sleeve, thread that into the port with

epoxy on the threads.




So, what's the verdict?


It didn't work.


Seems when the force at the clutch lever is reduced by 2.5x, the slave piston travel is ALSO reduced 2.5x.  I could get the clutch to release if I pumped the lever 3x.  

In my defense [one of those 'Why didn't I figure that out ahead of time!], there was no way of knowing how much travel is enough.  I was going by my old R100/7 mod, which was a 2x reduction, so I figured 2.5x was close.  And, I had a cylinder at hand.


After a little bit of fuming, I calculated a 32mm piston would yield a 1.77x reduction, looked on the internet for a 32mm cylinder, found a K1200 was 32mm, ordered $50 unit including shipping off ebay, and 2 days later had it mounted.  It required an additional adapter ring and the same monkey shines for the hose port threads.  But it's done.


The verdict?


It works PERFECTLY.  The lever effort is a 2 finger affair.  The friction zone is about 1/2 the clutch lever sweep.  I can pull away with minimal rev's and an easy smooth release of the clutch lever.  The clutch does not drag, as evidenced by no difference in shifting or finding neutral [if you don't know, a dragging clutch makes neutral selection difficult.].


My bike.  Clutch slave is not the only modification.






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