Clutch release failure

On my most recent trip, the master cylinder on my clutch began failing. I could pump the handle and get it to release but it would slowly release and engage as I held it. The BMW dealer in Sturgis first bled the clutch system and when that didn't help they installed a new kit in the master cylinder and bled the system, but that also didn't help. A close inspection shows no leaks in the line nor in the slave cylinder so the suspect is that it is somehow bypassing in the master cylinder. Have any other R1150RT owners experienced this issue (and more importantly, solved it)?

Good to see you on!
Might need the year for your R1150rt.
OM

The machine is an '02 R1150RT About 65K miles. The system has been flushed but appeared dirty when bled at Sturgis (after only a couple thousand miles from the fluid flush.)

jweyand said:

The machine is an '02 R1150RT About 65K miles. The system has been flushed but appeared dirty when bled at Sturgis (after only a couple thousand miles from the fluid flush.)

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Great, may take a day or so but I'll bet the Oilhead guys can suggest a cure.
OM

How exactly did they inspect the slave cylinder? You generally can't detect a leak until you remove the slave. A leak is into a semi-sealed recess in the tranny case and fluid is not noticeable until the cavity fills up and the fluid escapes forward through the input shaft, fouling the clutch.

PGlaves said:

How exactly did they inspect the slave cylinder? You generally can't detect a leak until you remove the slave. A leak is into a semi-sealed recess in the tranny case and fluid is noticeable until the cavity fills up and the fluid escapes forward through the input shaft, fouling the clutch.

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+1 With the master cylinder replaced, and assuming no obvious leaks from the clutch line, the slave is the only remaining part to leak, and you wouldn't see a leak from an external inspection. This is also *by far* the most common failure mode.

Any signs of leakage/wetting at the bottom of the mating surface between the engine and the tranny?

The only place for fluid to go from the slave's front end is along the throwout rod to the front of the tranny, and thence onto the clutch plate and into the space between the engine and tranny. (In theory, fluid could leak past a compromised rear input shaft seal and rear bearing into the tranny, but that is not common -- it is easier for the fluid to go forward to the clutch.)

I don't believe the people at Sturgis BMW do that much BMW work. I stopped there to get spark plugs for my dual spark 04 RT on the way to the rally. I told the parts guy that it was a dual spark 04 RT and he told me it only had two plugs. When I insisted that it had four he gave me four of the same plug. I informed him that there were two different kind. Luckily someone else behind the parts counter knew what I wanted.

It sounds like it's time to remove the Clutch Slave Cylinder and inspect it, as it's a known failure point.

Although the BMW manual says that the bike frame has to be moved in order to remove the slave cylinder, it can be done by removing only the rear wheel and rear shock, although it may help to loosen or remove the exhaust. The trick is to remove the three bolts that hold it to the transmission; remove the cable ties which hold the bleed line to the frame on the right side; and then find the angle and rotation of the slave that allows it to be "fiddled" out from the transmission. That should allow you to inspect it.

To get it past the structural tube that's behind it you may need to release or remove the banjo bolts that connect both cables. Remember that it's brake fluid which will eat your paint. So either protect everything or drain the clutch circuit before loosening the banjo bolts.

Once you get down there and find the cavity full of rotten brake fluid crud, take a good whiff and see if the fluid smells only like brake fluid or if there is a nice odor of gear lube with it. I'm 2 for 2 on pulling slave cylinders to find that the brake fluid leak attacked the rear gearbox seal (for the input shaft) and that it needed to be replaced as well. The rubber of the seal had bonded to the aluminum housing in both cases (thanks to the brake fluid) and I lost time fighting to get the seal out. The final technique involved a spring steel hook going through the screw holes which had ripped out, vice grips, wood blocks and a pry bar. I probably should have tried soaking the seal with fresh brake fluid before drilling / inserting the screws - might have helped. Clean the bore above the seal carefully before removing the seal if you have to.

Assuming you find a leak, pull the starter to see if the clutch is contaminated. I'm 1 for 2 on having the brake fluid & gear oil combo soak the clutch. Of course, the slave cylinder piston was getting stuck mid stroke on the other bike and its clutch slipped worse so both bikes got new clutches. I also added weep holes to the slave cylinder bore on both bikes and strongly suggested to their owners that they flush the brake and clutch fluid regularly.

If you decide to rebuild the slave cylinder rather than replace it, inspect the piston and bore to make sure they aren't damaged. Also check and re-grease the throw-out bearing.

This is what you're looking for:


This is what you want to see:


Also, here is a rebuilding kit available for $34.95 from Beemer Boneyard if the need arises
http://www.beemerboneyard.com/21522335061rk.html

We used to be able to buy new OEM Magura slave cylinders at a discounted dealer price from Mike, but due to a recent lawsuit by BMW against Magura, nobody can get Magura clutch slaves except the dealers. You can call Mike to see if he has any leftovers on the shelf, but once current stock is gone, he'll no longer be able to get BMW specific Magura products. BTW, pistons & bearings are not available anywhere. A good used one on Fleabay might do the trick too.

Paul, I was told by the service fellow that if the slave cyl was leaking you could see the fluid at the bottom of the motor. Today, I removed the side panels and when I got to the area behind the starter I could see evidence of fluid accumulated on the surface of the trans assy. I will begin an in depth tear-down tomorrow. I certainly appreciate the input from other riders. We know that experience is the best teacher, but not always the least expensive--unless it's someone else's.

jweyand said:

Paul, I was told by the service fellow that if the slave cyl was leaking you could see the fluid at the bottom of the motor.

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Only if the gasket is leaking, or somebody has drilled a drain hole, or fluid has already migrated forward and is apparent at the bellhousing weep hole after fouling the clutch. By then the bill is a couple thousand $$$ and it is too late for the easy repair.

Well, I found "what I wanted to see" when I got the slave cylinder out. It was wet with fluid but only slightly soiled in color. I expect to receive the rebuild kit from beemerboneyard by Wednesday. The various comments were most accurate--unlike the counsel I got in Sturgis at the BMW dealer. As always, the MOA members have been quite helpful with advice and tips. Thanks to all who took time to add wisdom!!

jweyand said:

Well, I found "what I wanted to see" when I got the slave cylinder out. It was wet with fluid but only slightly soiled in color. I expect to receive the rebuild kit from beemerboneyard by Wednesday. The various comments were most accurate--unlike the counsel I got in Sturgis at the BMW dealer. As always, the MOA members have been quite helpful with advice and tips. Thanks to all who took time to add wisdom!!

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Glad you identified the problem.

rocketmanli said:

This is what you're looking for:
View attachment 51317

This is what you want to see:
View attachment 51318

Also, here is a rebuilding kit available for $34.95 from Beemer Boneyard if the need arises
http://www.beemerboneyard.com/21522335061rk.html

We used to be able to buy new OEM Magura slave cylinders at a discounted dealer price from Mike, but due to a recent lawsuit by BMW against Magura, nobody can get Magura clutch slaves except the dealers. You can call Mike to see if he has any leftovers on the shelf, but once current stock is gone, he'll no longer be able to get BMW specific Magura products. BTW, pistons & bearings are not available anywhere. A good used one on Fleabay might do the trick too.

Click to expand...

Sadly I have not been able to put this kit to use yet.

By the time the slave fails, the piston has spun, (caused by the bearing running out of grease) damaging the anodize on the inner bore which then will not allow proper sealing. I have not had one with a perfect bore yet and have a box of hooped slaves here.

Also;
The little bearing is made by INA is only for sale to Magura for BMW - I tried to source the thru my company and came to a dead end.
It was specifically designed by BMW for this application.

My suggestion is to keep that little bearing lubed every 40,000 miles as a PM and properly lube the new one out of the box as they have minimum lube in the first place. My own is now at 183,000
Flush your fluid every 2 years as well.
Drill a hole at the bottom of the transmission chamber as well.

One of the many annoying things about owning a BMW (3 in my case) is the proprietary parts or sub-assemblies. A while ago I broke one of the H7 headlight bulb retaining springs in my new-to-me '09 R1200RT. The cost of a new one was $700! No springs were available anywhere in the planet, and the dealers said I had to buy a whole new headlight assembly for one broken clip. Nobody up and down the BMW chain would tell me where they got their clips, even though you know somebody, somewhere builds and installs these clips for BMW. End result was sending one of the good clips to a wire drawing company here on the East Coast who built me about 50, for a whopping $10.00 or so each. I kept a few for myself, sold a few at my cost, and sold the rest to Mike at Beemer Boneyard for him to re-sell. Amazing how you have to jump through hoops to get some parts sometimes.