Clutch line air

[LBump]

So, I was riding along AZ. 260 after putting in some 1800 miles and noticed the clutch went way spongy. The bike was towed down to the great folks at GO AZ BMW and they came back saying there was air in the line. The slave and master were tested and OK. Were did the 'air' come from... any thoughts?? Bike is a 09 RT with 7500 miles. Thanks for any imput!

[dirtrider]

Afternoon kodabromide

 

That is somewhat common on the 1200GS. In fact there is a service bulletin to cut the clutch line zip tie and let the line float upwards to remove the air trapping loop.

 

I looked at my 1200RT clutch line routing & it is pretty close to the GS routing so I clipped the tie strap on that and re-routed it so it didn’t have that low loop in it.

 

I haven’t ever seen a service bulletin on the 1200 RT and your bike is the fist RT I have heard of with the air problem. Obviously my RT has the re-routed line so that is no help other than my bike hasn’t had the air pocket problem.

 

The problem seems to happen on the GS only when many miles of hi-way with no down shifting or clutch usage. I seldom go more than 100 miles without downshifting or doing something with the clutch.

 

Otherwise, possibly a seal problem on the slave cylinder that lets air in but no fluid out. I believe somewhere along the 1200RT line there was an improved slave cylinder put in production (so maybe).

 

 

 

[NewBlue]

Heard about this on a few RT's and it ended up being the slave cylinder. I believe there is a new version cylinder that will correct this condition.

 

The loss of lever resistance was noted after riding on slab for a few hours then noted when exiting, loss of lever and had to be pumped. New fluid and bleed did not correct until the slave was replaced.

 

I still wonder how air could get in but no fluid out, I'll just have to trust what was posted.

[dirtrider]

----I still wonder how air could get in but no fluid out, I'll just have to trust what was posted.

 

According to the service bulletin from BMW.

 

 

 

“Cause: Vibration/Cavitation can create clutch fluid air bubbles.”

 

I would presume the new slave cylinder for the RT is either tighter so the piston can’t vibrate or is sealed better so the piston vibration can’t work air in at the seal area. I think the new slave cyl P/N is – 21527724542 but not sure when it was phased into production. On the GS/GSA-apparently the line re-routing allows the air to work up the line and not become a big air bubble in the line.

 

 

[NewBlue]

----I still wonder how air could get in but no fluid out, I'll just have to trust what was posted.

 

According to the service bulletin from BMW.

 

 

 

“Cause: Vibration/Cavitation can create clutch fluid air bubbles.”

 

I would presume the new slave cylinder for the RT is either tighter so the piston can’t vibrate or is sealed better so the piston vibration can’t work air in at the seal area. I think the new slave cyl P/N is – 21527724542 but not sure when it was phased into production. On the GS/GSA-apparently the line re-routing allows the air to work up the line and not become a big air bubble in the line.

 

 

Cavitation, OK, that makes sense. Lower pressure in the slave cylinder, increased fluid temp from extended riding.

Outside air entering, that one I'll still struggle with.

[KDeline]

Oh come on! They are pulling these reasons out of their butt. I had a brand new one fail in less then 2000 miles after replacing a leaking one on our Alaska trip last year. What fun that was failing twice in one trip added to all the other problems we had.

[LBump]

Thanks for the insights. I'll have one of the local dealers look into the slave cylinder part number difference. Perhaps there's a different 'sealing' method... Perhaps there was air left in there from the factory... Beavis might have answered his phone on the prduction line you never know... I'll be checking it out as the miles go on.

[NewBlue]

Oh come on! They are pulling these reasons out of their butt. I had a brand new one fail in less then 2000 miles after replacing a leaking one on our Alaska trip last year. What fun that was failing twice in one trip added to all the other problems we had.

 

WHAT.... you don't believe that the slave is vibrating at a frequency that turns it into an ultrasonic mineral oil humidifier.

 

Now that I read what I wrote, not so sure I buy it either.

 

Maybe Ivan assembled it <----- that's a Ural reference.

[dirtrider]

Morning kodabromide

 

I doubt any air was left in the system as built or the clutch wouldn’t have worked when you rode it home.

 

I sure can’t tell you where the air is coming in from but it basically has two places to enter. From the slave cylinder and that would be from the piston seal area, or from the master cylinder area with the air getting into the somewhat thick fluid from vibration and foaming then that aerated emulsion pumping down the line during slave cyl piston vibration movement. (it wouldn’t have to make it all the way down only past the low spot in the line)

 

Something odd going on there as I had a friend with a GSA have the same issue last spring on his way to Alaska. He was a miles from nowhere when his clutch lever went limp and he couldn’t de-clutch at stops or to shift. He called me to ask what I thought went wrong (he thought he had a failed clutch). I told him probably either a failed slave cylinder or air in the system. Then told him of the BMW campaign to cut the tie straps & re-route the clutch line to remove the air trapping loop. Also told him he might want to get the front of the bike as high as possible after re-routing the line to maybe get some of the air to purge up & out.

 

He cut the line loose and had a passing truck driver help him push the front of the bike up the side of the ditch nose high. He called later that day to tell me with a bit of lever pumping and he got enough clutch back to ride it with the intent of getting to a place to have it repaired. He said as he rode on the clutch returned to normal and hasn’t given him any problems since (he has about 90K on the bike now).

 

Obviously BMW seems to recognize a problem in that area (at least on the GS/GSA) as they have an ongoing “campaign” to re-route the clutch line (not a re-call though) . I’m not sure on the RT but some place along the line they released a different part number slave cylinder.

 

Here’s my take--- You would think that a simple slave cylinder or slave cylinder (seal) failing would lead to air in the system ALL THE TIME, even riding locally or on short trips. The only failures like yours (limp clutch) that I have heard of are mostly GS/GSA’s and couple of RT’s & AFAIK those have ALL come after a long high speed hiway run with NO clutch usage for hours. SO, that leads me to believe there is something to the vibration end of it.

 

 

 

 

[CoarsegoldKid]

I live close to high elevation passes of the Sierra. Several times a year I ride them. About a two years ago I was riding through Yosemite on Tioga Pass which is about 8-9K feet in altitude. The air temp was on the hot side. Very little shifting necessary on this day. Then I noticed my clutch exhibited increased free play when pulling into a viewpoint, almost about half the throw of the lever was free. As I got lower in altitude the clutch came back to normal. I never did anything about it and the symptom has never recurred. I will check the routing of the clutch line next time I take the tupperware off to see if there is a spot where air can collect. I would be interested in hearing more on this updated slave.

[Firefight911]

I live close to high elevation passes of the Sierra. Several times a year I ride them. About a two years ago I was riding through Yosemite on Tioga Pass which is about 8-9K feet in altitude. The air temp was on the hot side. Very little shifting necessary on this day. Then I noticed my clutch exhibited increased free play when pulling into a viewpoint, almost about half the throw of the lever was free.

 

Though on a different bike, this is the exact symptoms that happened to cause my GT to be bought back. They could never fix it and it would never resolve. It was always there.