Air in clutch master cylinder?! 696

[malamikigo]

My stock clutch slave cylinder on my 696 lost its load all over my floor slowly over the winter months.  As such, I replaced it with an Oberon unit a couple weeks ago.  I am a NOOB to maintenance, so I got a friend who has a 1098 to come over and help me with the bleeding.  

But we are stuck.  

- When I installed the slave cylinder I did fill it full of brake fluid before attaching the hose.  

- He used a mityvac to bleed via the bleed screw on the slave cylinder, and then when that didn't seem to do the trick he also used a syringe and reverse-flushed the line.  There did not appear to be any air bubbles popping up into the reservoir as he pushed fluid back up into it, and he said he was pretty certain the line and slave cylinder were bled properly.

At this point, the rear wheel STILL spun quickly in 1st gear with the clutch lever fully pulled in.  He said that on his bike, he would typically bleed the master cylinder at that point, which would do the trick.  But the 696 has no bleed screw on the master cylinder?!?  How the heck are you supposed to bleed it?  


So yea. Stuck, bigtime.  He says he's 90% sure there's air in the master cylinder but wasn't sure how to go about bleeding it without a bleed screw.

Help!  Really want to get this figured out!

[Slide Panda]

Remember a wet clutch with cold oil will spin the wheel if its on a stand. If the bike was on the ground, would it pull - transmit enough power to the wheel to move the bike?

One simple thing you can do, is strap the lever to the bar for a while. At least overnight, but 24 hours would be great. Doing so opens the passage from the line and master to the reservoir allowing any annoying bubbles stuck up high to work out of the fluid column

[malamikigo]

Yea, the lever is strapped to the bar right now, gonna leave it there till monday cause i don't have time to work on it tomorrow anyway. 

The rear wheel was spinning pretty darn fast.  I put my foot against and it didn't stop.  I think it would be pushing the bike forward if it was on the ground.  The oil was definitely cold, though.  But I think it's more than cold oil issue, the wheel was just spinning too fast, in my uneducated opinion. 

[Howie]

When bleeding it is also good to try and keep the master as close to horizontal as possible, though reverse bleeding should help with that.  You can bleed the master by cracking the banjo bolt.  I don't like doing that since it can be messy.  Do keep in mind if your Oberon's piston is a larger diameter than stock travel is reduced, which can increase clutch drag.

[malamikigo]

I understand a bit of increased clutch drag with the Oberon, but it still seems a bit excessive to me.  I dunno.  Like i said, I'm a noob and don't know anything about this stuff, but...I feel like there must still be a little air in the system. The master was very horizontal.  Bike was on rear stand with the handlebars square, so it was about as level as it can be. 

Could you describe the process of bleeding the master by cracking the banjo?  I'm fine with a little messy, I've got plenty of shop towels to keep things under control...I just want to make sure it's bled as well as possible.

[Howie]

With the lever squeezed, just like when using a bleeder screw, slightly loosen the banjo bolt, allowing fluid and air to escape.  Tighten.  Release lever.  Was, rinse, repeat until all air is gone.  Messy was an understatement.  Brake fluid damages paint and some plastic.  I would try everything else first.  Another way to reverse bleed is remove the slave and manually push the piston back into the cylinder.  You will be displacing a lot of fluid and a column of fluid will squirt from the reservoir so again, *caution*. 

Not foolproof, but a way to check for air is to squeeze the lever, then release the lever slowly.  You should see a steady stream of brake fluid with no air bubbles.  And again, *caution*.  In theory, bleeding is easy.  In practice, not so easy, particularly with motorcycles.  Hopefully the lever tied to the bar trick will have worked for you.  If not, try conventional bleeding first. 

[malamikigo]

Another way to reverse bleed is remove the slave and manually push the piston back into the cylinder.  You will be displacing a lot of fluid and a column of fluid will squirt from the reservoir so again, *caution*. 

Not foolproof, but a way to check for air is to squeeze the lever, then release the lever slowly.  You should see a steady stream of brake fluid with no air bubbles.  And again, *caution*.  In theory, bleeding is easy.  In practice, not so easy, particularly with motorcycles.

^Everything in this part of the reply we did try.  When the piston was pushed back into the cylinder, there was a little volcano of fluid in the reservoir and it appeared to be free of any air bubbles.

Same with slowly releasing the lever.  Stream of fluid popping up into the reservoir, appeared to be no air.

With the lever squeezed, just like when using a bleeder screw, slightly loosen the banjo bolt, allowing fluid and air to escape.  Tighten.  Release lever.  Was, rinse, repeat until all air is gone.  Messy was an understatement.  Brake fluid damages paint and some plastic.  I would try everything else first. 

Definitely sounds messy.  I'll see how the lever tied to the bar works out first before considering this. 

[Privateer]

with the bike on a stand, the rear wheel will turn in neutral or in-gear-lever-pulled.

At least on my bike it does.  I wondered about it too and was told here it was perfectly normal.

[Howie]

with the bike on a stand, the rear wheel will turn in neutral or in-gear-lever-pulled.

At least on my bike it does.  I wondered about it too and was told here it was perfectly normal.

^Everything in this part of the reply we did try.  When the piston was pushed back into the cylinder, there was a little volcano of fluid in the reservoir and it appeared to be free of any air bubbles.

Same with slowly releasing the lever.  Stream of fluid popping up into the reservoir, appeared to be no air.

Definitely sounds messy.  I'll see how the lever tied to the bar works out first before considering this. 

It is, the question is how much is normal.

My next step would be get it off the stand and, while sitting on the bike, start it in neutral.  With the brake fully applied, clutch squeezed to the grip, shift into first.  If the bike stalls you have a bad case of drag.  If the bike doesn't stall or try to move away as you carefully start to release the brake you are in pretty good shape.  Can you easily find neutral you are good to go.  Can't find neutral easy?  Go around the block a couple of times to get the oil warm and see if finding neutral is easier. 

Do you have adjustable levers? 

[stopintime]

The coffin master cylinder and wet clutch needs to be fine tuned at the lever, even more so if you go from stock 26 to aftermarket 29 mm. If the various bleeding tricks doesn't solve your issue, try the fine adjustment described here: http://www.ducatisuite.com/leverchange.html

[malamikigo]

Thanks for the suggestions, I'll be working on it again tomorrow to see if its any better.  Will report back!

[Raux]

took me forever to get my clutch system bled.

[malamikigo]

...well that's not uplifting to hear!      How long is "forever"?  And what were the quirks you had to work out? 

[Raux]

3 days and almost a full bottle of fluid.

[malamikigo]

Update:

After leaving the lever strapped to the bar for about 36 hours, the tire still spun pretty quick in 1st gear on the rear stand with the lever pulled in. 

However,

When I put the bike down on the ground, clunked it into 1st with the lever pulled in, nothing unfortunate happened.  Felt totally normal, actually.  The bike didn't lurch forward, stall, or do anything that felt out of the ordinary to me. 

So I grabbed my helmet and took it for a couple spins around the block.  It shifted smooth and easily, had no troubles finding neutral at a stop, and everything felt just as I would've thought it should. 

So......seems like everything's fine??