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Discussion Starter #1
I came across an unfortunate common problem associated with the 999 Clutch Master Cylinder. I was losing Clutch pressure over a short period of time and experiencing Clutch creep. If I pulled up to a set of traffic lights and had the Clutch pulled in the Bike would begin to creep as the Clutch slowly started to engage.
I am familiar with the technique used to properly bleed the Clutch and did this many times. I swapped out the Slave Cylinder to make sure that was not the problem (it wasn't). I replaced all the copper crush washers to make sure no air was getting in through a faulty washer and inspected the Clutch line very closely. No joy.
I bought a very good condition 1198 Clutch Master Cylinder which was dead easy to bolt on and after a quick bleed was up and working a treat. Having said that every time I looked down at the unmatched pumps I wanted to replace my Clutch Master to match my Brake Master (its a ducati thing).
The 999 Master Cylinder is a non rebuildable unit. However I priced a replacement unit and at $525.00 I decided that I would pull it apart and see what I could do.
Firstly remove the Clutch Master Cylinder with the Lever attached. Remove the little Clutch electrical switch by gently levering it off with a small flathead screwdriver. It just clips in, nothing will break off. Remove the Lever by unclipping the C-clip, pull out the centre pin and you now have the Lever off the Master Cylinder. There is a dust cover that you now need to remove. It is in pretty firmly. Once again I used a small flathead screwdriver to lever the dust cover off. You will probably damage this in the process but don't worry, you will be replacing it anyway. Now you will see the plunger. Push it in and out a couple of times and it should push out of the barrel under the pressure of the spring behind it. Now you can pull it all the way out. Inspect the plunger and you will see that on one end there is a bell shaped seal that is held on by a C-clip. Remove the C-clip and pull the seal off. Behind the seal there will be a thin stainless steel washer. Don't lose it. I took the Bell shaped rubber seal along with the plunger to a local Ducati parts supplier. We checked out a couple of BREMBO rebuild Kits. After we opened a couple of Kits to check out the rubber seals for size I settled on a BREMBO part # 110436291 15mm rebuild kit. You will use only 2 pieces of the Kit. The Bell shaped seal and the dust seal, and of course the little sachet of rubber grease to ease the seals back into place. Now the outside diameter of the bell shaped seal is exactly the same as the original but the internal diameter is slightly smaller. This did not pose a problem. I just eased it over the spline and all is good. The seal kit cost $29.00 Australian. Not a huge outlay when compared to the $525.00 Aust for a replacement Clutch Master Cylinder.
While you have the Master Cylinder off you should replace the 2 "O" rings that seal the plastic reservoir to the Master Cylinder. Remove the 6mm screw pin that you use to bleed the upper part of the system. Unscrew it all the way out. Now get a 6mm Allen socket, place the Cylinder in a vice, you will notice that there are to flat surfaces on the aluminium cylinder that allow you to get a decent grip without scratching the surface and unscrew the Allen keyed bolt. The reservoir will come off. There are 2 "O"rings on the bolt. use a pick to prise them off. Head down to your local Auto parts shop or a Bearing shop and buy 2 new ones. Cost me $2.00 Remember to use some rubber grease from your rebuild kit to ease the reassembly process.
Before I reassembled the Master Cylinder I inspected the old seal closely and noticed a wear mark in the rubber outer surface. I then looked into the Cylinder bore and noticed that the small hole that allows the Clutch Fluid in and out of the Cylinder when the Clutch is actuated was a similar size to the wear mark on the seal. I used a thin pin end scribe and felt a small lip on the side of the inlet/oulet hole. Enough to have caused the seal to fail over time. I then used a cotton tip wrapped with a small piece of 1200 grade wet and dry paper. Dipped it in Clutch fluid and carefully removed the bur on the inlet with some very small careful rotations just over the inlet. Then flushed out the bore with fluid to make sure any residual came out, it did.
It was a simple matter of reassembling the Master Cylinder, adding new fluid and bleeding the system. The result is a working Clutch Master Cylinder. I have taken the Bike out on a good few test runs in traffic, held the Clutch in for minutes on end and no Clutch creep at all. The Clutch take up is smooth and predictable. I purposely left off the Dust seal to keep an eye on leaks. No leaks so slipping the Dust seal back on will be a 10 minute job. The Original Dust seal has a stiff feel to its lip whereas the replacement seal is more flexible. It fits in fine and will do exactly the same job. I am including some photos that will hopefully describe the above. This may not be the fix for you but it seems to have worked for me. Cheers for now.
 

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Old Wizard
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There are 2 "O"rings on the bolt. use a pick to prise them off. Head down to your local Auto parts shop or a Bearing shop and buy 2 new ones. Cost me $2.00
Nice write-up, thanks.

You may, or may not be aware that brake fluid is not compatible with some o-ring materials. Viton should be used.

Marco Rubber | Fluid Compatibility Guide
 

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Discussion Starter #3
Thanks Shazaam. I purchased the O-rings from a Seal and Bearing place and asked if they were resistant to brake fluid and got the Ok. There was a cheaper material for O-rings that the sales guy did not recommend because of the brake fluid.
 

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I'll second the last question that was posed to the OP--should that second bell-shaped seal be replaced as well? Also, has anyone else tried this rebuild approach with positive results? I'm in the market for a master cylinder repair or replacement...
 

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The seal on the lever end is only to stop drainage from the master through the compensation port when the clutch lever is pulled. Since it is at atmospheric pressure, it's more like a wiper than a seal. Unless it is damaged, it will not leak. Silicone grease.
 

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Hi rigger
do you remember when you replaced the inner seal ring - was the new one without an axial groove?
My filing is that there is a groove on purpose in order to let the fluid go from behind the seal to front of the seal during release lift.
My problem is leaking outer seal - I will exchange it - but I am not sure if the inner is OK.
 

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The rubber bot on my 05 999s failed too soon (bike has only 2k miles) clutch leaked air. I ended up removing the whole clutch lever and master and reservoir of my 2004 Honda St1300abs and put it on the Duc. Everything worked fine. I taped the clutch safety switch and closed circle it.

Fyi I removed the stock clip ons and flipped them upside down so the angle of the clip ons is pointed up not down to help with a better seating position and also so the Honda reservoir don't hit the spedo cluster. It would be nice if I had a longer clutch fluid cable but the stock Duc one worked fine.
 
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