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Discussion Starter #1 (Edited)
So in between then and now I had a toddler... kinda took me out of the motorcycling hobby for a few years and my 2001 Ducati Monster 748 has been waiting to ride again. I was halfway through rebuilding the clutch master cylinder at the time, and now things have gotten a bit disorganized- I'm trying to put it back together with the kit I bought. I basically have 3 problems preventing me from wrapping up that task:
1. I'm missing the leaflet that came with the rebuild kit- as I recall it was pretty ambiguous and needlessly complicated as well (in 6 languages to boot!).
2. I don't know where this plain round O-ring goes (if anywhere).
3. I had to destructively remove the old boot, teflon seal, and aluminum (press fit) ring, so once I reassemble this cylinder I want to be very sure all the parts are present and in the right order, or else it's not going to want to come apart easily.

The vibe I'm getting is that this kit fit an assortment of cylinder assemblies and so some of these parts are superfluous to my model. Probably explains #2 above, however I also don't understand why the piston has a seemingly unused groove in the middle. Hmm.
I seem to be missing the little pill shaped steel plunger with round ends. Of all the things to be missing that's the most fortunate as I have a metal shop handy and can turn any steel rod into that easily enough- I just need the dimensions, and if I'm even close it will probably work since the rest of the system is adjustable. (it looks like around .5cm x 2cm)

Anyway, if anyone can offer some advice I'd be very grateful. Particularly if you could explain the O-ring, and supply dimensions for that plunger rod I think I'd be all set to put this assembly back together. Thanks so much!

(here's a pic (not mine) of the kit I have/had):
https://www.gutsibits.co.uk/prod_img/lrg/IMG_0592.jpg
 

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Discussion Starter #4
It helps a bit in that it generally reinforces what I was thinking- but it's not the same model evidently. I don't see a plain o-ring in your exploded view, and I don't see a spot for it in mine either, so I think it's just a part for some other configuration. One thing I didn't mention is that I also lost the little brass washer that seems to go behind the rubber plunger cup. That's ok though, I can reuse the old one since it's not a wear component. Also, it looks like your plunger rod is integrated into your handle unlike mine so we can't address the dimensions very well. Anyway, thanks for the photo, I appreciate it!
 

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On the top is a 90 deg black connector for the hose to reservoir, maybe the o ring fits in there.
been a long time since I had one apart, so could be wrong, but it must seal somehow.
 

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So in between then and now I had a toddler... kinda took me out of the motorcycling hobby for a few years and my 2001 Ducati Monster 748 has been waiting to ride again. I was halfway through rebuilding the clutch master cylinder at the time, and now things have gotten a bit disorganized- I'm trying to put it back together with the kit I bought. I basically have 3 problems preventing me from wrapping up that task:
1. I'm missing the leaflet that came with the rebuild kit- as I recall it was pretty ambiguous and needlessly complicated as well (in 6 languages to boot!).
2. I don't know where this plain round O-ring goes (if anywhere).
3. I had to destructively remove the old boot, teflon seal, and aluminum (press fit) ring, so once I reassemble this cylinder I want to be very sure all the parts are present and in the right order, or else it's not going to want to come apart easily.

The vibe I'm getting is that this kit fit an assortment of cylinder assemblies and so some of these parts are superfluous to my model. Probably explains #2 above, however I also don't understand why the piston has a seemingly unused groove in the middle. Hmm.
I seem to be missing the little pill shaped steel plunger with round ends. Of all the things to be missing that's the most fortunate as I have a metal shop handy and can turn any steel rod into that easily enough- I just need the dimensions, and if I'm even close it will probably work since the rest of the system is adjustable. (it looks like around .5cm x 2cm)

Anyway, if anyone can offer some advice I'd be very grateful. Particularly if you could explain the O-ring, and supply dimensions for that plunger rod I think I'd be all set to put this assembly back together. Thanks so much!

(here's a pic (not mine) of the kit I have/had):
https://www.gutsibits.co.uk/prod_img/lrg/IMG_0592.jpg
Looks like roughly the same kit I need to track down eventually. Probably different diameter though.
225491

Starting with the piston, the small brass washer goes on the piston, then the actual seal, then the silver retainer. The spring is the first thing that goes in the bore, followed by the piston assembly.
IMG_20201016_221701955-01.jpeg


You can't see it well in the photo, but then the large o-ring, the white plastic piece that holds the o-ring in place as well as the outer dust seal. Then the large brass ring presses it all in tight.
 

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Discussion Starter #7
Ahhhhh! Yes, I see how that O-ring could fit in there behind the teflon bushing! Thanks! I'm so glad I checked here before press fiting the ring into the assembly- it would be a real bear to get that back out.
The only question I have left is about the dimensions of that steel plunger. I'm still missing that part so will have to fabricate it- not a critical thing since things are adjustable but if I'm going to the trouble I may as well match the factory spec. Also, it doesn't effect the rest of the assembly since I can install and remove without disassembling the rest, so I'll get started on the rest of it and sort out the details later. I never did figure out why that groove on the piston exists but I guess it doesn't matter!
thanks again!


Looks like roughly the same kit I need to track down eventually. Probably different diameter though.
View attachment 225491
Starting with the piston, the small brass washer goes on the piston, then the actual seal, then the silver retainer. The spring is the first thing that goes in the bore, followed by the piston assembly.
View attachment 225492

You can't see it well in the photo, but then the large o-ring, the white plastic piece that holds the o-ring in place as well as the outer dust seal. Then the large brass ring presses it all in tight.
 

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Ahhhhh! Yes, I see how that O-ring could fit in there behind the teflon bushing! Thanks! I'm so glad I checked here before press fiting the ring into the assembly- it would be a real bear to get that back out.
The only question I have left is about the dimensions of that steel plunger. I'm still missing that part so will have to fabricate it- not a critical thing since things are adjustable but if I'm going to the trouble I may as well match the factory spec. Also, it doesn't effect the rest of the assembly since I can install and remove without disassembling the rest, so I'll get started on the rest of it and sort out the details later. I never did figure out why that groove on the piston exists but I guess it doesn't matter!
thanks again!
5 X 26mm on the plunger rod.

The groove actually lines up with the second port in the reservoir. That area fills with brake fluid as well. The piston seal is designed so a small amount of fluid can slip past it when the lever is released. This allows it to retract more quickly until it reaches the fluid port and the pressure can equalize among all three areas.
 

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Discussion Starter #9
Super helpful! thanks! You saved the day!
5 X 26mm on the plunger rod.

The groove actually lines up with the second port in the reservoir. That area fills with brake fluid as well. The piston seal is designed so a small amount of fluid can slip past it when the lever is released. This allows it to retract more quickly until it reaches the fluid port and the pressure can equalize among all three areas.
 
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