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Just been searching for Ducati 250 parts and stumbled over this.
 

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And, hey, I'm thrilled to get any feedback on this. This site is so dead, I was debating whether or not to keep updating this thread at all.
No, you should not be updating this thread. You should not be doing anything related to this bike at all. you should be spending your time on the Aeromunchi-Ducati special!

(Yeah, I'm on Advrider too...)
 

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Discussion Starter · #545 ·
No, you should not be updating this thread. You should not be doing anything related to this bike at all. you should be spending your time on the Aeromunchi-Ducati special!

(Yeah, I'm on Advrider too...)
Funny you should bring that up. I am refurbishing ADS's brake components right now.

103896
 

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Discussion Starter · #547 ·
I'm still waiting on my caliper rebuild kit, so I looked for something else to accomplish this morning.
The handlebars, from a Honda VTR250 Interceptor, were originally designed to bolt both around the fork tube and down to the top triple clamp. That second attachment is not an option with the GS750 front end.

They clamp to the fork tubes using only one pinch bolt per side, and I have never liked that there isn't a way to positively locate them. Even with the bolt torqued down five grunts tight, they can still be made to rotate with a good shove on the end of the bar. So I made a bar out of aluminum stock that links the two sides together. I need to replace the pinch bolts with some extended bolts (6mm x 70mm) and an extra pair of nuts to tie it all together. It's not very elegant, but perhaps I can hide it or integrate it somehow whenever I mount gauges. Or it will just be more ugliness.
 

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Discussion Starter · #548 ·
The master cylinder is rebuilt. I haven't replaced the caliper piston and seal yet. Instead, I took advantage of a sunny, 80-degree day to paint the brake components with Eastwood Brake Gray. It's the only truly brake-fluid-resistant paint I've found. The finish is more metallic silver than gray, and does a believable imitation of raw cast metal. It looks very different than the typical Suzuki satin black, but I kind of like it.



 

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Discussion Starter · #549 · (Edited)
I got the front brake functional last night.

I assembled the rebuilt caliper using the pads that came with it, because they didn't have much wear. I hooked everything up, filled the master cylinder with DOT 4, and attempted to bleed the line. After 30 minutes or so, the fluid in the reservoir hadn't dropped, at which point I naturally assumed that I had done something wrong. I took everything off the bike and stripped the master cylinder down again — tearing the new dust boot in the process. GRRR! Worse yet, I hadn't even needed to disassemble it. Nothing was amiss inside and a simple bench test would have demonstrated that it was sucking and puffing well enough. Like I said, it's been a long time since I've done this.

Like so many other points along this journey, the path forward was to spend money on the proper tool. I ordered a $40 vacuum pump from Amazon yesterday, which amazingly was waiting for me when I got home from work.

With a bit of negative pressure from the pump at one end and some pumps on the brake handle at the other, I was in business! The used pads and disc will need to bed in, at which point I will probably bleed it again, but that's way down the road. For now, the brake lever feels firm, and the caliper releases properly when you let off, so I'm calling that a win.

I'm not sure how to address the ripped boot. It seems silly to order another whole rebuild parts set just for that little rubber part, especially when the system works fine now. In addition to my dust boot issue, I discovered some unpleasant aspects of the Eastwood brake paint. It might be brake-fluid-resistant, but it's not totally impervious to it. During all my efforts, I let brake fluid get on the the painted exterior of both the master cylinder and caliper. The paint hazed almost immediately. I was able to buff the caliper back to an acceptable finish where it shows, but when I did the same thing with the master cylinder, the black OE finish started showing through. So it will need to get a repaint at some point. However, cosmetics in general won't be much of a concern to me until such point as I have a running, rideable bike.

Another minor annoyance: When I went to attach the clip that keeps the brake line from chaffing against anything, I discovered a broken screw in the bottom triple clamp. Gettng a drill in there will require taking the front wheel off, so that's something else I'm deferring until later.
 

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Discussion Starter · #550 ·
I didn't think it would work, but good ol' cyanoacrylate (aka Super Glue, Krazy Glue) bonded the master cylinder dust boot I tore when I took it back apart. There's one little 2-3 mm section that's not quite airtight, but it's as good as it needs to be. I had to stretch it over the top of the piston to install it, so I am confident the bond is at least a strong as the rubber.

 

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Discussion Starter · #551 ·
A helpful comment on another forum got me thinking, and ultimately led me to create a much less ugly and obvious brace arrangement for the bars, which simultaneously adds some redundancy by using the original attachment locations. I split the bar between the two clip-ons into two shorter straps and cut a semicircle out of each to clear the fork tube. I then turned some cones out of aluminum to replace the rubber instrument cushions. (I actually still have one more to make. The lower one on the throttle side is missing.) A countersunk hole under the handlebar accepts a stainless flat-head Allen screw. This raises the bars up by the thickness of the alloy, but I'm perfectly okay with that.

Once I'm done, I will round the ends and buff them up to make them look pretty.

 

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The bladder is not just for dust, ever notice how there is often water on top of the rubber when you take the cap off the vented brake master cylinder, the boot is to prevent water from condensation mixing with the brake fluid. ;)
 

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Discussion Starter · #553 ·
The bladder is not just for dust, ever notice how there is often water on top of the rubber when you take the cap off the vented brake master cylinder, the boot is to prevent water from condensation mixing with the brake fluid. ;)
You mean water vapor can get in past the piston seal?
 

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Discussion Starter · #554 ·
I made new locating cones of the proper height for the handlebar stays, and rounded the ends of the bars. Just trying to do a little every day. The bolts will get nylock nuts for final assembly.


 

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Discussion Starter · #555 ·
Keeping with my mantra, "Do a little something every chance you get," I mounted the lower chain guard this morning. I bought one from a '75 DT175, so it should just bolt up to my DT swingarm, right? Of course not—this is Bultakenstein, after all. Because my chain runs closer to the centerline, I needed to shift the guard over 11mm with a couple of custom spacers.




I would love to tidy this up, such as trimming the rear spacer block to match the contour of the swingarm and getting matching hardware (combining hex head and socket head bolts is so gauche!), but I've already devoted about 90 minutes to this one simple task, and when I look at this bike, I see a thousand little tasks like that. Stuff like that can wait for the obligatory teardown after it can move under its own power. So for now, it's on to other bigger concerns.

I have two more items on the to-do list prior to building the engine: fabricating an upper chain guard (I promised myself I wouldn't knowingly build a death-trap), and welding (or possibly MIG brazing) the rear swingarm spacers. (The left one can be seen hanging limply behind the chain adjuster at the upper right of the last photo.)
 

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You mean water vapor can get in past the piston seal?
I mean the area in the master cylinder reservoir that contains air is vented, it has two be, it needs to remain at atmospheric pressure to work. That air volume (above the bladder) can and frequently does contain atmospheric moisture, the bladder helps to stop that water from mixing with the brake fluid.
... we might be talking about a different chunk of rubber. I'm talking about the one inside the brake master cylinder reservoir.
 

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Discussion Starter · #559 ·
I mean the area in the master cylinder reservoir that contains air is vented, it has two be, it needs to remain at atmospheric pressure to work. That air volume (above the bladder) can and frequently does contain atmospheric moisture, the bladder helps to stop that water from mixing with the brake fluid.
... we might be talking about a different chunk of rubber. I'm talking about the one inside the brake master cylinder reservoir.
The rubber part I repaired is the external boot over the actuator piston where it contacts the brake lever. My diaphragm is fine.
 
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