Front disk brake lever movement.

toglhot

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I've just bled the front brakes, but not happy with the amount of lever movement.
It is a mongel system:
new pads,
new rubber hoses,
new stainless pistons,
aftermarket MC with adjustable lever,
17mm MC bore,
DOT 3 fluid,
copper washers throughout,
banjo fittings throughout,
lower caliper banjo fitting has a 10mm ally spacer with copper washers,
lower banjo bolt is a dual to give the height I need to give I needed to use a banjo on the caliper,
dual banjo bolt for height,
homemade hose junction so I could use the stock XS two hose system without the steel lines top and bottom, and
absolutely no leaks in the system.
The caliper is non floating so the calipers obviously have to be centred for best actuation. Mounted using stock mounting bolts, however, there is about 0.14mm offset to the outer.
To bleed, I loosened the caliper mount bolts so the calipers floated central.
When the lever is pumped dozens of times the lever remains the same, so I'm happy there is no air in the system.
Left overnight, lever movement remains the same, no leaks.
MC bore is 17mm so slightly larger than stock witch is 5/8"/15.8mm, but I don't imagine 1.2 mm larger MC bore is going to make that much difference.
The lever is one of those adjustable ones, so, when set closest to the bars, the leve travels all the way to the bars, when set fartherest away from the bars, the lever is about 20mm from the bars, but if really squeezed, even my arthritic hands can squeeze the lever all the the way so it actually touched.
I'm not that familiar with XS650s, this is the first one I've owned, but even my Triumph T140's brakes were better than this.
 

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SEd27

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Others with more knowledge than I can chime in, but I think you master cylinder might be too large for a single disc.

Have a look at the link below:

http://vintagebrake.com/mastercylinder.htm

Stainless lines will also give a much improved feel over rubber.

The quality control of some master cylinders can be suspect. Mine would not bleed, no mater what I did.

It turns out that one of the small passageways inside the unit was blocked.

Chased the passage with a thin strand of wire and it bled no problem after that.
 

toglhot

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The pistons are 48mm, the stock master cylinder is 5/8"or 15.8mm. I currently have a 17mm MC, so if anything the lever should move less and be harder to pull than the stock setup. To get to the ratio the table recommends, I'd have to go to a sub 13mm MC, with a ratio like that, I'd have much greater lever movement than I have now..
 

SEd27

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How did you bleed the system?

Another trick I picked up on the forum was to pop the master cylinder cover and zip tie the brake lever to the and leave over night.

This allows any small air bubbles in the system to migrate out.

I also had really good luck with a Mityvac brake bleeder. It was way more efficient/ quicker than the traditional pump the lever method.
 

toglhot

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Problem fixed. I removed the front wheel and placed a 3mm piece of steel between the pads, then bled it. It took a while, but eventually the pads contacted the bit of 3mm steel.
The problem was getting the disk between the pads. I had to use the bit of steel to prise the pads apart wide enought to fit the caliper. But it worked well, reducing the amount of lever travel and the wheel spins freely with brakes off.
 

arcticXS

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The pistons are 48mm, the stock master cylinder is 5/8"or 15.8mm. I currently have a 17mm MC, so if anything the lever should move less and be harder to pull than the stock setup. To get to the ratio the table recommends, I'd have to go to a sub 13mm MC, with a ratio like that, I'd have much greater lever movement than I have now..
A good 13 mm MC should work perfectly fine with the 72-76 caliper with opposing 48 mm pistons.
In fact, on my 74 RD350 with the exact same caliper, I use a 13 mm Brembo MC ("coffin type" reservoir), however with a ss braided teflon lined single brake line. The OEM brake light switch is no longer needed, as the Brembo MC has a switch. This setup makes for a one to two finger brake.
Unfortunately, I suspect you have air in the system, or a substandard MC, or substandard brake lines. Or any combination thereof.
I have 3 different bikes with 13 mm Brembo MC, all single disc. A Ducati M600, my XS, and my RD. The two first have 4x34 mm piston Brembo calipers, the RD 2x48 mm. Which gives very similar caliper piston area. All 3 bikes have braided hoses, and very good brakes.
 

toglhot

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Stock XS650 master cylinders are either 16 mm, or 15.8mm/5/8". Going to a 13mm would only increase lever movement and make for an easier pull. Absolutely no air in the system, and it now works fine, just needed bleeding with a thinner disk.
 

arcticXS

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Stock XS650 master cylinders are either 16 mm, or 15.8mm/5/8". Going to a 13mm would only increase lever movement and make for an easier pull. Absolutely no air in the system, and it now works fine, just needed bleeding with a thinner disk.
Yes, you are correct that the stock MC is 5/8"/ 16 mm. And that is far from optimal for a single caliper, at least when using modern, braided brake lines. (A smaller MC will increase the pressure, so more likely to "balloon" 70s style brake lines)
But my experience, and that of many others is that the optimal MC for a single 2x48 mm piston caliper is in the 12-14 mm range, depending on personal preference and mechanical leverage ratio of the MC used. I see that you suffer from arthritis, and using a smaller MC would give you a much more powerful and controllable brake. For the Brembo MC that I recommended, there are plenty of adjustable reach levers available, both from Brembo, as well as LSL and other aftermarket vendors.
 
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