Where does your brake lever stop?

[Norton7d]

Does it stop well before the grip, and get progressively harder along the way?
Or does it go all the way to the grip, with little increase in resistance even though the front pads are firmly placed against the rotor?

New pads, new SS brake line, new MC that MM assures me is appropriate, even though 5T questions the small bore on a.twin piston caliper.

Thanks

 

[Jim]

I'm running a stock master and dual disc conversion. I can pull it all the way to the grip fairly easily. Of course, the wheel will lock long before I get there.

 

[member28833]

Or does it go all the way to the grip, with little increase in resistance even though the front pads are firmly placed against the rotor?

Nope.

 

[member28833]

Hoping that you just have air still in the system

 

[Skip]

I have a stock master cylinder with dual disc brakes with rubber brake hoses and my lever is about 3/8" away from the grip

 

[member28833]

Skip, that would be a stock XS Special master cylinder?

 

[Skip]

Skip, that would be a stock XS Special master cylinder?

Yes it is

 

[member28833]

3 known examples of dual disk stock Special master equipped XS's
Norton7d yours is a different case. 76 calipers? And a different mc too.?

 

[Skip]

Back when I installed the dual disc , I researched the debate about the MC size...I chose to first give the stock MC a shot.
Nice smooth 2 finger pull , progressively to a strong hard end about 3/8 " from the grip.
That ended the debate for me...

 

[Norton7d]

I am running the twi. Piston 76 caliper, with the 12.9 bore MC.
My lever is like Jim's, not much feel and goes all the way to the handle

 

[5twins]

Well, in my opinion, you've gone a little too small on the MC. Smaller than the old original stock sizes does work better, but only very slightly smaller seems best. On my later systems, 14mm is stock and most say get an 11mm, so I did. Frankly, I'm not that impressed. It's like yours, pulling to the bar under sustained pressure. The lever also pulls about 1/4 to 1/3 through it's travel before much of anything happens. It does give better feel and more progressive engagement, but I don't like all that extra lever travel. So, on my other 650, I decided to go only a little smaller, to a 1/2" (12.7mm). I think this one works great, much better than the 11mm. It gives the benefits of the 11mm (better feel and more progressive engagement) but with much less lever travel, not much more than the old stock 14mm MC.

So, I think you'd benefit from a MC just slightly smaller than stock. I think your stock one was 16mm or 5/8". I'll bet the stock 14mm size from the later model would work well for you, most certainly better than the 12.9mm you have on there now.

 

[Norton7d]

Thanks 5T, I will give it a bit more time to grow on me, if not happy, I will switch to something larger like you suggest.
Do you know of something offered as new that is plug and play for me?
I also need to check my rotor for run-out, as my lever has a bit of "pulsating" feel when I apply the brake thus leading to the possibility my rotor has a bit of warp to it.

 

[5twins]

I don't have a new one I could suggest but the originals are plentiful and a dime a dozen. You could probably get one in nice shape for not too much money. I'll admit, I'm a cheap S.O.B. Both of my smaller MCs came used and cheap off eBay (less than $20 each). Yes, you take a chance on used, but if in good shape they shouldn't need much more than a disassembly and cleaning. And if worse comes to worse, maybe a rebuild kit. Both of mine are genuine Yamaha units from other models so are good quality. I would rather use these than even a new China one.

 

[arcticXS]

Does it stop well before the grip, and get progressively harder along the way?
Or does it go all the way to the grip, with little increase in resistance even though the front pads are firmly placed against the rotor?

New pads, new SS brake line, new MC that MM assures me is appropriate, even though 5T questions the small bore on a.twin piston caliper.

Thanks

The way I read your post, you have a single disc with the older dual 48 mm piston caliper, 76 and earlier. Is this correct?
(Some posters talk about two disc setup here, confusing the issue)

My XS is a 77, but my RD350A has the exact same caliper as 72-76 XS/TX, combined with a new teflon/ss braided line and a 13 mm Brembo master cylinder. This works much better than the stock 5/8" mc. Both with the stock cast iron caliper, and the alloy reproduction I'm currently using (which supposedly is less rigid than the oem iron version)
With either type calipers, the lever does not come all the way to the grip. As I often brake with two fingers, that would not be a good thing...
Also, a buddy had a Grimeca 1/2" mc on his RD, it worked great as well.
Both these match well with the recommendations from MM/ Vintage Brake. That table on the Vintage Brake website is spot on IMHO.

So, regarding your issue, you may have one of three problems:
-Air bubbles somewhere in the system. Bleeding can take a lot of time and effort
-A faulty or low quality master cylinder. You did not state what brand you have...At least theoretically, the mechanical leverage ratio may be too high compared to brand name master cylinders with the same bore. Put differently, all 13 mm master cylinders are not created equal.
-Or you have installed those "anti squeal" shims behind your pads. With these installed, I never managed to get a firm brake lever on the RD. And the brake never squeals without them anyway. So bin them if you have them!

 

[Paul Sutton]

When considering a new MC with a smaller piston many refer to the Vintage Brake article and the "wooden" feel:
https://www.vintagebrake.com/mastercylinder.htm
The key part in understanding hydraulics is the ratio of the MC Piston Area to the Total Slave Cylinder Piston Area. Since we are dealing with round pistons the Area = Pi x Radius x Radius. An alternative way to view this is to just look at the ratios of the MC Diameter Squared.

Example 1: XS650SH has a 14mm MC. If I change to a 12.7mm MC the area ratio is (14 x 14)/(12.7 x 12.7) = 1.22
I call this a 22% change. It leads to an improvement in the braking with less effort required and no sponginess at the perch. The 12.7mm gives a similar travel to 14mm and we would expect this because it is a small change in surface area.

Example 2: XS650SH has a 14mm MC. If I change to an 11mm MC the area ratio is (14 x 14)/(11 x 11) = 1.62
I call this a 62% change, quite big. It leads to big changes in braking, lever feel and lever travel. Is this a good change? Some love it and some hate it. This is because a change from 14mm to 11mm represents a significant change in surface area.

Example 3: Virago XV1000 has a 16mm MC. If I change to a 14mm MC the area ratio is (16 x 16)/(14 x 14) = 1.31
I call this a 31% change and feels similar to Example 1 above.

Example 4: In changing from a 16mm MC to a 12.9mm MC the change is (16 x 16)/(12.9 x 12.9) = 1.54
I call this a 54% change, quite big. This change is similar to Example 2, but I would have expected a little less lever travel.


My preference, which is mine alone, is to stay above a ratio of 1.40. If a change from 16mm to 12.9mm is not comfortable the ratio of 1.40 would suggest an MC greater than or equal to 13.5mm i.e. 14mm as previously suggested by 5twins.

 

[Norton7d]

The way I read your post, you have a single disc with the older dual 48 mm piston caliper, 76 and earlier. Is this correct?
(Some posters talk about two disc setup here, confusing the issue)
My XS is a 77, but my RD350A has the exact same caliper as 72-76 XS/TX, combined with a new teflon/ss braided line and a 13 mm Brembo master cylinder. This works much better than the stock 5/8" mc. Both with the stock cast iron caliper, and the alloy reproduction I'm currently using (which supposedly is less rigid than the oem iron version)
With either type calipers, the lever does not come all the way to the grip. As I often brake with two fingers, that would not be a good thing...
Also, a buddy had a Grimeca 1/2" mc on his RD, it worked great as well.
Both these match well with the recommendations from MM/ Vintage Brake. That table on the Vintage Brake website is spot on IMHO.

So, regarding your issue, you may have one of three problems:
-Air bubbles somewhere in the system. Bleeding can take a lot of time and effort
-A faulty or low quality master cylinder. You did not state what brand you have...At least theoretically, the mechanical leverage ratio may be too high compared to brand name master cylinders with the same bore. Put differently, all 13 mm master cylinders are not created equal.
-Or you have installed those "anti squeal" shims behind your pads. With these installed, I never managed to get a firm brake lever on the RD. And the brake never squeals without them anyway. So bin them if you have them!

76 single caliper, single disk.
Yes, i do I assume no air bubbles, no reason to assume air is still in line.
The anti squeal shims are in place, maybe I will remove and see if the lever improves any.
Thanks for the suggestion.

 

[Norton7d]

The way I read your post, you have a single disc with the older dual 48 mm piston caliper, 76 and earlier. Is this correct?
(Some posters talk about two disc setup here, confusing the issue)

My XS is a 77, but my RD350A has the exact same caliper as 72-76 XS/TX, combined with a new teflon/ss braided line and a 13 mm Brembo master cylinder. This works much better than the stock 5/8" mc. Both with the stock cast iron caliper, and the alloy reproduction I'm currently using (which supposedly is less rigid than the oem iron version)
With either type calipers, the lever does not come all the way to the grip. As I often brake with two fingers, that would not be a good thing...
Also, a buddy had a Grimeca 1/2" mc on his RD, it worked great as well.
Both these match well with the recommendations from MM/ Vintage Brake. That table on the Vintage Brake website is spot on IMHO.

So, regarding your issue, you may have one of three problems:
-Air bubbles somewhere in the system. Bleeding can take a lot of time and effort
-A faulty or low quality master cylinder. You did not state what brand you have...At least theoretically, the mechanical leverage ratio may be too high compared to brand name master cylinders with the same bore. Put differently, all 13 mm master cylinders are not created equal.
-Or you have installed those "anti squeal" shims behind your pads. With these installed, I never managed to get a firm brake lever on the RD. And the brake never squeals without them anyway. So bin them if you have them!

76 single caliper, single disk.
Yes, i do I assume no air bubbles.
The anti squeal shims are in place, maybe I will remove and see if the lever improves any.
Thanks for the suggestion.

 

[5twins]

I very much like Paul's method of figuring out the amount of change a different size MC will have. It is much easier to understand than that chart from 3M, and seems to agree better with what I found with the two smaller sizes I have tried. According to 3M's chart, the 1/2" MC I really like falls well out of the ratio range he considers ideal for a single piston caliper. Going by his chart, I probably wouldn't have even considered it had I not already tried the 11mm and found it so lacking (in my opinion). I figured a size about midway between the 11mm and the 14mm might work better, and I feel it has.

 

[member28833]

Whats catching my eye lately for my 78E are those early 90's FZR 600 dual gold calipers with opposing pistons. They look sharp and I've wondered how simple it "could be" to hang those on hangers using the stock XS forks and 5mm rotors.

 

[arcticXS]

I believe the early XS/RD calipers are hard to beat for pure clamping force from a classic style caliper. Few other calipers have larger bore, most are significantly smaller, like the popular AP Lockheed 41 mm and Brembo 38 mm.
Brembo had some in 48 mm, but they are very hard to find.
The downside is the wide swept area, resulting in a heavy disc.