master cylinder

[crazy steve]

fwiw my bike 81R and the 80 standard are fitted
with 5/8 in bores, so theyll also work without
any problems.

Pete, only the non-US bikes used those front master bore size; everything (except the LH/XJ) sold here used the larger 11/16" bore....

[cywelchjr]

Pete, only the non-US bikes used those front master bore size; everything (except the LH/XJ) sold here used the larger 11/16" bore....

So wouldn't the smaller bore used on the Euro bikes give better braking power on our brakes? I know if would give more lever movement, but if that bore size works on them, it should work fine on ours as well right?

[crazy steve]

Well, 'better' is in the eye of the beholder....

Yes, it will give higher pressure for a given hand pressure (at the cost of more lever travel) and can help the rider 'modulate' brake application a bit better. But at the end of the day, you still have the same pads rubbing against the same rotor, so IMO brake 'power' is unchanged. I'm sure some will disagree, but I feel that unless you upgrade either the pad area or the rotor area (or both), you still have pretty much the same brakes at the end of that lever....

[cywelchjr]

Well, 'better' is in the eye of the beholder....

Yes, it will give higher pressure for a given hand pressure (at the cost of more lever travel) and can help the rider 'modulate' brake application a bit better. But at the end of the day, you still have the same pads rubbing against the same rotor, so IMO brake 'power' is unchanged. I'm sure some will disagree, but I feel that unless you upgrade either the pad area or the rotor area (or both), you still have pretty much the same brakes at the end of that lever....

I would disagree, because its physics, which is not something that is open to interpretation. There are 4 ways to increase braking power.

1. Increase the clamping power of the pads against the rotors. As long as you don't melt anything this is true increase of braking power. The limitation when doing this with leverage as we have discussed is lever travel, so you can only increase it so much, but braided stainless lines can help you get a little more by removing some of the line swelling that you get with traditional rubber lines.
2. Increase pad area. This gives you more grab for the same clamping power. If you combine 1 and 2, you get even more return.
3. Increase rotor diameter in relation to wheel diameter. This actually can give more return than any of the others, but can also make braking less controllable in some cases.
4. Drilling/slotting the rotors to allow the gasses from heavy braking to escape from under the brake pads, which allows the brakes to work more efficiently.

These four methods can each be used alone, or in any combination, including all together. Frankly I've seen cars with rotors smaller than ours and brake pads about the same size as ours, they just have a bigger lever (can anybody say Vega?), now I know, they were not known for stopping well (ok, sometimes for not stopping at all) and brake life was a joke on them (I mean really a joke, I owned 3 different ones over the years and I don't think I ever had a set of front pads last longer than 9 months).

And yes, that 4th method, I've seen actual testing showing the difference in braking distance with the same brakes with drilled and slotted rotors VS non drilled and slotted rotors and it was a significant difference. And yes the testing was done with a car, but the systems in both case work the same, it's the same physics, so while the results may not be as dramatic, it would still be there.

Frankly, the only reason I can see for Yamaha putting a master cylinder with a slightly smaller bore on the European bikes is to get a little bit better braking with a very minor change to a single part of the braking system because of the much higher highway speeds run in Europe, at least back when these bikes were in production. At that time, at least in say Germany, the autobahn in most places had no speed limits. I was often passed like I was standing still when I was traveling at 110 MPH (this was in a car, I wasn't riding yet, it was right before I came back to the states and got my first bike).

They wouldn't have made that change just to make it. There must have been a verifiable advantage to the change for them to make that engineering change, because you know it cost them more to do it.

[petejw]

hi steve,

yeah i know, i put it up there in case any1 was looking
for a m/c and wanted to use the 5/8 in bore,
ive always had good front brakes and there even
better with ss lines.

[crazy steve]

...There are 4 ways to increase braking power.

1. Increase the clamping power of the pads against the rotors. As long as you don't melt anything this is true increase of braking power...

I knew I could count on you Cy....

You're right.... to a point. Yes, higher pressure translates into the pads being pressed against the rotor harder and more energy being scrubbed off, but the limiting factor is controlling the bike. If you apply enough pressure, the rotor stops turning and you'll either have the front tire wash out or go ass over teakettle. Seeing how the stock brakes can be locked up, I don't see much benefit from adding pressure. It's not the added pressure of the smaller master that gives the 'increase', it's the fact of a less 'sensitive' action that will give you a bit more control in modulating brake application, but I think a skilled rider could get the same braking results either way. Exact same effect as braided lines; a better 'feel'.

Brakes convert kinetic energy into heat, so the real trick is to dissipate the heat as quickly as possible. Option one does nothing for that, while 2 through 4 do....

[petejw]

i havent got a 11/16 m/c to compare,
but from what ive read on here with a lot of
ppl having lack of good lever pressure, with my m/c
and the old rubber lines, the bike stopped
really well, even better with ss lines. there
isnt much travel in the lever either.

[eepmep]

sponge cleaning

I've had problems with the sponge hole getting clogged. I clean it and it works good for a bit then the its back to the breaks sticking. Would flushing the break lines fix this?

[crazy steve]

I've had problems with the sponge hole getting clogged. I clean it and it works good for a bit then the its back to the brakes sticking. Would flushing the brake lines fix this?

If you've got enough 'stuff' in there that the problem keeps coming back, I'd recommend disassembling the whole brake system (master cylinders, calipers) and thoroughly clean them out. Flushing might do it, but the only sure cure is a cleaning...

[cywelchjr]

But if you have that much crud in there, you might have the inside of the rubber hoses coming apart, which can only be fixed by replacing them, preferably with braided stainless lines.

[bikemight]

So I ended up putting the mikes xs 16mm bore master on my '80 mns. It works great! I also replaced the bars with a superbike bar style. Way more comfortable and not to mention look way better. I'll need to get a new shorter throttle and clutch cable at some point but it's fine for now. This bike is like a dream compared to my cb500t. Thanks again for all the response.

[jwhughes3]

I have the 16mm

On my 80 Special for awhile from Mikes and no issues.

John

[Nubian]

reviving old thread

Would not the bore size on the calipers also have to be reduced to 5/8 to increase the pressure applied to pads?

I would disagree, because its physics, which is not something that is open to interpretation. There are 4 ways to increase braking power.

1. Increase the clamping power of the pads against the rotors. As long as you don't melt anything this is true increase of braking power. The limitation when doing this with leverage as we have discussed is lever travel, so you can only increase it so much, but braided stainless lines can help you get a little more by removing some of the line swelling that you get with traditional rubber lines.
2. Increase pad area. This gives you more grab for the same clamping power. If you combine 1 and 2, you get even more return.
3. Increase rotor diameter in relation to wheel diameter. This actually can give more return than any of the others, but can also make braking less controllable in some cases.
4. Drilling/slotting the rotors to allow the gasses from heavy braking to escape from under the brake pads, which allows the brakes to work more efficiently.

These four methods can each be used alone, or in any combination, including all together. Frankly I've seen cars with rotors smaller than ours and brake pads about the same size as ours, they just have a bigger lever (can anybody say Vega?), now I know, they were not known for stopping well (ok, sometimes for not stopping at all) and brake life was a joke on them (I mean really a joke, I owned 3 different ones over the years and I don't think I ever had a set of front pads last longer than 9 months).

And yes, that 4th method, I've seen actual testing showing the difference in braking distance with the same brakes with drilled and slotted rotors VS non drilled and slotted rotors and it was a significant difference. And yes the testing was done with a car, but the systems in both case work the same, it's the same physics, so while the results may not be as dramatic, it would still be there.

Frankly, the only reason I can see for Yamaha putting a master cylinder with a slightly smaller bore on the European bikes is to get a little bit better braking with a very minor change to a single part of the braking system because of the much higher highway speeds run in Europe, at least back when these bikes were in production. At that time, at least in say Germany, the autobahn in most places had no speed limits. I was often passed like I was standing still when I was traveling at 110 MPH (this was in a car, I wasn't riding yet, it was right before I came back to the states and got my first bike).

They wouldn't have made that change just to make it. There must have been a verifiable advantage to the change for them to make that engineering change, because you know it cost them more to do it.

[cywelchjr]

Would not the bore size on the calipers also have to be reduced to 5/8 to increase the pressure applied to pads?

No, the MC piston and caliber pistons are different sizes anyways. That's how the brakes work. If they were the same size you wouldn't be able to stop the bike.

[Nubian]

No, the MC piston and caliber pistons are different sizes anyways. That's how the brakes work. If they were the same size you wouldn't be able to stop the bike.

Well I guess I will seek out a euro standard m/c front and rear and hopefully improve braking. Same size fittings on the euro model?