Topic: dual brake...where to buy?

[Loki]

hey there everyone, im going to be putting dual disks on my cb 550. i looked for parts to do it off a 750 or something but i havent been able to find any, if any of you guys could direct me to a site or somewhere to buy what i need id appreciate it. thanks!

[754]

I have a Caliper, Hanger, and disc..it  may need a piston.

[ev0lve]

hey there everyone, im going to be putting dual disks on my cb 550. i looked for parts to do it off a 750 or something but i havent been able to find any, if any of you guys could direct me to a site or somewhere to buy what i need id appreciate it. thanks!

I got my caliper, line and hanger from a member here (it's a good route to go as opposed to eBay) and the disk from eBay but I don't think there are any sites selling the bits as a conversion.

BTW, the 750/550 rotors are different diameters. Be sure of what you're getting if you're going to try and mix and match.

[Loki]

ya im aware they are different im staying with the 550 rotors but i need the reservoir from a 750 dual disk brake bike. correct me if im wrong but thats what iv read in some of the threads on this site. maybe i only need a reservoir from a 750 single disk. .....so 754 if you have that then we can talk a bit more. thanks

[Laminar]

The reservoir from a Goldwing GL1000/GL1100 is also an option.

[ev0lve]

Yup, I just finished mine with the stock master cylinder and the throw on the lever is VERY long. Supposedly the MC from any dual disk machine will work with the details of why concerning the piston size. Do a search. Lots of info on the specifics.

[754]

kre-eper, PM me if interested, we are both in Canada. Someone els, is asking if you dont need them
 I ran dual disc on 750 with stock MC, and never could figure what the fuss was about changing master sizes?

[ev0lve]

kre-eper, PM me if interested, we are both in Canada. Someone els, is asking if you dont need them
 I ran dual disc on 750 with stock MC, and never could figure what the fuss was about changing master sizes?

Reading about it the smaller piston has to move farther to displace the same increased amount of fluid. That's all there is too it as I understand it. The practical upshot is you get something like this with a stock 750 MC.


Unless yours is different then I'd be pretty interested in how?

[754]

I had braided -3 lines I made. I think rubber lines may have worse feel.

 I remember scaring the crap outa myself when I had the tire hopping & chirping at about 70mph..

 If I remember, and its been years, it was not an inordinate amount of effort I had to apply, nor do I remember it being that close to grip.

 Fwiw, try it if you dont have the other size, then change it out later if you dont like.

 One thing i learned, way back, was to tap the lines with a wrench, from bottom up to top, to male bubbles let go and rise, may make a BIG difference.

 Prior to the late 70,s, I bet there was at least 500 people in North America, running dual disc with stock mc..

[fishhead]

Even the Goldwing Dual disc front end benifits from a smaller master cylinder.

http://www.randakks.com/Brake%20Parts.htm

I've used both the stock CB 750 master cylinder and the GL 1000 master cylinder (both dual disc with braided brake lines) and while there is more travel in the stock CB master cylinder, there is also more modulation with the stock CB master cylinder.
  With the "extra" travel with the stock CB master cylinder, it also gives a more precise feel to the front brakes.
 The GL 1000 master cylinder gave a "wooden" feel to the GL and it will also give a "wooden" feel to the dual disc CB.

[Loki]

thanks for all the info but i still think im going to stick with a cb 750 brake reservoir.... but like i asked before do i need to use a dual disk one or will a singe disk reservoir work from a cb 750?

[ev0lve]

Only having the bike out on the road for a couple days the stock MC is adequate I think. I've got SS lines as well and tried to make sure I have all the air out of it (there's one loop between the MC and the brake switch I tried to make sure was clear mounting the MC on another set of bars and straightening the line out vertically) and that's the best it will do.

MC was rebuilt and it does start to grab almost immediately but doesn't seem to want to apply as much pressure as I think it should. Only way I'll know though is to replace it with a larger piston MC so some penny saving is in order 

[ev0lve]

thanks for all the info but i still think im going to stick with a cb 750 brake reservoir.... but like i asked before do i need to use a dual disk one or will a singe disk reservoir work from a cb 750?

They'll both work. Just depends on what you want out of it. Whatever you end up doing post back when you're done so we'll know how it worked out 

[Laminar]

Reading about it the smaller piston has to move farther to displace the same amount of fluid. That's all there is too it as I understand it.

Almost. The braking system follows simple hydraulic principles:



Pushing one piston down displaces fluid and forces the other piston up. Pushing the left piston down to the bottom dotted line would push the right piston up to the upper dotted line.

This is how your brakes work - the master cylinder is mounted on your handlebars. When you pull the brake lever, the piston in the MC pushes brake fluid through the brake lines and into the caliper. That fluid then pushes the brake pistons against the brake pad, squeezing the brake rotor.

Switching from a single caliper to a dual caliper system is like adding a third piston to the above diagram. Suddenly, pushing one piston down to the bottom dotted line would only displace enough fluid to push the other two pistons halfway up to the top dotted line. This is why if you're using a stock MC designed for use with a single caliper, you suddenly have to pull the brake much farther to fully apply the brakes. Now imagine replacing the leftmost piston in the diagram with a bigger piston - one with twice as much surface area. Now, pushing that bigger piston down pushes out more fluid per distance travelled, and that fluid is able to move the other two pistons more quickly than before.

So it's not that the MC's piston has to travel more to displace the same amount of fluid, but the MC's piston has to displace more fluid with dual calipers, so it has to be pushed further.

[ev0lve]

Well, that's what I meant to say of course 

[754]

Does smaller ID of lines factor in..??

[Laminar]

Does smaller ID of lines factor in..??

I'd lean towards no.



Imagine the reservoir connecting the two pistons represents the brake lines. Now imagine it's four times bigger. When one piston is pushed down, there's still only one place for that extra fluid to go - the other piston.

Assuming the fluid is incompressible (good assumption) and that the brake lines don't expand at all (poor assumption with rubber, better with braided steel), the only difference installing larger ID brakes lines makes is total brake fluid volume - it shouldn't affect brake lever throw.

[754]

I dont think like most people.. so when I explore a concept, I tend to go to extreme examples to better understand (simplify)the problem to be solved.

 So consider this;
 The master cyl volume produced by  a certain range of movement is constant..
 Lets say it pumps 25cc from at rest to touching the bar (figure pulled out of a hat, but it remains constant regardless of the actual number)

 still with me?

 So now picture a brake line with a 1 inch ID, and one with a .040 thou ID (1mm). Now, which should push the caliper (or calipers) further?, given that the amount, it is able to move remains constant regardless of brake line size?

..............................................................................
So i am thinking a smaller or more rigid line will be more responsive..

[Laminar]

I dont think like most people.. so when I explore a concept, I tend to go to extreme examples to better understand (simplify)the problem to be solved.

 So consider this;
 The master cyl volume produced by  a certain range of movement is constant..
 Lets say it pumps 25cc from at rest to touching the bar (figure pulled out of a hat, but it remains constant regardless of the actual number)

 still with me?

 So now picture a brake line with a 1 inch ID, and one with a .040 thou ID (1mm). Now, which should push the caliper (or calipers) further?, given that the amount, it is able to move remains constant regardless of brake line size?

In both cases, 25cc of brake fluid go into one end, and 25cc of brake fluid come out the other.

So i am thinking a smaller or more rigid line will be more responsive..

A more rigid line will be more responsive. Imagine an extreme scenario - the brake line is made from water balloon material. When you squeeze the brake lever, instead of the fluid pushing the caliper's pistons into the brake pad, the "balloon" just grows and expands. When you let off the brake, it deflates. This is essentially what happens with rubber brake lines - some of the force exerted by the fluid is wasted by expanding brake lines. Now imagine trying to inflate a balloon made of steel. Not possible - that's why rigid brake lines are better.

I'd still posit that brake line diameter has nothing to do with lever throw distance.

[mystic_1]

A smaller line will have some effect though, it won't move fluid as fast so there will be resistance to fluid flow.  So, the lever may FEEL firmer, but only because you're trying to squeeze the same amount of fluid through a smaller line.  Result, slower braking action.

mystic_1

[Laminar]

A smaller line will have some effect though, it won't move fluid as fast so there will be resistance to fluid flow.  So, the lever may FEEL firmer, but only because you're trying to squeeze the same amount of fluid through a smaller line.  Result, slower braking action.

mystic_1

Yep. Same lever travel, but harder to pull. Just like drinking through a coffee stirrer vs. drinking through a regular straw.

[754]

I agree it would be more restrictive, wether or not you can feel the difference is the issue at hand.

I have heard for years the rubber lines give or swell a bit resulting in a softer feel. On braided lines that you buy, smaller seems  to be the norm now, years ago -4 was pretty common.

[Loki]

this has all been great from all of you and i do appreciate it but i have still not had an answer about where i could buy the bigger mc.....does any one have one for sale?..

[ev0lve]

This is the one I'm eyeballing at this point

http://cgi.ebay.com/ebaymotors/FRONT-BRAKE-MASTER-CYLINDER-CB650-CB750-CB900-NIGHTHAWK_W0QQcmdZViewItemQQcategoryZ35592QQihZ004QQitemZ140317265545QQrdZ1QQsspagenameZWDVW

Yoyodyne
http://www.yoyodyneti.com/Category.aspx?CategoryID=3006

And plenty more to look at. Google is your friend.
http://www.google.com/search?client=safari&rls=en-us&q=motorcycle+master+cylinder&ie=UTF-8&oe=UTF-8

Try it yourself by using the Google code to search the site if your looking to dig up more info from here

site:forums.sohc4.net your search terms

But the best info I can find is that the caliper piston is 38mm and the stock MC piston is 11mm 14mm so according to this chart from
http://www.vintagebrake.com/mastercylinder.htm


I want a 15mm 5/8ths piston in the next master cylinder I buy but a 16mm would do.

Anyways, any MC from a dual up bike should work used or new depending on the piston size. I've had very poor luck getting a working non-mangled cheapie off of eBay. Maybe your luck is better.

Maybe some of our resident engineers will chime in (please!)

[Loki]

thanks alot! im probly going to run the stock size caliper on the bike seeing how i already have two of them. all i need is the ms and a 1 into 2 hose connect, but im going to be going with braided lines so i think when i buy them ill just also buy a 1 into 2 adapter.