Topic: 1976 550cb ft reservoir ? about bore size

[jjc]

I have put duel front rotors on my bike and can't seem to get the lines bleed. Standard reservoir dia is 1/2". I would like to increase that. What's the next size up,7/8?, Can't remember. But anyway I figure the larger bore will move more fluid making the lever having to move less & perhaps i can get the system bleed easier.

 I have worked on a lot of bleeding jobs but this time I'm just circulating fluid w/o getting anything to firm up.
My question is this and it's only to the guys that have changed there ft master cylinder to a larger size.
   
 I'm having a hard time finding a unit with a larger bore that will match the left lever set up the best. I don't mined going to a square reservoir & I need all black lever with the hose connection on the  reservoir to the front.
Presently running a Nissin 1/2" bore. Looks good but 1/2, no. I want 7/8" I think the next size is.

What's out there to look at???

[scottly]

The stock master cylinder has a 14mm bore, and works VERY well with dual calipers and rotors.

[calj737]

Depending upon how your second brake line or split line is routed, you may be trapping air above the tire. It’s been my experience to bleed the caliper farthest from the MC first. And I’ve had bikes that required removing the caliper due to bleeder position or routing of the lines.

And as Scottly said, the stock works perfectly well for dual calipers.

[bryanj]

Many years ago i did a twin dis 500 and it had long lever travel so fitted a GL 1000 master and it worked perfectly

[newday777]

I have put duel front rotors on my bike and can't seem to get the lines bleed. Standard reservoir dia is 1/2". I would like to increase that. What's the next size up,7/8?, Can't remember. But anyway I figure the larger bore will move more fluid making the lever having to move less & perhaps i can get the system bleed easier.

 I have worked on a lot of bleeding jobs but this time I'm just circulating fluid w/o getting anything to firm up.
My question is this and it's only to the guys that have changed there ft master cylinder to a larger size.
   
 I'm having a hard time finding a unit with a larger bore that will match the left lever set up the best. I don't mined going to a square reservoir & I need all black lever with the hose connection on the  reservoir to the front.
Presently running a Nissin 1/2" bore. Looks good but 1/2, no. I want 7/8" I think the next size is.

What's out there to look at???

Your problem is you still have air trapped in the lines.

You are thinking wrong on going to a bigger bore master is the answer to your problem. 
Read the facts below in the link.
I worked at a Trike shop and learned about this from my friend who has a engineering degree and a mind to go with the degree. There is science in hydraulics.

"Bigger master cylinder
If you increase the size of the master cylinder, you will actually be REDUCING the power of the brakes. Yes, with a bigger master cylinder, you will have to squeeze HARDER to get the same braking force at the calipers. This is because you are reducing the hydraulic advantage you have over the calipers. Crazy, right? Maybe but it's still a fact."

https://www.customfighters.com/threads/matching-a-front-master-cylinder-to-your-caliper-s.56704/

[jjc]

Well my original reservoir was bad and I had Nissen 1/2 bore around so I'm using that for now. As for routing the lines. I'm using two lines. Each caliper has it's own line right up to the reservoir.
I have hit the lines lightly as I was bleeding. Initially I filled the reservoir from the calipers up by squirting fluid in the caliper until it showed in the reservoir. I have used a hand vac to suck fluid from the calipers from then on. Man, I'm not getting any air out and the fluid just circles through. I'm on my sec bottle now. Fill pump fill nothing is changing. Lever goes to the bar.

Question - I don't have a vac pump that uses an air hose hooked to it. A anybody suggest getting one of those. Not sure if one would work better than a hand vac

[newday777]

Did you 1st bleed the master cylinder at the banjo bolt before bleeding the calipers? Very needed.

[scottly]

A 1/2" bore is only 12.7mm, which can be used to improve a single caliper setup, but might be too small with your dual system: I've never tried that particular combo, but can confirm that 14mm works. Is there any resistance at all when pulling the lever to the bar? Have you actually tried the brakes on the road? You just might find that the brakes work so well that you will never have to squeeze the lever hard enough to get to the bar.

[spotty]

The stock master cylinder has a 14mm bore, and works VERY well with dual calipers and rotors.

ooooh, i replied to this post but i've been deleted, did i upset someone ? thats made my day that has. all i asked was define VERY well

[scottly]

The stock master cylinder has a 14mm bore, and works VERY well with dual calipers and rotors.

ooooh, i replied to this post but i've been deleted, did i upset someone ? thats made my day that has. all i asked was define VERY well

Huh?? What chu talkin bout??

[spotty]

The stock master cylinder has a 14mm bore, and works VERY well with dual calipers and rotors.

ooooh, i replied to this post but i've been deleted, did i upset someone ? thats made my day that has. all i asked was define VERY well

Huh?? What chu talkin bout??

surprised me too , i've written some right stupid things on here and yesterday was actually just a ( i thought) valid question, ah well, i'll survive

[scottly]

Well, in any case, VERY well means just that, with the emphasis on very. With 2 38mm calipers, the stock 14mm MC is just about ideal. With 2 42.8mm calipers (used on the early F and late K) the 14mm is almost on the small side, making for a lot of lever travel, but still works well. Honda F-d up with the late F and Goldwings by using a huge 17.5mm master with 2 38mm calipers.

[scottly]

A 1/2" bore is only 12.7mm, which can be used to improve a single caliper setup, but might be too small with your dual system: I've never tried that particular combo, but can confirm that 14mm works. Is there any resistance at all when pulling the lever to the bar? Have you actually tried the brakes on the road? You just might find that the brakes work so well that you will never have to squeeze the lever hard enough to get to the bar.

[jjc]

Getting back to brake problem since it's summer -
duel brakes, just like stock put on right. Both calipers on top. Bought all stock pats for rt and the conversion part for the epeedo and there is action on both sides, just not pumping up.
Action,not excessive wiggling.Did have to much wiggling on the rt, but fixed it.

I do not have enough brakes on the front to ride it.
still have / using the 1/2" bore master.
have used a 1/2" bore on a duel conversion  before, but know that 9/16 helps move the lever less to activate. Yes it may need more pressure to stop, but the lever travels less.

Have still been cycling fluid w/o getting any decent pressure. Yes some pressure, but not enough to ride it.

Oh
I'm using a hand pump, Any other better for - MY issue?

[jjc]

Newday777 asked before about bleeding at  the master,  but I do not have a bleed port at the master.  I did add fluid from the bottom (injected with a syringe) at the start til it showed at the master

[scottly]

If you have the adjusting screws and springs installed, remove them for now. Try reverse bleeding by pushing the pistons, one at a time, back into the caliper. Make sure the the line is at the top of the caliper as you do this, so any air that is trapped goes up the line. Be aware that the fluid will be forced up into the master reservoir, so watch that it doesn't overflow. After you do one side, pump the lever to return that piston back out before going to the other side.

[bryanj]

I have written up several times about bleeding the master cylinder please use the search function

[Bankerdanny]

Randakk had some thoughts on this issue over at his business site before he retired. His view was that the twin disk bikes should use a 5/8" piston. When I put the F3 front end on my F1, I installed a 5/8" Nissin radial master. I have great feel and 2 finger braking.

[scottly]

And, as I've stated many times before, the stock 14mm MC works VERY WELL with 2 38mm calipers. BTW, Kawasaki did use a 5/8 MC with 2 42.8mm calipers.

[Oddjob]

You could try testing the master cylinder to see if the fault lies there.

Remove the brake lines and use a suitable bolt and washer to seal off the hole where the lines go. Then try pulling the lever, it should go rock hard, if it doesn't the MC is airlocked somewhere, check to see if the really small hole in the reservoir isn't blocked, try doing really small movements of the lever whilst watching that hole, any air bubbles mean it's starting to bleed up OR it means the piston seal is leaking allowing air into the system everytime it's operated.

Report back.

[bryanj]

If 14mm was ok why did Honda used bigger on the GL 1000 that has same caliper piston bore

[scottly]

If 14mm was ok why did Honda used bigger on the GL 1000 that has same caliper piston bore

Like I said in reply 11, Honda F-d up on the GL and late F. Why? Maybe for the same reason they used a 14mm for a single 38mm caliper, when a 1/2" would have been a better fit?

[newday777]

Newday777 asked before about bleeding at  the master,  but I do not have a bleed port at the master.  I did add fluid from the bottom (injected with a syringe) at the start til it showed at the master

Just use the banjo bolt at the master. Put rags under the master to help catch the fluid. Protect all painted parts! Pump up, hold, open banjo bolt  as if bleeder valve.  Repeat a couple times.

[pekingduck]

If you have too mkuch air inthe lines, it may be impossible to bleed the system.  I have had great success initially bleeding a brake system by removing any fluid in the reservoir by soaking it up in a paper towel, then pushing the caliper pads in all the way, back-filling the reservoir.  This moves a lot of fluid very quickly, bringing any trapped bubbles from below.
I then soak that fluid out, fill with fresh fluid, and pump up to full pressure by hand, and break open the bleeder valve to get any residual old fluid in the system.

As to what size master cylinder for what size caliper, I would use an 11mm or 12mm or at most, a 1/2" on a single piston caliper.  When disc brakes were new in the '70s, everyone was afraid of locking up the front brake, but now, 11mm and 12mm masters are the norm on single/double pistons.

Here is an interesting article and chart for piston area/master cylinder bore.

http://www.vintagebrake.com/mastercylinder.htm

[jjc]

Well put about ten bowls of fluid through each side of the ft yesterday and got no where. I have another master in the way so will try that and messing with the pads when it gets here

[jjc]

Well I got tired of doing the same thing w/o any changes. So I got another master cylinder,mounted it & pushed back the pads on each side. Unfortunately, results were the same. I ran about 6-7 bowls of fluid through but stall can't get a hard lever. I get a somewhat firm lever, but it still goes to the bars. Looks like this bike is not going to get on the road unless I unplumb the right disc & just run the original right. Just leave the rt disc on for looks.

[Oddjob]

Just remembered something. Someone with a similar problem, turned out to be the brake light switch, it was allowing air to enter to line every time the lever was pulled. It wasn’t the sealing washer, it was sucking air through the plastic seal on the back where the contacts are. Might just be your problem as well.

[jjc]

Don't quit under stand this but I now have a new 5/8 master so I would not have that issue now,right? Being I'm running a new switch with the new master
.

[scottly]

Please post some pics of how your system is set up.

[Oddjob]

Stupid question but is there a sealing washer between the 2 banjos on the MC? As in, sealing washer, banjo, sealing washer, banjo, sealing washer, banjo bolt.

The leaking pressure switch was on a standard dual system running one line down to the splitter on the bottom yoke and 2 lines running off that, didn't notice you were running 2 lines from the MC.

[jjc]

Up date
Trouble continued until I got back to Geoffrey's Garage back east (from me) and got off the 'everything should be fine with alignment of my new rt side brake system because I eliminated that pesky fender mount that was getting in the way & everything else on the right is stock parts' thought. And on to the thought 'something could still be woong with the alignment because of manufacturing spects and the fact they never intended for anyone to put a brake on the right side thought'.So I got out my 6" metal ruler and after removing the right pod, I laid it up against the rotor and rotor arm to check alignment. Yep it was off enough to make the pads bind or sponge/wiggle back & forth,but never come straight down on the rotor and seat firmly when trying to breed the system. It also became apparent that the right side had an issue when I unhooked the right side and was able to pump up the brakes in just five minutes.
So I started shimming the arm mounting points until I got the arm to be inline with the disc according to my little ruler. In about an hr later the system pumped up and I was done. Waisted all that time thinking that tolerances would be fine because I had all stock parts on the right as I did on the left.

[Bankerdanny]

Good job sorting it out. It is frustrating when you finally do and it is something simple.

[scottly]

'everything should be fine with alignment of my new rt side brake system because I eliminated that pesky fender mount that was getting in the way & everything else on the right is stock parts' thought

The fender brace fits under the right side caliper mount, and acts as the spacer.

[jjc]

Well thought I was done after getting a good solid lever,but on a ride I found out that sometimes when pulled it is solid and then other times much lower firmness or it pumps up after 3-4 pulls. Obviously that's an issue but I am not sure what's going on.
Tried bleeding again but o air came out. So eighty miles on the road now, but issues.

[scottly]

Sounds like a brake piston may be slowly getting pushed in, which is why you have to pump the lever to push it back out? A member recently reported the hard line to the caliper was bent, which caused the inside pad to be pressed against the rotor, which would be the opposite in your case. You might try fitting the adjuster and spring now, starting with the right side caliper, as it will limit how far the caliper moves inward.