Putting An ABSII Front End On A Standard ST1100

[Larry Fine]

Once the pads engage the discs, there should be very little additional travel. Perhaps only one disc is being grabbed, and the other has additional travel that is preventing the firm lever.

Are we sure all of the caliper cylinders are full of fluid?

If I may make a suggestion, just from my own understanding, but please make sure it's not a bad idea?

Now that the calipers are as full as they are, what about removing each one at a time, and using the pads or other spacers to make sure no pistons pop out, squeeze the pistons back into the calipers as a form of bottom-to-top bleeding.

As long as the volume of the calipers exceeds the volume of the lines including fittings, the lines should be fully air free.

The MC should be level and the fluid level be kept low and watched to avoid spills, and protection provided anyway. Any air left in the caliper cylinders would be at the top area, which should bleed more easily.

Logical?

 

[ST Gui]

pumping 6 pistons instead of 4

+1 I have been following all 73 posts but haven't retained much. But if it is the same master cylinder moving two extra pistons than designed for that means less effort and more lever travel and most likely less maximum braking..

This is the problem I had when I converted my 750-4 to dual disk. The brake lever had almost no resistance and when straight to the grip.This was after bleeding the brakes. I replaced the factory lever/master cylinder assembly with one from a Yamaha that had dual discs. I have no idea of the bore and stroke of the Yamaha assembly but the result felt the same as factory so it must have been fairly close. Then I got the rotors drilled and I was very happy with the performance and aesthetics.

 

[Bmacleod]

Has the master cylinder been sitting for any length of time with no fluid in it? The seal(s) can dry and shrink without fluid, causing symptoms similar to yours. If you can be sure there is no air, the only other thing I would suggest is using vise-grips to clamp off different lines to take different circuits out of the system to see if the lever comes back. Sometimes a caliper can be defective and cutting off the flow/pressure will isolate it and show you where the problem lies. I would start by clamping the line right below the M/C. If the lever still "sinks", the problem is in the M/C. If the lever comes back, the issue is in the calipers. I hesitate to recommend this as it can be hard on the lines if they are old, Although some would say that if they are that fragile, they should be replaced anyhow. I have used this method a handful of times and it works well.

I am wondering as well about the M/C not being able to operate all those pistons, as mentioned above. Using the vice grips to clamp off the lines to just the center pistons might shed some light on that theory

 

[Larry Fine]

Sidebar:

This is the problem I had when I converted my 750-4 to dual disk.

I looked at doing that back when I had a '73 Honda 750, and I remember thinking that the second fork tube had the necessary holes, that factory parts would work for the caliper except one part I don't remember, and a second disc wouldn't fit the hub without some work. Would you mind sharing the details, if you remember?

 

[Andrew Shadow]

If you are certain that there is no air in the system than I see two possibilities. Either the ratios between the master cylinder and caliper pistons has been screwed up or the master cylinder is defective. The symptom you describe is consistent with a master cylinder that is defective and is incapable of holding pressure due to either seal or bore damage or both.

 

[Roger]

Maybe the (old) hydraulic hoses are swelling a little...?

 

[Uncle Phil]

Already swapped master cylinders and got the same 'effect'. The master cylinder is 'pumping' because I am getting fluid out of the bleeders when I do pump and the pistons are closing on the discs where you cannot move the wheel. I will continue to pump a while and if that does not work, then I'll block off the 'extra' pistons (easy enough to do) and see what happens. My hunch is there is still some air in the system 'hanging out' somewhere and I just haven't got it out yet.

 

[ST Gui]

I looked at doing that back when I had a '73 Honda 750, and I remember thinking that the second fork tube had the necessary holes, that factory parts would work for the caliper except one part I don't remember, and a second disc wouldn't fit the hub without some work. Would you mind sharing the details, if you remember?

LOL it's funny that you included that qualification because it is pretty hazy! I believe the speedo drive had to be modified and there was some machining of the pivot bolt because the second disc didn't line up perfectly. I also flipped the fork lowers around so the calipers were behind the fork legs. I only did the manual labor. A machinist acquaintance did all the tough stuff as he had a later 750-4 (metallic orange with a factory 4>1 IIRC) and was considering the same. He also machined a banjo bolt to connect the two calipers to the master cylinder.

I don't think anything was done to the second leg or disc (other than drilling them both out to look trick). I think it was just the speedo drive and the alignment of the caliper that was the problem. When all was said and done it was an absolute work of art and looked 100% factory. The braking was much improved and it drove a lot of business to the shop.

 

[ST1100Y]

Buy the cheapest possible since they all do the same thing.

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Tend to disagree... tried the one shown in your link and it sucks... not...
Got me a pro model, now that one really draws some liquid (hope that link works over there)
KS Tools brake bleeder

 

[Uncle Phil]

Master cylinder is 'ABSII' which is designed to 'fire' 4 front pistons and 1 rear piston, if I understand how the linked portion worked. From studying the diagrams and the 'plumbing', the line ran from the front to the back to fire the 'secondary' rear piston. With that much length of line, I would not think the new shorter lines to the front 'secondary' pistons would hold much more fluid than the single line. Can't work on it tonight, but I will keep fussing with it until I find a solution. Just for grins, I hooked the output hose of the 'Pro Motion' speed bleeder to the hand cranked vacuum bleeder and it sucked stuff through just fine.

 

[dwalby]

Master cylinder is 'ABSII' which is designed to 'fire' 4 front pistons and 1 rear piston, if I understand how the linked portion worked. From studying the diagrams and the 'plumbing', the line ran from the front to the back to fire the 'secondary' rear piston. With that much length of line, I would not think the new shorter lines to the front 'secondary' pistons would hold much more fluid than the single line.

when we're asking about hydraulic ratio the volume of fluid in the lines is irrelevant. Its the area of the pistons that's important. I lost track of what you have plugged off and what you have active, but if you have more piston area than the MC was originally designed for, you're going to need more lever travel to move the pistons the same distance. If you have 6 active pistons now instead of 4 or 5 on the original design, then that could explain why your lever travel is excessive.

 

[ST Gui]

If you have 6 active pistons now instead of 4 or 5 on the original design, then that could explain why your lever travel is excessive.

+1 And if the diameter of one master cylinder assembly is close to that of the previous master cylinder assembly there will be zero net difference. 'Close' will be relative of course.

In my dual disk mod I went to a master cylinder designed to move more pistons than the factory unit. I didn't do any research as to the size or number of pistons the new unit dealt with in its factory fitment vs my Honda calipers. I lucked out in that designed for double the discs meant the new unit had more than enough surface area for my use.

Will the bike still roll with the brake lever pulled to the grip?

 

[Uncle Phil]

John - Thanks for taking the time to research and 'explanafying'.
So how is the linked rear piston fired when you grab the front lever?
IIRC, there is a line from the front to the back on the linked models so there's some fluid going back there.
I can always swap back to the 'standard' master cylinder just for grins.
I still believe I have some more 'bleeding' to do before I start swapping things.
When I get the 'bleed' to where I am sure there is no air, I will block the secondary line off to see if that makes a difference.
That would put it back like the 'original' design.
If that proves to be effective, then I would swap the master cylinders and see how that works.

 

[kiltman]

I'm finally understanding the operation of the linked brakes. This diagram in the Clymers gives the path. The torque reaction route is the key from the left front caliper that activates the piston in the rear caliper via the SMC, the PCV and Rear modulator. (if only I looked at the diagrams more carefully. Thanks John)

 

[Uncle Phil]

It's amazing what a difference there is when you finally figure out you have a bad bleeder nipple.
I've got 'lever' now - within a 1/4 of an inch of the distance to the grip that I have on the other ABSII bikes.
It will not pull back all the way to the grip as it did before.
I can still pump the lever up some, so I know there is still some air in the system 'hiding'.
Back to the 'beating and banging' to try to dislodge the bubbles!
My hunch is at the end of the day when I get the air out, the pull on the lever is only going to be 1/8"-1/4" closer in than the 'normal' ABSII lever - which is no big deal to me.
BTW, this is using the ABSII master cylinder.

 

[Larry Fine]

It's amazing what a difference there is when you finally figure out you have a bad bleeder nipple.
I've got 'lever' now - within a 1/4 of an inch of the distance to the grip that I have on the other ABSII bikes.
It will not pull back all the way to the grip as it did before.

Yay!

 

[dwalby]

how does a bleeder nipple go bad???

 

[Uncle Phil]

I don't know 'how' a bleeder nipple goes 'bad', but what I do know is as soon as I replaced that one, I could pump the lever up. I finally realized that there could not be that much air in that part of the caliper so I figured I'd replace that nipple and see if it made a difference. I didn't spend a lot of time analyzing the 'how' and 'why' as I did rejoicing that I finally had some appreciable lever pressure!

 

[Andrew Shadow]

I don't know 'how' a bleeder nipple goes 'bad', ......

They are designed to deform ever so slightly when they are tightened so that they conform to and make a seal with the caliper. Similar in principle to the crush washers on the banjo bolts/hose connections. Normally they are good for the life of the vehicle if they have not been excessively over tightened. A leaking bleeder nipple usually is the result of it having been over tightened at some point causing it to deform to much to the point where it can no longer seal.

 

[Uncle Phil]

They are designed to deform ever so slightly when they are tightened so that they conform to and make a seal with the caliper. Similar in principle to the crush washers on the banjo bolts/hose connections. Normally they are good for the life of the vehicle if they have not been excessively over tightened. A leaking bleeder nipple usually is the result of it having been over tightened at some point causing it to deform to much to the point where it can no longer seal.

That appears to be the case with this one - it just was not sealing and letting air get in even when I thought it was closed.