My Linked Brakes

[Chris09]

Does this seem right? A mix of what I've found available through the site and my own beliefs.

Another Linked Braking System Interpretation

Incomplete

The following represents another attempt to understand, assemble, describe and explain the workings of the ST Linked Braking System

When the brake pedal is depressed, brake fluid pressure from the rear master cylinder is applied to two elements; the rear brake caliper center piston and the inlet of the two stage delay valve.

The full brake fluid pressure potential of the rear master cylinder is applied to the rear caliper.

The delay valve which receives fluid from the rear master cylinder has two outlet ports. The first port connects to a tee which branches out to two elements; the front left caliper center piston and the secondary master cylinder inlet. The second port connects to the front right caliper center piston.

The delay valve allows fluid pressure from the rear master cylinder to transfer through a restrictor to the front left-caliper piston and the SMC inlet while initially preventing fluid pressure from acting on the front right caliper center piston until the fluid pressure reaches a specifically determined value.

The effect of rear brake application to this point would be immediate application of the rear center piston and gradual application of the front left center piston [via the restrictor]. In other words, a partial depression and holding of the brake pedal would affect immediate moderate force on the rear caliper, and a gradually increasing force on the front left caliper as fluid crosses the restrictor. Further, if the rear pedal position and pressure is maintained the movement of fluid through the restrictor will proportionately deplete fluid from the circuit causing the rear centre piston to retract.

When the brake pedal is initially applied, fluid pressure moves the spool against the spool valve [compressing the spool secondary spring], this action seals the delay valve secondary chamber, preventing any fluid from passing to the right front brake caliper. At this time all fluid pressure passes through a flow restrictor to the left-front brake caliper.

As the application of the brake pedal is increased, fluid pressure will move the spool and the spool valve as it overcomes the spool primary spring, allowing fluid to pass to the right-hand brake caliper. At this time all fluid pressure is equalized to all three brake calipers.

 

[W0QNX]

Yes or maybe but I can’t really follow that far in my head. But it sounds correct from past reading.

Now explain what happens in the magic loop pictured here.

 

[sirbike]

I’ll take a guess without investigation.
This is on a non ABS bike.

 

[sirbike]

Oh, what happens is the question.
Fluid is conducted under pressure between a master and slave cylinders when the brake is activated.

 

[Al Gully]

Couple pictorials while walking through Chris’s analogy.

 

[Chris09]

I should have said that mine is ABS and I'm ignoring it for purposes of trying to simplify the [at least to me] unsimplifiable.
Also I see more than a few errors in one paragraph [repeated below] which I'm going to correct, whole purpose of this exericise is to see where I'm wrong.

...Further, if the rear pedal position and pressure is maintained the movement of fluid through the restrictor will proportionately deplete fluid from the circuit causing the rear centre piston to retract.

 

[Catmandu2]

Couple pictorials while walking through Chris’s analogy.

quick question,, @Al Gully ,,, is (Deluxe type only) means (ABS only) ?? thx, CAt'

 

[Al Gully]

quick question,, @Al Gully ,,, is (Deluxe type only) means (ABS only) ?? thx, CAt'

You are correct Cat, ABS only

 

[sirbike]

ABS, interesting. That block still might be a shared component between abs and non with the loop accommodating a plumbing difference.

 

[jfheath]

Answering the question - 'Does this seem right?'
(I have edited this following a later exchange - but left the original (wrong) information crossed out so that the discussion later still makes sense. Corrections are added in blue.

No. Bits of it are incorrect - I think you have got your left and right confused in some places.
But I have commented on other bits too

When the brake pedal is depressed, brake fluid pressure from the rear master cylinder is applied to two elements; the rear brake caliper center piston and the inlet of the two stage delay valve.

Yes.

The full brake fluid pressure potential of the rear master cylinder is applied to the rear caliper.

Yes - to the centre piston.

The outer pistons - yes when the bike is not moving. If it is moving, the action of the SMC on the front left caliper bracket tends to operate the two rear outer pistons first. Although it would be difficult to prove that. It is more convenient to think of it this way as the SMC is also operated when the rear pedal applies pressure to the front left brake caliper. So the two rear outer pistons are operated whichever brake lever/pedal is applied when the bike is moving. When stationary, the pedal will apply all 3 pistons - the centre piston directly, The outer pistons by fluid passing by the primary seal in the SMC.

The delay valve which receives fluid from the rear master cylinder has two outlet ports. The first port connects to a tee which branches out to two elements; the front left caliper center piston and the secondary master cylinder inlet. The second port connects to the front right caliper center piston.

I think that it has one inlet and one outlet port. There is a rectangular block before the delay valve which splits the line from the rear master cylinder. One outlet goes across the mudguard to the front left centre piston, the other feeds into the delay valve inlet port.

Yes it has one inlet and two outlets - one to the left centre piston, one tot he right. left outlet is at the top of the delay valve and is conencted by a metal brake line which goes across the top of the mudguard. Fluid id free to flow out of that port irrespective of what is happening with the spools and the brake pedal.

The delay valve allows fluid pressure from the rear master cylinder to transfer through a restrictor to the front left-caliper piston and the SMC inlet while initially preventing fluid pressure from acting on the front right caliper center piston until the fluid pressure reaches a specifically determined value.

As above, the line to the front left centre piston does not pass through the delay valve.

Yes - it restricts pressure from applying the front right centre piston until the pressure at the pedal increases enough to overcome the spring in the delay valve.

The effect of rear brake application to this point would be immediate application of the rear center piston and gradual application of the front left center piston [via the restrictor].

Not quite.
The brake pedal immediately applies pressure to the rear centre piston.
It also applies pressure to the front left centre piston. No delay here. This line also feeds the SMC inlet as you described.

In other words, a partial depression and holding of the brake pedal would affect immediate moderate force on the rear caliper, and a gradually increasing force on the front left caliper as fluid crosses the restrictor.

No - as far as we can work out, the force on the left centre piston is immediate. David labels a restrictor, but adds question marks. His diagram shows the pressure in various parts of the fluid channels and the pressure shown going through the left outlet port is always the same as the pressure shown at the inlet port. He has used cyan, light blue, dark blue for this.

The force on the right centre piston is subject to the delay valve. Initially it closes off the right outlet port, but then additional pressure is Hence the pressure from the pedal is enough to overcome the spool spring and fluid can apply force to the front right centre piston. This can sometimes feel like a sudden dip in the brake pedal, depending on when the right centre piston was last moved. The application is not gradual, but it is never going to be applied harder than the other centre pistons.

Further, if the rear pedal position and pressure is maintained the movement of fluid through the restrictor will proportionately deplete fluid from the circuit causing the rear centre piston to retract.

Hmm. Not really. Pressure from the pedal is increasing. As the delay valve opens, the immediate effect is to want to move the front right piston, and the pedal may be felt to dip, but the same force is still being applied to the pedal and that pedal still applying more force than was there before in order to overcome the spring. And the spring is still pushing back with the same force. If this resulted in loss of pressure in the lines, then the delay valve would close immediately.

When the brake pedal is initially applied, fluid pressure moves the spool against the spool valve [compressing the spool secondary spring], this action seals the delay valve secondary chamber, preventing any fluid from passing to the right front brake caliper. At this time all fluid pressure passes through a flow restrictor to the left-front brake caliper.

Yes. Except the fluid to the left caliper doesn't pass through the delay valve restrictor.

The delay valve is normally open - this is to allow fluid to pass easily through the valve when the brakes are being bled. The instant that any pressure is applied, the delay valve closes the inlet port to the delay valve. You have obviously been looking at those excellent diagrams from @AnnasDad

As the application of the brake pedal is increased, fluid pressure will move the spool and the spool valve as it overcomes the spool primary spring, allowing fluid to pass to the right-hand brake caliper. At this time all fluid pressure is equalized to all three brake calipers.

Yes. The fluid pressure is equalised - the brake pressure is equalised only if all of the pistons are the same size ! (The two front centre pistons are the same size - The two outer pistons on the right are different from the two outer pistons on the left.)

 

[Chris09]

I'm sure I probably have a couple mix ups between left and right, will review and clean that up as well.
Yes, I believe I was looking at the @AnnasDad diagrams which I saved a while back, and I think they are consistent with those in post #5 [taken from the 03 manual maybe?]. All of which I got on this site. In one drawing labeled as model year 06, there's a cross section of the delay valve depicting two outlets, one is noted "Outlet to SMC & Left Front Brake Caliper" and there's a green restrictor drawn in that outlet port noted "Flow Restrictor ???" and the other is noted as "Outlet to Right Front Brake Caliper" So I'm assuming there's a restrictor.
The statement - the full brake fluid pressure potential of the rear master cylinder is applied to the rear caliper - is an excerpt from the Rear Master Cylinder Circuit explanation, not my words. My initial sense from seeing that statement is, they're making some distinction between the affect on the rear center piston compared to that on the front left center piston.
If what you say is true [and I'm sure it is] then the diagrams are incorrect; they depict a three port delay valve and no intermediate component upstream, and if there's no restrictor then rear center and front left center pistons will always be applied at the same rate.
Maybe it's drawn that way for a reason, either way in the absence of a restrictor, the aforementioned statement should be - the full brake fluid pressure potential of the rear master cylinder is applied to the rear caliper and the front left caliper.
The overall affect on the rear outer pistons is demonstrated quite clearly by STRider's videotape where he performs moderate isolated braking in the 50 to 55 mph range. Isolated front brake application results in about twice the SMC plunger travel as what occurs under isolated rear braking. [or so I think I recall correctly].
So if it is the case that there is no restrictor, isolated brake pedal force would provide equal fluid pressure to the front left center and the rear center pistons and rear caliper braking force would increase proportionately based on the amount of SMC plunger travel [I guess].

 

[jfheath]

I'll check out AnnasDads diagram of the delay valve - maybe there was a later revision to the components. Or maybe I am wrong.

There is a proportional control valve in the line from the SMC to the rear outer pistons. This is a 'safety valve'. It is held closed by a strong spring. When the pressure from the SMC increases to a predetermined level, that pressure is able to move a sealed spool against the spring, preventing an increase of pressure at the rear brake outer pistons.

It is possible that the brake pedal operating the smaller front left centre piston is normally insufficient to cause the SMC to apply enough pressure to operate the PCV safety valve. I don't know.

The front brake lever operates the two outer pistons, which have more chance of causing the SMC applying too much pressure to the rear outer pistons, so the PCV safety valve is operated. The additional movement of the SMC shown in the video when the front brake is applied is likely the result of the spool in the PCV valve being moved.

 

[jfheath]

Yes - quite right. Sorry. The Delay Valve has three ports as you say - I was confusing the rectangular block which connects one of the lines going across the mudguard - in fact that particular line is the one from the outlet port of the SMC on its way to the proportional control valve. The other solid tube across the mudguard IS connected tothe top port of the delay valve, and transfers pressure immediately to the front left hand centre piston.

Last time I chatted with David about this, neither of us could think what the 'restriction' port was for. After all - it isn't volume of fluid that is being passed through it. It is pressure. And if a tiny compensation port is all that is required to instantly relieve the pressure in the brake system, then that little restriction port isn't going to stop pressure reaching the front left centre.

I'm wondering if it is a flow control to help with bleeding. There is a device in the SMC - a non-return valve stopping fluid going back through the inlet port. Yet it is free to go through the compensation port. That is the only explanation for that device that I have come up with.

I have corrected my previous reply - crossed out my incorrect statements and extra text is in blue italics.

 

[Chris09]

I see restrictors used in pneumatic controls, [well, not so much anymore] and boiler interock and safety controls for a variety of purposes, but air is a compressible fluid. One possible effect that comes to mind in this hydraulic circuit is dampening [or damping not sure correct term]. I have used restrictors in combination with check valves to affect a delay in pneumatic final control element actuation and fast de-actuation [was a fairly common practice with steam control circuits].
Had a harder look on another thread at ____ 's [will come to me] nothing short of magnificent work on "new toy" Starting taking that interactive model on a spin as well, can't say enough about that contribution to the understanding linked brakes.
I also have quite a bit more description in the larger - Another Linked ... - which I was going to bring into the thread later, as I find it a challenging task to understand some of these control processes in [to what extend they can be considered, if at all] isolation. That larger description draws in all the additional components and dynamics and questions which you've described as well.
Thank you for your time jf in looking at my fairly amateur attempt here, eventually I hope to have two documents; one on the entirely hydraulic ST [ignoring of course the ABS] and another on the [entirely hydraulic] Blackbird. I think these might be two brilliant near-last examples of - untouched by microprocessor - hydraulic control systems, as evidenced by the staggering collective milage this motorcycle has achieved.
I thought I'd start by throwing the middle part out first as I think this is the sweet spot, the moderate range where maybe ninety percent [right, like I did a calculation] of usage occurs. I still think there's a bit more going on here, but then again, I thought there was a second shooter as well. Thanks again.

 

[Chris09]

I photographed my own Majic Loop [will use that] when I had my fairings off. At the moment I haven't got a clue what it's for or where in the system it is but will be reviewing service manual and parts supplier exploded views later on. Maybe it's a dealer service connection or just bracing.
Back to whether or not there's any sort of restriction upstream [standpoint of rising hydraulic pressure] of the left center piston, if there is, it could be there to provide an initial delay, or more graduated application of the front caliper application, the purpose for which might be to facilitate rear-brake-only intended application during slow speed maneuvers or damping dive in abrupt applications.

 

[mjc506]

Good photo - that's not actually a loop in an ABS bike The top line comes from the front m/c, into that top 'clamp' (just a fancy host mount), along the top steel line and into the front 'inboard' ABS connection. Then out from the front 'outboard' ABS line, through the lower steel line and clamp, then back into flexi where it drops down under the triples down to both front calipers (and activates the outer pistons)

The two steel lines further up, that loop around the headstock (no clamps/mounts this side) go to/from the rear. The upper one comes up from the SMC in flexi on the left hand side of the bike, connects to the top steel line on the other side of the headstock, loops around and then into the bottom port of the PCV. The outlet from the PCV then loops back underneath itself and heads to the rear outer pistons via another couple of steel and flexi lines (and the ABS module). The second outlet from the rear m/c goes into steel lines, runs forward, and then just under the PCV and then into the rear 'inboard' ABS module port. The rear 'outboard' port then goes into the lower steel line looping around the headstock, and down to the delay valve, two centre pistons and SMC as described above.

 

[Chris09]

Last time I chatted with David about this, neither of us could think what the 'restriction' port was for. After all - it isn't volume of fluid that is being passed through it. It is pressure. And if a tiny compensation port is all that is required to instantly relieve the pressure in the brake system, then that little restriction port isn't going to stop pressure reaching the front left centre.

Just reading through [again] your brake bleeding articles and sequences of operation and well written explanations by yourself and other members over the years.

Still wondering though, do you know if it has been verified whether or not there is an actual restriction in the Delay Valve port to the SMC and front left caliper piston.
The one image of the delay valve depicts a bright green colored restrictor labelled Flow Restrictor followed immediately by three question marks.
I assume the question marks imply the purpose of it was unclear, but it could also mean that it is uncertain whether or not it's there.
The preceeding paragraph to that image seems to me any way, imply that it does exist, in which case I think its purpose would be to momentarily dampen the rate of pressure rise to the left center piston and SMC inlet compared to [unimpeded flow] the rear center piston.

 

[jfheath]

No

It was ages ago that David and I exchanged emails about this (David = Anna'sDad), and he was last seen on the forums last September. I found a private email exchange from Oct 5 2021, when he spotted that his links no longer worked, and had corrected them.

He got in touch, and gave me a single link to all of his documents and gave me permission to share them with anyone that expressed an interest. I got the impression that he was stepping back a bit.

From our chats, he knew that the 'restrictor' was there, but couldn't work out its purpose. He clearly assumed it was deliberately restricting flow I certainly don't read into it what you have. He doesn't mention the left caliper in his text. Just the potential imbalance front-rear. (I'm not clear why that would be an issue. The front brakes harder than the rear and the rear brakes harder than the front on 'normal' non-linked bikes.)



I think the 'greater stopping power of the two front brakes' refers to the fact that there would be two pistons, one on each brake disc, so that, unrestricted, would exert more power than the single one at the rear. All three centre pistons are 22mm diameter - so the same pressure would be applied equally to all three - except for the front right which is delayed until the brake pedal is pressed much harder.

The 'imbalance' front and rear would not apply as soon as the left front was applied, as it would also apply the rear outers via the SMC, meaning that the rear brake was always applying more braking force then the front - until the right front kicked in.

Except maybe - until the left caliper was moved, the SMC would not be operated. The front left has got to bite in order to apply the rear outers. So perhaps the delay is to ensure that the rear bites first.

It would also ensure that the fluid from the pedal doesn't reach the rear outer pistons before the SMC is operated. (Which is does for example when pressing it in your garage.

But I am intrigued by the shape of that green 'restrictor' . He would not have drawn it as a triangular shape like that unless he had seen it like that. If you wanted restriction, it would be just a small hole.

I think it may be to do with reverse flow. Fluid pressure from the top side would press on the sloping side of the triangle.
Assuming (big assumption) that it is a 'rubber' insert - I think that would flex and close the hole. Which is why I wonder if it is to aid bleeding of the system. That behaviour might explain why it is so difficult to push in the rear outer pistons by hand.


I really don't know. I'm just trying to find explanations, and I am not convinced by any of them. The revers flow to aid bleeding is my favourite - especially since this device exists in the SMC inlet port downstream - also seemingly to prevent reverse flow.



Ages back I created an animation of the delay valve that you might enjoy. I'm not quite happy with it, and haven't published it yet (I don't think).

 

[W0QNX]

No

It was ages ago that David and I exchanged emails about this (David = Anna'sDad), and he was last seen on the forums last September. I found a private email exchange from Oct 5 2021, when he spotted that his links no longer worked, and had corrected them.

He got in touch, and gave me a single link to all of his documents and gave me permission to share them with anyone that expressed an interest. I got the impression that he was stepping back, handing over the reigns with his diagrams.

"He got in touch, and gave me a single link to all of his documents and gave me permission to share them with anyone that expressed an interest. "

I've tried a few times to find all his amazing work on the ST1300. But the links I've followed never show ALL the work only single pieces on google drive.

It would be great if you had a link to everything to share either here or via a personal message.

David and your own thoughts and drawings on the ST1300 design are priceless treasures and I save them to files locally usually.

 

[Chris09]

Good animation.