My Linked Brakes

[Chris09]

So I've gone back to the brake hydraulic schematic and wrote up how I understand the system thus far. I'll ask the questions here and just copy and paste my description below it so as to show what I already [think I] know. In google search for more specifics I came across an instance where someone wound up locking up the rear seems like in a downhill braking circumstance, not all is clear what all the factors were but I wonder if it's possible that the rear can get light enough that strict lever braking can effect enough SMC force to lock up the rear? Wonder if anyone had that experience on a 13. I imagine it would have to be a non-ABS to even know.
I'm mainly interested in specifically how the SMC, Delay Valve and Proportioning Control Valve output pressures rise [and / or hold or drop off] in proportion to rising input pressures. If anything more can be known about these components.

ST 1300 Brakes – Interpreted

There are three master cylinders capable of providing hydraulic force.

• Front MC [Lever Actuated] – The Front MC provides hydraulic force directly and equally to the two outer pistons of the front two calipers. This is the only simple hydraulic circuit and operates in isolation from all the other components. However, while the right caliper is mounted in a conventional manner and remains stationary upon activation, the left caliper will shift CCW and actuate the secondary master cylinder [SMC].
• Brake Pedal MC – The Brake Pedal MC provides hydraulic force directly and equally to the Delay Valve input and the rear caliper inner piston.
• Secondary MC [Front Left Caliper Movement Actuated] – The Secondary MC provides hydraulic force through the the Proportioning Control Valve [PCV] to the two outer caliper pistons.

There are two other fluid controlling components in the hydraulic system.

• Delay Valve – The delay valve receives hydraulic fluid from the Pedal MC and through the first output port, transfers it to the SMC input port. A jumper brake line at the SMC input port transfers unrestricted Pedal MC fluid along to the Left Front Caliper centre piston. As Pedal MC hydraulic pressure increases, the Delay Valve will transfer hydraulic pressure through the second output port to the Right Front Caliper centre piston.
• Proportional Control Valve -

There are three caliper assemblies, each housing three pistons. Each caliper has two separate hydraulic circuits, one for the centre piston, and one for both outer pistons. Caliper operation may occur as either centre piston actuation, simultaneous outer piston actuation, or a combination of both.

• The front right and rear calipers are mounted in a stationary position.
• The front left caliper is mounted in a manor such that as the caliper activates and engages with the rotating disc, the caliper shifts and depresses the plunger of the Secondary Master Cylinder.

Brake Pedal MC – The Brake Pedal MC provides hydraulic force equally to the Delay Valve and the Rear Caliper Inner Piston.

The Delay Valve transfers force from the BPMC in sequence via two outputs; the first connects to the SMC input, then through a hub style connector over to the Front Left Caliper Centre Piston. The second connects to the Right Front Caliper Centre Piston.

The Secondary Master Cylinder transfers force through the Proportioning Control Valve to the Rear Caliper Outer Pistons. The source of SMC output force can originate from either plunger activation caused by left front caliper shift, or from the Delay Valve primary output fluid passing between the SMC plunger lip and cylinder bore.

 

[Igofar]

You went astray at your second bullet :

• Brake Pedal MC – The Brake Pedal MC provides hydraulic force directly and equally to the Delay Valve input and the rear caliper inner piston.

 

[Chris09]

I was going by JFHeath's Going on an Air Hunt - shows two lines out of the Brake Pedal MC, one to the Delay Valve the other to the rear centre piston?

 

[Chris09]

I'm looking at my only service manual I have downloaded, it's for an 03 which shows the same except with the ABS modulators, I guess I should have cleaned that up a bit to indicate location and flow through the modulators, as I have it, it's incorrect and incomplete as a circuit description. Will edit that thanks.

 

[Andrew Shadow]

I'm looking at my only service manual I have downloaded, it's for an 03 which shows the same except with the ABS modulators, I guess I should have cleaned that up a bit to indicate location and flow through the modulators, as I have it, it's incorrect and incomplete as a circuit description. Will edit that thanks.

Have a look at the attached, courtesy of @Anna'sDad.

 

[Chris09]

Have a look at the attached.

Thanks! now I remember seeing this before along with I think a couple others, acurate and much better explanation will do a copy paste for written version reference.

 

[Chris09]

Okay okay, just one more than that's it everyone has to go to bed. So there you are, doing your figure eight in your four parking stalls, you feather that rear brake a bit like you always have done and guess what, the front brake grabs, and where's the centre of gravity now, oh.. there it is. That ever happen to you?

 

[Chris09]

Yeah me neither, geez, who's bike is that, yikes...
Unfortunately, there was a witness, but he couldn't be spared, wrong place at the wrong time, he just knew too much.

 

[Willsmotorcycle]

Yeah me neither, geez, who's bike is that, yikes...
Unfortunately, there was a witness, but he couldn't be spared, wrong place at the wrong time, he just knew too much.

Any chance you have picts on how you mounted those highway pegs?

 

[Chris09]

Any chance you have picts on how you mounted those highway pegs?

They came with the bike when I bought it I'm gonna take a couple of shots later on and post them for you to have a look, they kind of fold out at a 45 and they're a little odd, I've never used them but they're obviously good asphalt spacers!

 

[Sadlsor]

Chris, I dropped my 1300 twice in the first week, doing the tight u-turns.
But it wasn't the LBS that got me, it was just the sheer weight of it all. I came from the KTM 950, a much taller bike to be sure, but also 200lbs lighter.
Having owned several street bikes, sportbikes and dualsports since the 70s, I've only had 2 bikes with the Linked Braking System - this ST1300 and the Honda Blackbird.
I practice lots of low speed drills, including u-turns, Gymkhana, and the Iron Cross. In my view, the LBS is not a limiting factor in these drills.
But you must be comfortable with the weight and with the friction zone.
And with practice, you will increase your confidence level. I'll be honest, it took me some time (and LOTS and LOTS of failed attempts!) before I was really comfortable with leaning this beast in tight circles.
Now it's no big deal -- but I really had to work at it. True confessions.
Think of it this way, too -- police all over the world used this bike successfully for years, and you have seen, I'm sure, some of the drills they must master before becoming motor scouts.
I will assure you, and others here will back me up, that the 1100s and the 1300s are EXTREMELY maneuverable, and highly capable of more agility than many riders are.
Most "mere mortal" riders won't be able to just jump on this bike and start wheeling around in 10-foot 360 degree circles, but with practice and proper techniques, it can be done.
I submit to you that "most" riders don't feel the need to become proficient at such mundane matters, so they won't put in the time and effort to become really good at it.
And that's fine, too.
I simply wish to point out to you, that as usual, "it's the rider, not the bike."

 

[dduelin]

In most every imaginable situation the ST1300's LBS is transparent and does not restrict what you can do with it including tight slow speed precision maneuvers or trailing braking all the way to the apex. If it drops the ground it would have dropped to the ground with or without linked brakes due to technique.

 

[Sadlsor]

Yes.
I wish I had said that.

 

[Chris09]

Yeah good hearing that, no question my skill level is down from not that great in first place, what's the saying, the older I get the better I was, it kind of took the wind out my sails for a bit, I went into that exercise overconfident having achieved some pretty tight turns and low speed control, I thought could this thing be easier than my XL600? Until of course I tried to pick it up. I often ask the question with the kids; do you want to try again or do you want to give up? A little hard consideration for them sometimes but usually a good outcome, but In this instance when I ask myself, the question sucks. I might end up being one in the latter category; I managed to set the bike down without too much of a bump but between the ECU and all the other shock sensitive components I don't know how much of that I want to risk, one thing for sure though I will explore is some less tight pedal braking turns and try to figure out how much front brake application [or grab] might be going on. Thanks again for your perspective much appreciated.

 

[Igofar]

don’t use the brakes, use the friction zone and momentum.
I’m guessing if you fell down, you were looking down, and not where you needed to go.

 

[Sadlsor]

Strong possibility, there @Igofar .
I continually try all the options, and have found what works best for me is momentum as you said, clutch control as you said, and STRONG head turn back to where I want to go. Counterweighting helps me as I get up the nerve to allow leaning with momentum, and a bit less counterweighting when I make the turn quickly.
I know I've said it here before, but it's amazing how counterproductive it can be to look down, even for a split second. (Dammit! Foot dabbed again!)
Heads up, people!
Big head turn with handlebar turn, looking where you want to go. The bike will follow that way.

 

[dduelin]

Not much momentum in slow speed maneuvers but definitely always in the friction zone and steady rpms. High in the friction zone there is very little rear brake needed, feathering the rear pedal is apparently not enough to apply much or any front brake through the LBS.

 

[MidLife]

.......the brake pedal activates with equal hydraulic force the rear centre and left front centre pistons.

Should read pressure, not force. Force is generated by the application of this pressure to whatever area the Honda Engs have designed the pistons to.

The second possibility I see is that instead of a slow rate of progression, the progression occurs at a similar rate until a limit determined at the PCV is reached.

This is it. And once this limit is reached, the PCV shuts off and the outlet pressure to the rear remains constant as you brake harder and the inlet pressure keeps rising

What I don't understand is how the drop in pressure can be achieved while hydraulic supply pressure rises; fluid can't relieve back through the supply line. The only thing I can imagine is that there may be a relief valve and ballast chamber within the rear caliper.

Your imagination serves you well as it is precisely how it works!

Only difference is that it is not happening at the caliper but is all contained within the body of the PCV itself (downstream of its internal shut off valve).

Well... I guess... they work pretty ___ ___ ______ good, ?

Well....do we really know? Has anybody ever tested a PCV on a ST1300? PCV can fail on cars, they are bound to do the same on a ST. It should be possible to test the PCV in place just like it is done on cars

Would be interesting to know what the very high pressure generated by a rear lock-up might do to a PCV. For instance, the Relief Valve you mentioned may be stuck and not doing anything anymore after overpressure. Or some internal seals may have blown, effectively reducing the PCV to what amounts to a useless hard to bleed fitting.

Or maybe it was designed by an Eng. not related to the one who designed the SMC and all is good?

Maybe somebody will run a few tests on some ST PCVs someday and let us know.

 

[Chris09]

Should read pressure, not force. Force is generated by the application of this pressure to whatever area the Honda Engs have designed the pistons to.



This is it. And once this limit is reached, the PCV shuts off and the outlet pressure to the rear remains constant as you brake harder and the inlet pressure keeps rising



Your imagination serves you well as it is precisely how it works!

Only difference is that it is not happening at the caliper but is all contained within the body of the PCV itself (downstream of its internal shut off valve).



Well....do we really know? Has anybody ever tested a PCV on a ST1300? PCV can fail on cars, they are bound to do the same on a ST. It should be possible to test the PCV in place just like it is done on cars

Would be interesting to know what the very high pressure generated by a rear lock-up might do to a PCV. For instance, the Relief Valve you mentioned may be stuck and not doing anything anymore after overpressure. Or some internal seals may have blown, effectively reducing the PCV to what amounts to a useless hard to bleed fitting.

Or maybe it was designed by an Eng. not related to the one who designed the SMC and all is good?

Maybe somebody will run some tests on a few ST PCVs someday and let us know.

Should read pressure, not force. Force is generated by the application of this pressure to whatever area the Honda Engs have designed the pistons to.



This is it. And once this limit is reached, the PCV shuts off and the outlet pressure to the rear remains constant as you brake harder and the inlet pressure keeps rising



Your imagination serves you well as it is precisely how it works!

Only difference is that it is not happening at the caliper but is all contained within the body of the PCV itself (downstream of its internal shut off valve).



Well....do we really know? Has anybody ever tested a PCV on a ST1300? PCV can fail on cars, they are bound to do the same on a ST. It should be possible to test the PCV in place just like it is done on cars

Would be interesting to know what the very high pressure generated by a rear lock-up might do to a PCV. For instance, the Relief Valve you mentioned may be stuck and not doing anything anymore after overpressure. Or some internal seals may have blown, effectively reducing the PCV to what amounts to a useless hard to bleed fitting.

Or maybe it was designed by an Eng. not related to the one who designed the SMC and all is good?

Maybe somebody will run a few tests on some ST PCVs someday and let us know.

Good point, I was assuming for some reason that the all centre and all outer pistons would be the same diameter. I was thinking earlier of doing just a quick and easy test suspending both wheels and seeing if I could get an idea of a start point for each caliper and possibly compare the difference in resistance early in the pedal application. At the same time do the SMC test.
Reviewing the link you've included though I'm thinking more about investing in one of those kits. Thanks!

 

[Chris09]

don’t use the brakes, use the friction zone and momentum.
I’m guessing if you fell down, you were looking down, and not where you needed to go.

Yeah I think that was a contributing factor or you've nailed it outright, after reading some I went for a short trip on the bicycle with the dog leash, I never look at the bicycle. Short trip on the ST without looking at the ST, focusing more on where I want to get to, and I think that might be where I made my previous mistake, short trip on the XL, there again, I never look at the XL.
Another thing I found with the ST early on was that when the windshield was up, I tended to look at it and if affected / distracted my balance at slower speeds.