My Linked Brakes

[Igofar]

Does this help? (Not my pictures)

 

[MidLife]

Does this help? (Not my pictures)

This is great! Thank you. Good to see what it looks like in real life.

On the left: The Shut Off Valve, normally open, so the SMC pressure can propagate straight to the rear, without restriction, under light braking (and system bleeding) conditions.

Brake a bit harder and this valve shuts off (upwards shift on the picture), isolating the rear and trapping the pressure in it to a constant level (plateau).


On the right: The Pressure Relief Spool (Sometimes called "Decompression Piston")

The big spring on top of the "Piston" is what the SMC pressure has to work against. Brake even harder and the SMC pressure climbs to a point where it can overcome the spring force, allowing the "Piston" (spool) to shift against it (upwards in the picture) which "decompresses" the rear brake line, progressively decreasing the pressure and tapering down the rear braking force.

Then, when going back to be softer on the brakes after the emergency grab, the SMC pressure will drop back down, which allows the big spring to push the "Piston" back (down) and progressively "recompress" the rear brake line to the former "plateau" value.

Further release the brakes and the Shut Off will reopen, again allowing straight linear transmission of the SMC pressure to the rear.




Not sure how the shut off works. I suppose there must be a bore and seal inside the shiny top piston with outside o-ring? And the bronze looking part slides inside it? And for it to work, it looks like the seal on the bronze part should be in a groove with a bit of free play up and down, or at least have a soft compressible lip on the bottom side?

From the pics, if I get it correctly, what is remarquable is that there are two dynamic seals holding back the brake fluid pressure directly to outside ambient. A leak from either of them would result in loosing brake pressure to the rear (and ultimately to the two front center once the rear reservoir is depleted). But have never heard of such a failure (except for the early recall on the PCV, although they never specified what was leaking, could have been internal).

Thanks again!

 

[jfheath]

Years back, @Anna'sDad sent me links to a couple of excellent diagrams that he produced of cross sections of the delay valve and of the proportional control valve, and we had many exchanges and discussions about these and the workings of the SMC. He drew them showing different stages of operation with explanations.

I know that he posted them on the forum at some point, but I cannot find them now, snd they are not my property to re-post.

I produced an animation of the operation of the PCV, but it failed to convert to a format that I could post. I will see if I can use screen capture software to show it.

 

[ibike2havefun]

Years back, @Anna'sDad sent me links to a couple of excellent diagrams that he produced of cross sections of the delay valve and of the proportional control valve, and we had many exchanges and discussions about these and the workings of the SMC. He drew them showing different stages of operation with explanations.

I know that he posted them on the forum at some point, but I cannot find them now, and they are not my property to re-post.

I produced an animation of the operation of the PCV, but it failed to convert to a format that I could post. I will see if I can use screen capture software to show it.

There's this diagram, which I think is not the one you're talking about:
SMC Rebuild | ST1300-Brakes | ST-Owners.com

I think I know the one you're referring to- it was a superb illustration. It appears he had it on Google Docs but the link I found no longer works. Perhaps the thread context itself will do the trick for the OP?

 

[Chris09]

Does this help? (Not my pictures)

Thanks!

 

[MidLife]

There's this diagram, which I think is not the one you're talking about:
SMC Rebuild | ST1300-Brakes | ST-Owners.com

I think I know the one you're referring to- it was a superb illustration. It appears he had it on Google Docs but the link I found no longer works. Perhaps the thread context itself will do the trick for the OP?

There is a brake system diagram by Ana's Dad (attached) that is similar to the one you are pointing to and includes a short description of the PCV purpose:



Where, as the SMC pressure rises, the 3 stages are:

1) Valve is open and the pressure can rise up to the set limit
2) Shut-off valve closes and the pressure is held at the set limited pressure
3) Decompression piston is activated and reduces the pressure

 

[Chris09]

I'm just going to throw out a few of my own guesses and see if anyone can say I'm on or off track, complete with not the most appropriate terms. Bear in mind I'm in no way convinced I understand this, it's all just musing at this point.

I'm just gonna call the parts the cap, the casting, the steel, the brass, the piston, narrow spring, large spring, retainer.

Assembled, the inside of the cap would provide some initial compression of the large spring against the steel, seating the tapered surface [ that I'm going to call the valve ] against a machined surface [ that I'll call the seat] within the housing.

The outer disc of the steel which sets against the tapered end of the large spring does not rest directly against the casting; there is a small clearance which enables the minimum spring force to occur between the valve and seat.

Under moderate pedal activation and release, fluid moves forth and back through the "doughnut channel" of the housing in the region along the lower narrow portion of the steel between the lower O Ring and valve.

Under moderate pedal activation and release, this flow way presents no significant restriction.

I know it's contradictory to some of what's been said so far but that looks like a pretty strong spring for a very small valve, whereas the cup on the end of the brass looks more like it would be used to seal the end of an expanding column of brake fluid.

Also it's the chamber closest to the connections.

But my train runs off the tracks [again maybe] at this point, assuming the brass is assembled [and I think it is] as shown, it appears that the small spring goes over the brass [which I think it must or there would be no alignment of the cup]. There doesn't seem to be much if any potential of an expanding / contracting fluid chamber.

I'm gonna guess at least two responses,

"off, off, ... teetering on one rail... nah, off."

"why don't you ask your ______ hamster... smart ass..."

 

[OkieRider]

I just cut those things off my bike and was prepared to throw them in the garbage. If somebody wants to take them to play with and run hydraulic tests to confirm their theories and/or cut them open for educational purposes, I'm fine with that as long as they share their results with the community.

 

[Chris09]

I would definitely like to do that. I would pay for the shipping and return them as well. I'd like to set up a table of applied pressure vs outlet pressure over time and from that do a calculation somehow, [once I determine all the piston diameters and swept area,] of proportion of stopping forces. Then I'd like to rig up a small gauge that can be easily primed and connected to the rear outer piston bleed caliper for a quick and easy check.
It all started when I was seven, I wasn't like the other boys, then when I got older and after I had been through a succession of unsuccessful relationships that ended badly and with me being confused, I found this 1985 XL 600. By that time, I had my cars, I was done with motorcycles, I wouldn't look out the window if E.J. Potter was driving back and forth [unless he was driving the one with the little plug in front of the block, I love my 327].
I was over at a relative's place and I said "hey, you know, I come over here and I see that bike, now you got it under the deck, how long before it winds up in the rain and ends up on the scrap heap, are you ever gonna do anything with it?"
So, I probably shouldn't have said that. So, then it's on the trailer, more ____ I don't need or have time for but It's just two wheels with a lawnmower engine, hey, how hard can it be?
A thread for another time or place but the relevance is I went down the rabbit hole with that one, I had no idea what an engineering marvel the thing really had been. I documented a good deal of my trials and errors in getting it working and figuring it out and I wrote a fair bit on it, [all plagiarism of some sort or other]. The bike is rough, visually almost everything original but...
It's a dual sequentially carbureted hemi radial four valve [actually five] combustion chamber four inch diameter thumper with dual exhaust, it shouldn't even work.
Somewhere, Soichiro was thinking... "hmmm... little red bike... I'll show you little red bike... I got something that's really gonna ____ ____ __".

 

[MidLife]

I'm just going to throw out a few of my own guesses

Had no luck tracking Ana'sDad illustrations. But when jfheath manages to revive some of his schematics, you'll picture it all in a flash, with no guessing involved.

I'm just gonna call the parts the cap, the casting, the steel, the brass, the piston, narrow spring, large spring, retainer.

So let's go with that!

.........seating the tapered surface [ that I'm going to call the valve ] against a machined surface [ that I'll call the seat] within the housing.

You like high-tech, but sorry, there are no metal to metal seals in the PCV. Sealing metal to metal requires high precision machining, high seating forces and "casting" is not the material of choice for it either. And you'd have to throw the PCV away once the sealing surfaces are worn. Only serviceable elastomeric seals in this valve.

So far, it sounds like you are going along with the concept of the three stages of activation?

1) Low and rising SMC pressure: PCV valve is open and pressure freely transmitted through it?

2) SMC pressure reaches Honda's set limit for the rear and the shut off valve closes? For illustration purpose only, let's say this limiting pressure is 300 psi.

3) SMC pressure keeps rising to a point where Honda has decided it is time to taper off some of the rear braking power? Let's go here with this higher pressure maybe being 600 psi.

Then you recognized the Brass spool, working against a small spring, and the Steel spool, working against a stronger spring.

Physics dictates that the spool with the weaker spring will shift first and then the spool with the stronger spring will come in second as the SMC pressure rises (neglecting some other factors).

So in the hypothetical illustrating pressures example, the Brass Valve would shift first against the small spring at 300 psi: Hence the Brass Valve is the Shut Off valve that initiates the second stage (constant limited pressure on rear).

And the Steel Valve would follow at 600 psi: This is the Decompression Piston that initiates the third stage (decreasing rear braking pressure).

If this seems to make sense, I can pursue later with describing how each valve works.

Below to illustrate the location of the components:

 

[jfheath]

Links to @Anna'sDad's excellent drawings showing a cross section and explanations of the workings of the Proportional Control Valve and the Delay Valve.

The Proportional Control Valve

The PCV is responsible for limiting the pressure from the SMC to the outer pistons of the rear caliper, and reducing it when a set pressure threshold is reached.

Link to Anna'sDad's Drawing of the PCV


The Delay Valve

The Delay valve allows pressure from the rear brake pedal to be applied tot he front left centre piston, but delays the operation of the front right centre piston until a set pressure threshold is reached.

Link to Anna'sDad's Drawing of the Delay Valve


Animation

Link to my Animation of the Delay Valve based entirely on Anna'sDad's drawings

 

[OkieRider]

I would definitely like to do that...

PM your address. You can keep them for destructive testing/investigation.

 

[Chris09]

Yeah that would be great, not sure how I should get that to you, not concerned about people on this site but wonder if it's wise to post address on forum.
Appreciate everyone's efforts in trying to elucidate this for me but hey, I can be as thick as two short planks.
I don't think I'll be singing the Rain in Spain until I get one of these things into the Consume - a - tory for critical analysis.

 

[Igofar]

Send a private message (start a message) to each other, no one will see it but you two.

 

[MidLife]

Send a private message (start a message) to each other, no one will see it but you two.

This may help going through two short planks.....---->> Start Conversation

 

[Chris09]

This may help going through two short planks.....---->> Start Conversation

Hey Thanks!

 

[MidLife]

Hey Chris,

A long time ago, I read something along the line of the below on ST-Owners that is a simple approach to help visualize and take advantage of the brakes set -up (I wish I could give credit, but can't find this post either!) :

-- The front lever alone always gives you access to a good 60% of the full braking power available, energizing two out of three pistons all around, with Honda doing the rear modulating for you.

So most of the time, it can all be done with just pulling the front lever and leave the pedal alone.

Need more in a pinch? Pushing on the rear will additionally engage all the center pistons and give you full braking power.

 

[Igofar]

The only thing I would add to Midlife's comments would be to use the pedal at traffic lights, and everytime you stop.
You want to exercise the pistons to keep them from getting dirty, and start sticking on you.
Its the old, "if you don't use it, you loose it"

 

[dduelin]

Hey Chris,

A long time ago, I read something along the line of the below on ST-Owners that is a simple approach to help visualize and take advantage of the brakes set -up (I wish I could give credit, but can't find this post either!) :

-- The front lever alone always gives you access to a good 60% of the full braking power available, energizing two out of three pistons all around, with Honda doing the rear modulating for you.

So most of the time, it can all be done with just pulling the front lever and leave the pedal alone.

Need more in a pinch? Pushing on the rear will additionally engage all the center pistons and give you full braking power.

Muscle memory does not respond very well in a pinch. Rider training with most every reputable course teaches the use of both brakes every stop. When the chips are down and all available braking power is needed it's best to "do it without thinking."

 

[Chris09]

Thanks for everyone's input, I've never taken any rider training, can't remember if I told the story already, first speeding ticket on motorcycle back in 1985 went ...uh, I don't have a motorcycle license... the officer answered, yeah well, neither does anybody else so don't worry about it, - gave me the smallest fine and let me push it into a parking lot where he knew I'd come get it an hour after he left.
So after that I promptly failed the pilons, went to the pilon course at night a few times, got through it and took my road test. Probably should take a course.