Linked Brakes

[tbloor]

Morning Everyone,

I've bought a 1999 ST1100 at 150,000km. I don't know if I'm missing something, but when the bike is on the center stand, I roll the rear wheel and squeeze the front brake, but the rear just keeps rolling. I'm assuming this means the linked braking system is no longer working. The rear and front operate separately, and have plenty of bite and the pads are fresh. Is it worth reinstalling this system? I'm presuming that isn't an easy job.

Thanks!!

 

[Mike M.]

None of my st1100's have linked brakes and ABS. I think if your bike does not have ABS then it most likely also does not have linked brakes.

 

[Alberto]

My bike doesn’t have linked brakes, but if I remember correctly, the rear brake is activated by a secondary master cylinder on the front fork, and it only engages under load, when you’re braking while moving.

 

[ST1100Y]

I think if your bike does not have ABS then it most likely also does not have linked brakes.

His avatar clearly shows a post '96 ABS-II/CBS...
But who knows if a PO has either neglected or disabled the CBS circuit...
I'd get a w/shop manual and go though the checking procedures one by one...

 

[tbloor]

Thanks guys, it is indeed a 1999 model with TCS and ABS. The under load part is interesting, I have no idea how to safely engage that! . As I said the braking feels solid, but not sure if this is a known issue with aged bikes.

 

[tbloor]

Interestingly I asked Gemini, and this was the response. If anyone can confirm based on not being an AI, that would be great. “
There’s often some confusion about how the Linked Braking System (LBS) on the ABSII models (post-1996) actually triggers. Here’s the breakdown:


• Fork Compression: The rear brakes do not activate simply because the forks are compressed under load or braking dive. The system is torque-reactive, not suspension-sensitive.


• The Pivot Mechanism: Activation requires the front wheel to be spinning. When you grab the front lever, the left-side caliper "swings" on its pivot due to the friction/torque against the rotor. This mechanical movement is what strokes the secondary master cylinder mounted on the fork leg.


• On the Center Stand: If the bike is stationary, pulling the front brake will not engage the rear. Without the "drag" of a spinning rotor to move that left caliper bracket, the secondary master cylinder stays static.


• Testing/Bleeding: This is why you can't test the linked functionality while parked. To bleed the system properly or test it on the stand, you have to manually unbolt/pivot the left caliper bracket to simulate that rotational torque.


TL;DR: No rotation = no link. Static fork compression does nothing to the rear circuit.”

 

[Uncle Phil]

ABSII (1996 and later) is the only model of those years with linked brakes (the other model is the standard).
The quickest way to know is look at the front fender - the ABSII has a two piece and has fork 'protectors' built into the front fender.
You will also see 'plumbing' across the top of the front fender.
The wheels will have sensor rings front and back but someone could have done a wheel swap.
Also over here, the turn signal indicators are half way down the speedo cover on ABS bikes and up in the light bar for the standards.

 

[tbloor]

Yep that's definitely what I have. I'm going to assume that the linked brake system is operating when both wheels are turning, unless there anyone knows any easy way to test it when static, without pulling it apart! Thank you gents to everyone who has already helped me confirm this.

 

[Ryan_B]

I don't know how the ST1100 is, but the ST1300 you can actually squeeze the secondary master cylinder with your hand and it will engage the rear brakes. You basically lay down next to your bike when it is on the center stand, you can kick the rear wheel with your foot and cycle the secondary master cylinder with your hand (it is mounted on the front left caliper and pivots forward). It only moves like 1/8th an inch, but it will stop the back tire immediately.

Picture borrowed from the internet:


Ryan

 

[Uncle Phil]

Yep, when I clicked on your avatar and got a good look at the front end of your beautiful blue (my favorite color of) ST1100, it is definitely a ABSII. If the ABS is functional, the ABS lights should come on when you turn the key on and then go out after you start rolling. If it has a problem, they will blink and you can retrieve the fault code.

 

[Andrew Shadow]

Rotating the left front caliper upward on its pivot point will cause the activation of the SMC enabling it to be tested when stationary.
I would suggest a good cleaning and lubricating of all of the pivot points and moving parts to ensure that everything is able to move freely. Might as well do the same for the entire brake system if you aren't sure what condition it is in.

From the Honda service manual;

 

[Alberto]

Yep, there are pictures of SMC on my neighbours st1100, it linked to caliper via movable bracket

 

[SMSW]

It only moves like 1/8th an inch, but it will stop the back tire immediately.

It should stop the back tire immediately, if it is functional.

 

[jfheath]

The SMC on the 1100 looks very much like the rear brake master cylinder - the pushrod end is pointing downward so water cannot pool around the boot. It doesn’t have the same issues as the SMC on the ST1300 that some people seem to experience after years of neglect. But the ST1100 has a 3 bolt pivot bracket mechanism hidden behind a plastic shroud. It is easy not to notice that it is slowly rotting away, but It is easy to take apart, clean up and lubricate, once you get the rusted split pin out of the Clevis pin.

I did one last year that was locked up solid. Three pivot points, non of them would move without the use of a vice. Most of the problem was the rust on the two curved plates and the pivot pin for the master cylinder. The clevis pin was rusty and too big for the hole, the split pin was rust welded in the clevis pin. It had to be driven out and given some aggressive cleaning. The hole needed reaming. The two needle roller bearings in the ace-of-clubs casting were locked solid with dried grease, but became free with a bit of Jfheath cleaning technique. Everything else cleaned up nicely. The only thing I had to buy was a new split pin - my old tin full of various sized split pins did not have one the correct size. It does now.

I’ve got nice diagrams of this if you need them. Basically, when you apply the front brakes, the caliper moves with the brake disc and that bracket and casting converts the movement to push the SMC pushrod upwards to apply the rear brakes. It’s important that the mechanism moves and returns freely.

There is a proportional control valve in the brake line after the SMC which limits the otherwise uncontrolled braking force that is applied to the rear brake.

So the brake system layout is the same as the 1300: Rear pedal applies all 3 centre pistons; Front brake lever applies the 2 sets of outer pistons on the front calipers; The SMC operates on the two rear outer pistons. The right fork leg on the abs/cbs version has an anti-dive mechanism. The SMC operates when either the brake pedal or the brake lever is applied because both provide some braking force to the front left brake.

 

[jfheath]

ST1100 SMC for ABS/CBS models

I thought that I knew how to put this thing back together again, having done it a couple of times before. But when I tried last year having not touched an 1100 since 2006 - I needed the diagram to refer to. That didn't help a great deal either - with arrows going all over the place. I eventually got it sorted, but thought that there had to be an easier way.

I don't know whether these diagrams help, but I did most of them at the time and thought that they ought to be on here. Anyway I enjoyed the colouring in !

1. The main components.
Here we have the main components of the SMC assembly.

Light blue - the master cylinder itself

Pink is the 'Arm Set'. I tend to refer to it as the Ace of Clubs Linkage. This has a bushed hole (light blue) and two needle roller bearings with oil seals.

The bush inside the roller bearings protrudes at each end so that when everything is bolted together, the arm is free to move.

The bushed hole in the linkage (shaded light blue on the pink Ace of Clubs Link) is connected to the bracket on the bottom end of the Master Cylinder.
In grey are the two plates - called Plate A and Plate B on the Honda fiches - the one at the back (top in the image) has threaded nuts welded to the back of each hole.

---

2. The SMC link to the Ace of Clubs Linkage.

There is a clevis pin and a split pin. The bracket on the end of the Secondary Master Cylinder (SMC) is secured to the Ace of Clubs link with the clevis pin, and the clevis pin is secured with a split pin through a hole in clevis pin after is is pushed into place.

The head has a thin, flat head. It is circular, has a section that is ground flat. This corresponds to the flange that is kbent over at the bottom of the SMC bracket - visible in the diagram. This stops mthe pin from turning and therefore preventing the split pin at the opposite end from being worn away.

This assembly needs to be quite thin so that the bracket needs to be able to move freely in between the two plates.
The clevis pin needs to be greased - not to aid movement, but to protect it from corrosion. Brake pad grease such as Ceratec, or a smear of Moly 60 - both seem to have the ability to stay put in harsh conditions.

---

3. The assembled components.
Missing from the previous diagrams are two essential components : The fork leg and the caliper bracket.

Both fixing points on the left fork leg have a bush inside a needle roller bearing and this needs to be greased. There are also oil seals.
The left hand side of the curved plates are bolted to each side of this bush. The front plate, the bush and the rear plate are bolted firmly together onto the fork leg. The plates are fitted so that there is a gap between them for the SMC bracket and clevis pin to move without touching,.

They should pivot easily in the bearing although final tightening should be left until later.

The clevis pin is already secured in the bushed hole of the Ace of Clubs link, but I have not shown this in the diagram on the left. it makes it easier to recognise the SMC bracket behind the visible plate.

The other two holes in the Ace of Clubs link both have bearings with a protruding bush. The centre bush in the Ace of Clubs link is clamped between the right hand side of each of the plates.

The bottom end of the (light blue) master cylinder sits between the two Igrey) curved plates. The master cylinder bracket should not touch the plates..

The remaining bearing in the ace of clubs link is fitted between the two arms of the brake caliper bracket. In fact the bolts only function is to clamp the bush to the inner arm of the caliper bracket. The hole in the outer arm of the caliper leaves a tiny gap around the bolt head. A little grease around that outer hole will help prevent corrosion.

---

4. The Workshop Diagram

Below is the colour coded diagram that is in the workshop manual. I haven't rearranged anything in this. I've used the same colours as before to try to highlight the components. The the arrows in the o.riginal - to show where each part of the diagram is connected to another part - are also colour coded.

I have removed the arrows and the torque settings for each bolt from the original Honda diagram - which helps to simplify it somewhat.

The operation of the linkage is quite simple. The caliper bracket is moved up when the brakes are applied due to the rotation of the disk, so the SMC bracket is also pushed up. The odd linkage allows the caliper bracket to move in an arc but the master cylinder push rod is moved straight up.

If any of this mechanism seizes up, then the SMC cannot be activated as it should. But there is plenty of force when braking to make sure that it does. Applying the brakes is not a problem. But allowing them to release afterwards is. If your rear brake is always too hot to touch after a ride then this linkage may be the problem.

The mechanism is largely hidden behind that grey shroud, and it can go years without attracting the attention. Yet done regularly, it is a straight forward job - although removing the grey shroud may be an issue - it is screwed from the inside of the mudguard.




5 A Photo of the item itself

An image that I found on the web of the linkage as a part for sale.

The unattached end of the plate will be rotated anticlockwise and bolted through the fork leg bearing.

The clevis pin will be between the two plates - and the SMC bracket will be attached to that.

The free bearing in the Ace of Clubs link will be attached to the caliper bracket.

---