Rear brake binding

[ST1]

I have a UK registered 2008 ST 1300 A6 28000 miles.
There is a problem with the rear brake, when I use the brake pedal the rear brake does not fully release.
Less than a quarter of a turn is possible if I try and spin the rear wheel.

So far I have replaced the SMC, and lubricated the lower pivot point.
Rear caliper.
Replaced x 3 pistons and seals
Metal retainer clip to caliper bracket.
Caliper pad spring.
Genuine Honda brake pads.
Pad pin.
I have followed the JFHeath guide to bleeding the brakes.
Using a mighty vac.
After all this the first press on the pedal and the rear brake binds.

I am at a loss what to do next.

 

[OldMcClelland]

SMC problem.

 

[Igofar]

Take a couple pictures of the following:
The rear caliper mounting bracket (through the rear tire from the right side) so we can see the forward foot of the brake pad, and how it is seated in the silver clip.
We also need to see the rear caliper mounting bracket/silver clip area up close.
If possible, remove the rear caliper, and take a picture of the HOLE that the stopper plug goes into.
If you see spiral flutes (sand waves) your bracket is damaged.
If the front silver clip is loose, your bracket is damaged.
If the clip is easily removed (falls out)...yup, your bracket is damaged.
On the front left caliper (SMC) while the pivot bearings (lower mounting point) need to be greased, there is alot more to be inspected and checked.
Have you, or anyone else opened up the SMC? if so, you should probably replace it, as it is pre-measured from the factory for the correct depth that the plunger sits/moves.
If you have your body work off the bike, place a hose on the PCV bleeder, crack it open, then while its open, go to the SMC, and press the plunger into the bore as far as you can.
If the piston is not frozen/rusted in the bore, you should be able to move the piston almost 1/2 of an inch (smoothly) If it don't move, your SMC must be replaced.
Stop using a mighty vac, and get a simple one way check valve (motion pro) it will work much better.
reach out and send me a PM if you need further assistance.
Igofar

 

[ST1]

silverclip


Original parts which have been replaced.

 

[draser]

So far I have replaced the SMC lubricated pivot point.

So.. you replaced the SMC and lubricated the pivot point, do I read this correctly?

Replaced x 3 pistons and seals

Did pistons go in easily by hand at reassembly? Did you lubricate the seals and outside pistons as per manual?

Your rear caliper bracket shows wear, there's a gap (showing in your pic) between bracket and pad retainer clip that sits in the bracket recess and there's way too much grease everywhere in there. I'd remove caliper, clean all the grease away and inspect the stainless pad retainer clip and its recess in the caliper bracket, if the clip is loose in the bracket I'd get a new bracket.

1 - caliper sliding pins - there's a skinny pin part of the caliper bracket and a thicker one that screws into caliper but the sliding portion sticks in a recess in the bracket. If there's too much grease in that recess or on the pin that will prevent caliper from freely "floating" sideways and cause brake drag. For the thick pin and its recess, I'd clean all grease off then smear some moly grease on the pin only and ensure it slides freely in the caliper bracket recess. Look at the pin (when clean) for shiny wear sections, if it can be felt by fingernail I'd replace.

2 - pad hanger pin (the long skinny pin that hold pads and has a plastic cap) - ensure there are no ridges felt with fingernail that will prevent pads from freely sliding on the pin. I smear a very light coat on moly on it as well, better yet some moly dry lube spray.

3 - pad greasing - just smear some moly grease on the pad "legs sides" that go into the pad retainer clip.

4 - pads anti-rattle spring - installs inside the caliper body, if you had it out for cleaning ensure that the clip was placed back in there with correct orientation, see manual exploded view.



5 - upon caliper and bracket reassembly onto the rotor, with the pistons fully retracted ensure caliper body moves freely sideways.

6 - upon system bleeding and when brakes are operational, ensure that, after front/rear brake application - bike on centerstand - you can minutely move the rear caliper up/down on the rotor - which indicates caliper is not stuck due to residual pressure or mechanical misassembly.

 

[ST1]

Take a couple pictures of the following:
The rear caliper mounting bracket (through the rear tire from the right side) so we can see the forward foot of the brake pad, and how it is seated in the silver clip.
We also need to see the rear caliper mounting bracket/silver clip area up close.
If possible, remove the rear caliper, and take a picture of the HOLE that the stopper plug goes into.
If you see spiral flutes (sand waves) your bracket is damaged.
If the front silver clip is loose, your bracket is damaged.
If the clip is easily removed (falls out)...yup, your bracket is damaged.
On the front left caliper (SMC) while the pivot bearings (lower mounting point) need to be greased, there is alot more to be inspected and checked.
Have you, or anyone else opened up the SMC? if so, you should probably replace it, as it is pre-measured from the factory for the correct depth that the plunger sits/moves.
If you have your body work off the bike, place a hose on the PCV bleeder, crack it open, then while its open, go to the SMC, and press the plunger into the bore as far as you can.
If the piston is not frozen/rusted in the bore, you should be able to move the piston almost 1/2 of an inch (smoothly) If it don't move, your SMC must be replaced.
Stop using a mighty vac, and get a simple one way check valve (motion pro) it will work much better.
reach out and send me a PM if you need further assistance.
Igofar

So.. you replaced the SMC and lubricated the pivot point, do I read this correctly?

Yes

 

[draser]

That's what I thought. I just sent some rear caliper inspection/install detail, you may have already done most of it, it's intended for a check list type review.

In summary, the rear caliper dragging may be caused by: a) front left caliper drag; b) SMC not releasing rear caliper pressure after front braking; c) rear caliper issues (wear/maintenance, misinstallation); d) rear brake MC not releasing pressure after rear braking; . Based on what you're seeing on your bike you can then focus on a specific area.

The rear wheel spinning test - it's pretty subjective, especially if you replaced rear bearings the number of turns is questionable. A more accurate test is temperature of the rotors, if the bike is rideable of course.

 

[MidLife]

That's what I thought. I just sent some rear caliper inspection/install detail, you may have already done most of it, it's intended for a check list type review.

In summary, the rear caliper dragging may be caused by: a) front left caliper drag; b) SMC not releasing rear caliper pressure after front braking; c) rear caliper issues (wear/maintenance, misinstallation); d) rear brake MC not releasing pressure after rear braking; . Based on what you're seeing on your bike you can then focus on a specific area.

The rear wheel spinning test - it's pretty subjective, especially if you replaced rear bearings the number of turns is questionable. A more accurate test is temperature of the rotors, if the bike is rideable of course.

Small add-on to this nice logical approach.

-- The SMC also engages with rear braking only.
-- Rear pressure can also be trapped by a kinked, pinched or damaged line (and/or overfilled reservoir).

 

[draser]

The SMC also engages with rear braking only

Oh, how's so?

 

[Art Franz]

Oh, how's so?

It’s called a linked braking system. When you depress the rear pedal, 2? pistons in the rear caliper are activated and push on the pads, and 1 or 2 pistons (not positive of this but something like this) in the left front caliper is activated which also activates the smc. When you press only the front brake, the smc is activated which then activates the 3rd piston on the rear caliper. I know, terribly complicated and completely unnecessary IN MY OPINION. A huge source of problems that should have never been put on this bike. Again in my opinion, the weakest and most problematic of all the components and systems on this bike. But when working properly, it is incredibly effective and powerful, and works very well as it was designed.

Caveat: I don’t have all of the technical data re the pistons, number of pistons, and sequences involved in my description above, in my memory. And I didn’t bother to look that up in my shop manual to be sure of the accuracy of my statements above. My point was to give you an idea and approximation of how the linked system in this bike works. I’m sure someone that is much more familiar with the brakes of the st1300 will chime in with the correct data. Just trying to be a wee bit helpful and up my number of posts on this forum at the same time. See, I can multitask after all lol

 

[Al Gully]

All,
Here is a brake simulator that Matt posted.
Brilliant, watch for the colored lines bulging when you use the front/rear slide tool.

Article [13] - ST1300 - Brake System Simulator | ST1300 Articles

A distinct lack of contributions to the forum recently (I blame "other projects"... :well1: ) so here's a dirty "simulation" of the ST13 braking system!! https://mjc-506.github.io/st1300braketoy/ I've tried to get it as accurate as possible, but don't have actual numbers for the PCV or delay...

www.st-owners.com

 

[Bozo]

Oh, how's so?

Rear brake master cylinder to rear caliper AND to delay valve to front calipers and to SMC (to PCV and rear caliper).

The ST1300 brake simulator, found here: https://mjc-506.github.io/st1300braketoy/ is a visual representation so that those tough to understand words aren't necessary.

 

[draser]

Thanks guys, I've learned something today!!

 

[MidLife]

It’s called a linked braking system. When you depress the rear pedal, 2? pistons in the rear caliper are activated and push on the pads, and 1 or 2 pistons (not positive of this but something like this) in the left front caliper is activated which also activates the smc.

One easy way to remember: The rear activates the three middle pistons.

Then in turn the left front middle will cause the two rear outers to engage via the SMC.

 

[OldMcClelland]

I love this system! It works like a charm, especially when one is tired and doesn't brake perfectly. This compensates well, safely slowing the beast.
I'll gladly service it for what it gives in return.
rob

 

[MidLife]

I love this system! It works like a charm, especially when one is tired and doesn't brake perfectly. This compensates well, safely slowing the beast.
I'll gladly service it for what it gives in return.
rob

Still there on some of Honda's newer rides, but ECU modulated (like on GWs and VFR1200) with their C-ABS system, No more SMC and PCV.

 

[Larry Fine]

 

[jfheath]

It’s called a linked braking system. When you depress the rear pedal, 2? pistons in the rear caliper are activated and push on the pads, and 1 or 2 pistons (not positive of this but something like this) in the left front caliper is activated which also activates the smc. When you press only the front brake, the smc is activated which then activates the 3rd piston on the rear caliper. I know, terribly complicated and completely unnecessary IN MY OPINION. A huge source of problems that should have never been put on this bike. Again in my opinion, the weakest and most problematic of all the components and systems on this bike. But when working properly, it is incredibly effective and powerful, and works very well as it was designed.

I cannot let that go unchallenged ! I did try, and I sat on my hands for a few minutes with steam coming out of my ears.

I realise that you added caveats and said: "something like this" and "in my opinion" which makes it very clear. But I thought -- Someone will read that and believe it - or worse - some AI search engine will pick it up and treat it as fact. "Having a halucination", I think they call it.

Anyway, since you don't know I thought I'd tell you. Sorry, I cannot help it.
Actually the VFR has a similar system which is plumbed differently from the ST1300 - but oddly, in a similar way to the way that you - sort of - describe.

So for the ST1300:

When you press the rear pedal 5 pistons are operated when the bike is in the garage.

1. The rear centre piston is activated by a direct line from the rear pedal master cyclinder.

2&3. The front left and front right centre pistons are activated (the front right once a certain pressure has been reached).
So the rear pedal operates the 3 centre pistons directly. Nothing else affects the centre pistons.

4 & 5 The fluid pressure moves through the SMC from behind the primary seal and activates the 2 rear outer pistons.

The Front Brake lever operates the 4 outer pistons on the 2 front calipers, directly.

When the bike is moving and the rear pedal is pressed, the same happens - but this time because the bike is moving, the front left brake grabs the rotating brake disk and moves the left caliper bracket forward. It pivots on a needle roller bearing in the front fork leg. Only by 1-2mm, but it moves. This operates the secondary master cylinder which applies pressure to the 2 rear outer pistons.
So again, the rear pedal operates the three centre pistons directly and also causes the SMC to operate the 2 rear outer pistons. (Whether the movement of the SMC or the pressure from the rear pedal causes the rear outer pistons to be applied - I don't know. It will be determined by which one is applying the most pressure.) The SMC does apply a phenomenal amount of force if you brake very hard. It is like power assisted braking - but it is regulated. There is a safety mechanism that won't let it apply too much. (The proportional control valve). Assuming that the Compensation ports are all clear.

When the bike is moving the front brake lever operates its own 4 front outer pistons, and because the braking front left caliper activates the SMC, it also moves the 2 rear outer pistons.

I do agree with your last statement - when it is working properly it is incredibly effective and powerful, and works very well as it was designed.

I for one am glad that this bike has this system. The biggest problem may be to do with the people who service them. Some people know nothing about how they work and the important stuff is not known about.

If it is not serviced properly then it is possible for pressure to build up in the rear line and the rear brake will lock solid. This doesn't happen just out of the blue. There is a long build up to it.
And then - 'suddenly' it happens.

It's like traffic lights: "It was green officer. I kept checking as I approached. It was green, it was green, it was green, ..... etc ......, it was green. And then suddenly it went red, and I couldn't stop in time." Did he expect it to stay green? Did he not think that the longer it was on green, the greater the liklihood that it would turn red ?

 

[Art Franz]

I cannot let that go unchallenged ! I did try, and I sat on my hands for a few minutes with steam coming out of my ears.

I realise that you added caveats and said: "something like this" and "in my opinion" which makes it very clear. But I thought -- Someone will read that and believe it - or worse - some AI search engine will pick it up and treat it as fact. "Having a halucination", I think they call it.

Anyway, since you don't know I thought I'd tell you. Sorry, I cannot help it.
Actually the VFR has a similar system which is plumbed differently from the ST1300 - but oddly, in a similar way to the way that you - sort of - describe.

So for the ST1300:

When you press the rear pedal 5 pistons are operated when the bike is in the garage.

1. The rear centre piston is activated by a direct line from the rear pedal master cyclinder.

2&3. The front left and front right centre pistons are activated (the front right once a certain pressure has been reached).
So the rear pedal operates the 3 centre pistons directly. Nothing else affects the centre pistons.

4 & 5 The fluid pressure moves through the SMC from behind the primary seal and activates the 2 rear outer pistons.

The Front Brake lever operates the 4 outer pistons on the 2 front calipers, directly.

When the bike is moving and the rear pedal is pressed, the same happens - but this time because the bike is moving, the front left brake grabs the rotating brake disk and moves the left caliper bracket forward. It pivots on a needle roller bearing in the front fork leg. Only by 1-2mm, but it moves. This operates the secondary master cylinder which applies pressure to the 2 rear outer pistons.
So again, the rear pedal operates the three centre pistons directly and also causes the SMC to operate the 2 rear outer pistons. (Whether the movement of the SMC or the pressure from the rear pedal causes the rear outer pistons to be applied - I don't know. It will be determined by which one is applying the most pressure.) The SMC does apply a phenomenal amount of force if you brake very hard. It is like power assisted braking - but it is regulated. There is a safety mechanism that won't let it apply too much. (The proportional control valve). Assuming that the Compensation ports are all clear.

When the bike is moving the front brake lever operates its own 4 front outer pistons, and because the braking front left caliper activates the SMC, it also moves the 2 rear outer pistons.

I do agree with your last statement - when it is working properly it is incredibly effective and powerful, and works very well as it was designed.

I for one am glad that this bike has this system. The biggest problem may be to do with the people who service them. Some people know nothing about how they work and the important stuff is not known about.

If it is not serviced properly then it is possible for pressure to build up in the rear line and the rear brake will lock solid. This doesn't happen just out of the blue. There is a long build up to it.
And then - 'suddenly' it happens.

It's like traffic lights: "It was green officer. I kept checking as I approached. It was green, it was green, it was green, ..... etc ......, it was green. And then suddenly it went red, and I couldn't stop in time." Did he expect it to stay green? Did he not think that the longer it was on green, the greater the liklihood that it would turn red ?

Thank you for your (as usual) very clear explanation of what happens when you activate the brakes on an st1300. Hopefully that will clear up any confusion or quoting-as-fact-when-it-was-actually-the-ramblings-of-a-white-haired-st1300-enthusiast-that-couldn’t-be-bothered-to-source-and-describe-accurately-the-workings-of-said-st1300-motorcycle-braking-system by any AI bots that may have their attention drawn to my less-than-factual-rambling. There, now let’s see how the bots do with that

 

[Larry Fine]

I don't know if anyone else needs this explanation, or if I have it totally correct, but as I understand it:

If the SMC can be rocked noisily back and forth (in the rotational direction), it's because the piston is frozen in the bore. This means the pressure to the rear caliper never fully releases, causing the rear brake to drag. It also means the rear brake is not being applied by the SMC.

The concern is that one strong jab on the front brake could drive the frozen piston farther in, where it might remain in the new position, possibly locking the rear brake permanently. That's the rear-wheel locking-up risk that Larry has been trying to warn us about. If I grasp it right.