Rear brake middle piston dragging

[Jonnyboy750]

A bit of mid-winter caliper cleaning and general maintenance has left me with a bigger problem than when I started!

I cleaned up the rear caliper, greased the pins etc, but after refitting it the brake is constantly dragging and unrideable. It's not the SMC as I have done the lying-on-the-floor foot test and the SMC is applying and releasing the outer pistons properly. It's only when the rear brake pedal is used (and released) that the wheel starts to drag, but that's as far as my troubleshooting has got me. The middle piston was definitely moving freely after I cleaned the caliper, so it's not stuck as such.

I've spent the last 2 evenings trying to absorb all the information here - including some very useful guides - but I just can't work out what the fix is. The brake wasn't perfect before, it was rubbing slightly, but nothing like what it is now! It's my first bike with linked brakes and I now find myself longing for the simplicity of separates! Any help or pointers would be gratefully received.

 

[Igofar]

Mr. Heath may be your best bet on this one, since he is closer to you than I am, but I'll take a shot at a couple things...
First, a few questions:
1. what brand brake pads are you using?
2. what condition is the pad retaining pin in? Is the small white O-ring at the end of the pin damaged/torn/missing?
3. did you use too much grease when lubricating the sliding dowel, which can cause suction?
4. did you re-install the rear wheel in the correct sequence? Meaning, did you tighten (torque) the stopper bolt BEFORE tightening the axle nut?
5. did you clean out the grooves that the seals sit in with a small wooden toothpick?
6. are the seals (if replaced) facing the correct direction?
7. is there any damage on the rear caliper mounting bracket (spiral shaped markings where the stopper bolt sits) or wear on the front shelf where the front (silver clip) holds the foot of the brake pads? If this area is worn, it can cause the caliper to tilt slightly, binding one or more of the pistons.
8. has the entire brake system been flushed and bled correctly?
9. is the upper spring clip dislodged/crooked or replaced backwards?
Your SMC test is a little more involved than what you describe. The cartridge behind the unit (return port) may be clogged, and not allowing enough flow, which can cause all the rear pistons to do strange things.
When you have the bike on the center stand, and you place your foot on the rear wheel, and push down once (firmly) how many rotations does the wheel turn?
Your SMC may be dead/dying without you realizing it.
Message John Heath and work with him, I'm sure he'll be able to assist you.
In the mean time, I would strongly urge you NOT to try riding the bike with brake issues, as they can/have pitched riders off without warning, when they decide to lock up completely.
I will try and attach a couple pictures of some of the areas listed above.
Good luck.

 

[Jonnyboy750]

Thanks Igofar, I’ll answer what I can now and work through the rest when I have another attempt at fixing later this week!

1. OEM pads. Have also got some other new ones that I thought I’d try, but for now I don’t want to complicate matters - so I’ll stick with OEM. I did notice that only the piston side pad was worn - sliders?

2. Pad pin seemed fine. I sanded some corrosion and regreased. I’ll check the O-ring.

3. Will remove some grease as precaution, although I don’t think I applied too much

4. Yes, stopper bolt torqued before axle

5. No, I didn’t fully refurbish the caliper - I just cleaned it up

6. As above, no seals were replaced

7. I need to check this point more closely. I didn’t notice wear on the stopper bolt hole, but I do feel the caliper might be misaligned from the wear marks on the pads/disk after I did a very short test run.

8. No system flush as I wanted to avoid that for now. I did bleed through some fluid via the rear middle valve yesterday - which went fine.

9. No, the spring clip looks OK

Currently the wheel barely rotates, so counting number of rotations isn’t an option! If I separate the pads so that the wheel is free to spin and then do the foot test while activating just the SMC, the 2 outer pistons engage/disengage fine. The trouble starts when the foot pedal is pressed for the first time as that will clamp the disk but not fully release it. I thought this must mean a middle piston problem, but now I know that the SMC influences the entire rear brake when the pedal is applied, this could be a faulty SMC after all.

 

[Igofar]

If you opened ANY bleeder and bled fluid from it, you now may have air space in the circuit, as it moves from one to another etc.
You MUST flush/bleed the entire system in sequence from 1 to 7.
If your system has not been maintained correctly (often) you may have crap behind the pistons that your not able to see.
Simply pushing the pistons back inward often will drag/push crap behind the seals.
It would probably be in your best interest to replace all your seals, o-rings, boots, with new stuff and start fresh.
You may have something like this behind your pistons

 

[jfheath]

It looks like Larry has covered all of the bases. But as he said, get in touch, I'll help and we can discuss over the phone if you want. Where in the Uk are you ?

A couple of points to note.

• Don't get put off because this is your first combined brake system, or the stuff you read about doing away with it. It works very well, but it has to be maintained.
• In the garage, the SMC doesn't do anything, but the rear pedal will still operate all three pistons of the rear caliper.
• Stay with OEM pads.
• Take the pads out. Spin the wheel then as Larry's test. How well does it turn then ? There may be other issues.
• The odd wear of the pads needs addressing and is possibly a separate issue from pistons not releasing their pressure. It is often to do with incorrect movement of the caliper. While the pads are out see how free the caliper is to move into and away from the brake disc.
• Get in touch.
• Check out my avoiding the pitfalls for the issues regarding the rear caliper that are not related to brake fluid
  
  

  Article [13] - ST1300 Maintenance - Brakes- Avoiding the Pitfalls | ST1300 Articles

  A close hands-on look at the Honda ST1300 braking system. These are personal observations about the things that can go wrong, why they go wrong and what can be done to keep things working sweetly. Updated April 2020 and to address more recent observations, to include information about the SMC...

  www.st-owners.com

 

[V4 Rider]

The middle rear caliper is operated only by the Secondary Master Cylinder (SMC) on the front fork.

Riding smoothly, or using mainly the rear brake, means it never gets exercised.

If this is case it is worth grabbing the front brake occasionally to exercise the SMC / piston.

My local Most (UK safety test) report getting several bikes a year with the centre rear piston not touching the pad.

Pads have effectively worn down and moved away from static piston. Many can be cured by a hard application of the front brake on his rolling road. The rest need a caliper strip.

 

[jfheath]

Oops. I think that there is a bit of a mis-undersatnding of how the braking system of on the ST1300 works. Let me try to explain. The same applies to all models, with and without ABS.
The rear pedal master cylinder has two brake lines attached to it - two Banjo unions on one bolt. So both lines are fed from the same outlet port when the pedal is pressed. One line goes to the rear, one goes to the front. Further details are in the explanations below.

The middle rear caliper is operated only by the Secondary Master Cylinder (SMC) on the front fork.

The middle piston in the rear caliper is operated only by the foot pedal. The line heading to the rear from the rear master cylinder.

The movement of the SMC operates only the two outer pistons in the rear caliper - and the pressure applied is controlled (and reduced) as the pressure from the SMC increases to prevent the rear wheel from locking as the stopping force reduces the weight on the back wheel. This is managed by the proportional control valve which is mounted under the tank near your right knee.

Riding smoothly, or using mainly the rear brake, means it never gets exercised.

The footbrake also acts on both front caliper centre pistons. So the SMC will be operated every time you apply the rear brake.
The front right centre piston is subject to a pressure delay - which means that it isn't activated unless the pressure from the pedal is sufficient to overcome a strong spring in the delay valve on the front right fork leg. This is to prevent the front from diving when using the brake pedal during slow speed manoeuvres.
The centre piston in the left front caliper is activated immediately the rear pedal is pressed. The left hand caliper rocks forward and activates the SMC, which in turn activates the outer pistons on the rear caliper.

So pressing the brake pedal will always affect the front left caliper (centre piston) and all three pistons on the rear caliper - the centre one directly, the outer ones as a result of the SMC being activated by the front centre piston applying the brake on the left front caliper. Press harder and the front right centre piston is also applied. You may feel a very slight dip in the pedal when this happens.

If this is case it is worth grabbing the front brake occasionally to exercise the SMC / piston, they are operated only by the rear pedal.

The SMC will always be operated whichever pedal/lever you use. But the movement is very tiny - only about 1-2 mm. I believe it is better to exercise the SMC during the regular bleeding schedule when the rear outer bleed valve or the PCV bleed valve is open. This allows it to move the full stroke which I believe helps to flush out the old grotty fluid and prevent the build up of crystals and gunge.

My local Most (UK safety test) report getting several bikes a year with the centre rear piston not touching the pad.
Pads have effectively worn down and moved away from static piston. Many can be cured by a hard application of the front brake on his rolling road. The rest need a caliper strip.

"Most" ? Is that MOT ? If you never use the rear pedal, then none of the centre pistons will ever move as the pads wear down. The front brake lever doesn't act on any of the 3 centre pistons, directly or indirectly.

Nb - To complete the picture, when the bike is in the garage and is not moving, the SMC will not operate. It needs the spinning brake disc to rock the left hand front caliper bracket forward. But you can test its operation by hand.

But in this case, the rear pedal will operate all three pistons in the rear caliper !
The centre piston is operated directly by one fluid line.
The outer pistons are operated by fluid in the line to the front centre pistons. The same line feeds the SMC, and fluid will flow past the seal, back up the fork leg, through the Proportional Control Valve and on to the outer pistons.

'Flowing past the seal' sounds odd, but that is what happens. All 3 master cylinders have a cupped primary seal, which allows them to yield as a result of pressure from behind. Cupped seals only seal in one direction. This is just like the seal in a bicycle pump which allows air to pass on the upstroke to refill the tube, but prevents air passing on the downstroke, forcing the air into the tyre.
So when the SMC isn't activated, the fluid flows straight through the SMC.

 

[Jonnyboy750]

Thanks John for the additional explanation. I can't decide if the braking system was a feat of modern engineering (given it was introduced 20 years ago) or if it's a bit "Heath-Robinson"

Anyway, armed with even more knowledge I plan to have another attempt at this tomorrow.

 

[jfheath]

I think it does an excellent job of rapidly bringing a heavy bike to a well controlled halt. It is quite difficult to force the Abs to kick in, the gradual reduction of braking force on the rear wheel preventing it from locking as the braking force tries to lift it off the tarmac

The braking system doesn't like it when it is ignored in the service schedule. It bites back.

Who's this Robinson chap ?

 

[Al Gully]

Who's this Robinson chap ?

I hovered over his name and then hit the define button.

William Heath Robinson was an English cartoonist, illustrator and artist, best known for drawings of whimsically elaborate machines to achieve simple objectives. In the UK, the term "Heath Robinson contraption" gained dictionary recognition around... Wikipedia
Born: May 13, 1872, England, United Kingdom
Died: September 13, 1944, London, United Kingdom
Known for: Drawings of odd contraptions

 

[jfheath]

Thanks Al. My comment was an attempt at humour, since my name is Heath.

But others may not know of the delightfully contrived mechanical drawings that he produced.

 

[SMSW]

I hovered over his name and then hit the define button.

William Heath Robinson was an English cartoonist, illustrator and artist, best known for drawings of whimsically elaborate machines to achieve simple objectives. In the UK, the term "Heath Robinson contraption" gained dictionary recognition around... Wikipedia
Born: May 13, 1872, England, United Kingdom
Died: September 13, 1944, London, United Kingdom
Known for: Drawings of odd contraptions

Sounds like our Rube Goldberg, only on paper. Too bad Robinson did not live to see the internet and those complex machines/things/contraptions people make with balls, dominos, swinging weights, levers, etc.
Here is just one:

 

[ad.hom]

The cartridge behind the unit (return port) may be clogged

That was my first thought.

Where in the Uk are you ?

I've not seen that answered (yet) - even a rough geographic area will help. I happen to have both the 21st & 28th of this month off work, without too much planned. While John's knowledge quite simply eclipses mine, if the timing works out with what little plans I have, I'm happy to ride to you & help get another set of eyes on the problem, at least.

All I ask is the princely sum of a brew & possibly a couple of biscuits.

Of course, if you're in Lands End, John O Groats, or somewhere that involves a ferry... I'm not THAT crazy! Taking things apart & posting pictures/video's would allow Larry to not only tell you specifically why you're experiencing brake issues but also find all the rest of the faults on your bike, including the things you don't even know are wrong. If you're lucky, you'd set off his "clean garage OCD" too.

Pics/Video's is also infinitely quicker than waiting for my sorry behind to get on the bike... (OK guys, I admit it, the weather has been rubbish here and WFH for 2 years, I'm looking for an excuse for a trip )

 

[Jonnyboy750]

Success! The problem was a combination of too much grease on the slider bolt but I also don't think it was tight enough, so the caliper was slightly mis-aligned. In any case I removed all the grease including some more of the original which looked like copperslip. I used red rubber grease on that pin when I first reassembled it, but I think it's a bit "grabby", or at least my little pot of it that I've had in the garage for the last 10 years is! Silicon grease is possibly better.

I now have a rear caliper that has a very small amount of movement, whereas before it was always rigid - I think this is key. I can't quite believe it took me so long to fix, but all seemed fine on the test ride so I'm happy.

Thanks for the offers of help and suggestions. Next week I'll tackle the front calipers....!!

 

[jfheath]

With no pads in place, the caliper should move all the way across until the caliper touches (if the pistons are fully retracted), and all the way back until the other side of the caliper meets the inside face of the disc. This movement should be an easy push or pull for the full disatnce. If it tightens up, then there is a problem with the alignment of the pins, and possible with the bracket alignment. This is a potentially serious condition. It may work now, but your rear brake is in danger of locking on if this is the case.

Copper grease may have resulted in the rubber boot expanding, feeling 'floppy'. Silicone or rubber grease designed for hydraulic seals is better, as you say.
Normally, you wouldn't remove the rear caliper main slide pin - but since you have, beware the figure given in the diagram in some manuals. The correct torque is 27Nm, not 69Nm as stated on the diagram in my honda manual !

This diagram in the Honda UK 2003/2004 service manual is labelled incorrectly.



The correct torques are given at the start of the chapters, in the text and in the general information torque sections.
The table underneath isn't shown on the same page in the manual - I have pasted it in from the table at the start of the chapter.
I suspect that later editions will have corrected this error, but it is worth checking.

(The data for the stopper bolt can be found in the section on installing the rear wheel).

Just to help understand the diagram to see how the pieces fit together. The pieces shaded red slide together (note the red hole just to the left of the green pin).
The green pieces fit together.

 

[Jonnyboy750]

Yes I should say that I didn't plan on removing that bolt, but originally the caliper wasn’t sliding, so I just thought I’d get everything apart. After cleaning up the pin end of the bolt the caliper was sliding again, but in hindsight it wasn’t sliding particularly freely due to the excess grease/gunge it was picking up. I reckon that rubber boot needs replacing too.

Ideally the caliper will have a full rebuild in the near future, but it’s fine for now and in much better condition than when I started!

I’ll confess I used the torque-it-till-it-feels-right method on that bolt. I’ll check it again properly. Thanks again!

 

[jfheath]

'Torque til it feels tight' is much better than the 'Torque until it breaks' which is what 69Nm would have been !!.

For goodness sake - let us know roughly where you are. See if either of us is close enough to help - make sure you are safe.
Remember, you may only get to make a mistake with your braking system once.

Just for info, the hole that the pin slides in is a very loose fit. I find the drill bit that fits it most closely and turn it between finger and thumb - backwards - to lift any old grease out of there.
Then a visible smear of fresh goes onto the pin. Make sure you buy your new boots before removing the old. The old ones are near impossible to fit once they have had coper grease or 'normal' grease near them.

 

[ad.hom]

Success!

Congratulations!

Now I'll dream up some other reason to hop on the bike... maybe just "how difficult is it to draw obscene images in Google Location History..."

 

[Yohan]

Red rubber grease is grabby but that`s one of it`s good points. Look up all the good things it does to rubber. Especially recommended for brake areas where other grease might move where it`s not wanted .It`s a rust inhibitor too .

 

[jfheath]

Copper grease will stay put and soesn't seem to be affected by heat. The problem is that it is a mineral oil based lubricant, and that makes the 'rubber' boot swell so that it no longer forms a proper seal. You will find that when you take a rubber boot off the caliper, it is almost impossible to get it to seat in the groove again. There is too much rubber to fit. So silicon grease or rubber grease is the preferred substance for anything that comes anywhere near boots and seals.

The type of grease shouldn't make the brakes grabby. That might be due to surface rust on the brake discs; Pads still needing to bed in; something in the mechanics of the movement of the caliper preventing it (or the pads) from moving smoothly - eg ridged pad pin; incorrectly located pad spring; incorrect orientation of the pad spring; pad spring tabs on the narrow / outer strip of the pad spring is bent.

It might be that pads that are new to the the brake disc (eg new pads, or older used pads) are not quite sitting parallel to the disc surface - so that the part of the pad that meets the rotating disc first is a corner. This can be cured by taking a file to the corner of the pad material that is closest to the pad pin and putting a very slight chamfer on it. Not much, just to blunt the sharp 90 degree corner. Once the rest of the pad wears down a bit it will be ok. (A similar trick to angle the brake blocks on a push bike will stop the brakes from squealing).