Article [13] ST1300 - Secondary Master Cylinder Rebuild- SMC

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Great article. I can appreciate it all the more,, as I have gone through the whole smc fail and replacement process. In getting ready to rebuild my original smc,,, I noticed that the revzilla fiche for my 2004 list 4 versions of the replacement piston ass'y,, with only the 3 most recent being still available. I am guessing I would be best ordering the G04 (seem item's #20) ?? CAt'

 
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Great article. I can appreciate it all the more,, as I have gone through the whole smc fail and replacement process. In getting ready to rebuild my original smc,,, I noticed that the revzilla fiche for my 2004 list 4 versions of the replacement piston ass'y,, with only the 3 most recent being still available. I am guessing I would be best ordering the G04 (seem item's #20) ?? CAt'

Perhaps I can save you some $$$ and some frustration with your SMC project.
And before all those members who've used the rebuild kit and claimed success, jump in and flame me, let me share a couple pictures with you and a short explanation of why its a waste of money. :doh1:
The return port in the SMC body is VERY small, and behind it rests a very small filter cartridge, with yet another VERY small orifice.
I'll try and post a couple pictures (from other members) of just how small it is, and why your better off just replacing the entire unit.
While I'm no expert, I have replaced several hundreds of these units over the past few years, and its always the same....
Owner opened up the front of the unit, thought the bore was clean, and put it back together etc.
Only then to find out that no, or very little, fluid was passing through the screen(s) and port(s) to reach the PCV on the other side of the bike.
Nobody offers these parts for sale, and I would strongly suggest that nobody try to remove and/or clean this area out, due to the screens being VERY delicate, and directional.
These pictures were provided AFTER a new SMC was installed, and the old one taken apart to see what made it tick.
The small wire inserted into the rear of the cartridge is a very small E string from the lightest set available, and had to be forced into the hole (damaging it) with pliers. The piece sticking out the left of the cartridge is 3 mm of varnish and hardened crap that the string pushed out.
For your safety, just replace the entire unit and move on.Sawn-in-half.JPG
smc_08c.jpgsmc_valve01b.jpgsmc_valve02b.JPGsmc_valve03b.JPGsmc02 (1).JPGSMC Cutout Assembled 25pc.JPGInlet Port Cartridge.jpg
 

Andrew Shadow

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Plugged that tube and re-drilled the caliper for full function.
Did you simply cross-drill the rear caliper so that all three rear pistons are operated by the foot pedal?
Notice any significant difference in braking characteristics?
 

ChucksKLRST

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Stopped by my Local Honda shop, (even though I don't own a Honda any more) They had a customers 2012 ST1300 in the shop for SMC repair/replacement. They told me that it was being covered by Honda. So did Honda finely recognize the failure of their ways?
 
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Did you simply cross-drill the rear caliper so that all three rear pistons are operated by the foot pedal?
Notice any significant difference in braking characteristics?
The hole is drilled in the back of the piston cylinder. yes all pistons operate from rear brake. I would say it softens the rear brake a little. JME
 
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I don't have any pics, sorry. But it was quite easy to indentify the magic spot. a line is seen in the casing running from outer cylinder to outer cylinder to link them. I used a nut to block extra line port.
 
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Where does it relieve the pressure to, if pressed to hard....??
Wouldnt the smc put additional pressure needing to be relieved?
I thought the prop valve was off rear master cyl, not caliper??
No drawing in front of me so going from memory...lol
 
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I thought i had a hyd drawing i looked at last year when i did mine. But couldnt find it today. I dont remember any fluid exchange between circuit. No i got to find a drwng
 
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Hello
My name is Marcin and Im looking here for some help.
Last year my SMC start to be loud and sometimes lock my rear wheel.
Unfortunatelly from health issues I had to leave bike for half year in garage and few days ago I have starter a repair.

I bought 45620-MCS-G04 repair kit for SMC from Honda, dismount front left caliper, replaced parts, clean everything (including filter cartridge inside).
I dismounted rear caliper, clean and grease what necessary.
Dismounted also rear foot brake pump (rear master cylinder), clean & grease.

Now I have problem. I cannot bleed system. Whole the time rear brake leaver is spongy and soft. And what worst after using rear brake or SMC (by hand) it locks wheel and it is hard to turn it. Im reversing rear brake pads without any problem (everything is runnig smooth) and once again, using any brake and it locks the wheel.

Right now Im wondering if I put filter cartride that is mounted on front SMC in correct way. In one way it has full flow (very tiny hole and bigger one with valve), and other way limited flow (only by tiny hole).

Maybe someone can show me how it should be mounted? Full flow into the SMC, or out? I have found some topics here regarding that but unfortunately I doint understand well. I want to be sure.

UPDATE:
Below picture of correct way of installing the filter cartride.
Clipboard01.jpg
 
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Guess who installed a new SMC yesterday? I replaced the valve 4yrs ago and even following the proper @Igofar bleeding procedure the rear brake was always spongy or would fade.
 
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Guess who installed a new SMC yesterday? I replaced the valve 4yrs ago and even following the proper @Igofar bleeding procedure the rear brake was always spongy or would fade.
Something is wrong with your brake system then. Both the hand lever, and the foot pedal should be firm after bleeding in a good working system.
Have you inspected/checked the other parts of your brake system?
Have you ever removed or inspected the REAR master cylinder? I've found these need to be serviced/rebuilt from time to time.
And lastly, have you rebuilt the calipers? Removed the pistons and looked behind them? I often find jellied goop behind pistons, after folks simply cleaned what they could see, and thought they were finished etc.
Even though you may clean the body of the caliper, and polish the pistons clean, you never know what lurks behind the pistons if you don't pop them out from time to time and clean behind them! :nuts:
20190422_113354_1556742929804_001.jpg20190422_113410_1556742930485_001.jpg
 
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Something is wrong with your brake system then. Both the hand lever, and the foot pedal should be firm after bleeding in a good working system.
Have you inspected/checked the other parts of your brake system?
Have you ever removed or inspected the REAR master cylinder? I've found these need to be serviced/rebuilt from time to time.
And lastly, have you rebuilt the calipers? Removed the pistons and looked behind them? I often find jellied goop behind pistons, after folks simply cleaned what they could see, and thought they were finished etc.
Even though you may clean the body of the caliper, and polish the pistons clean, you never know what lurks behind the pistons if you don't pop them out from time to time and clean behind them! :nuts:
20190422_113354_1556742929804_001.jpg20190422_113410_1556742930485_001.jpg
I completely disassembled all 3 calipers the last time I replaced the fluid and cleaned them out. I religiously change fluid every 12k miles. I have not accessed the rear master yet. Currently the rear pedal and front lever give a nice solid feel. Once I'm done with everything and get to riding again I will let you know how it does.
Idle curiosity, why does the rear master not get a banjo bolt connection to the rear brake like the rest of the brake system?
 

jfheath

John Heath
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I didn't realise that I had contributed to this post before - but it seems to be populated with a few of my photos and diagrams - not that I mind that one bit, they just took me by surprise.


@martinpl In a post of 7th April 2020 (shown as post #57 on my screen) - you have reproduced one of my braking circuit diagrams and circled the SMC inlet port.

Underneath, you have drawn that one way valve. But you have drawn it the wrong way round !.

[edit] @martinpl has checked this out and come to the same conclusion. Post #57 is now showing the correct orientation [/edit]

I think in case anyone else looks in and thinks that your diagram is correct, you might want to put it the correct way round. Use this if you like.

1588359644024.png

More info and pics of the dodgy SMC and of the inlet port one way valve cartridge (and the above full sized diagram) are here:


Note the photo of the inlet port in the above link, taken immediately after taking off the black cover. The 'O' ring is still in place. Note that this is the side with the white gauze. The other side has a blue plastic clip-on cover. I verified this when I removed my own SMC a couple of years later - not touched since new. Mine was spotless !!

But really, if your SMC has got to the point where this valve is clogged, it really is time to replace the SMC - and learn to look after it better than the previous owner !

---------------------------------------------------------------------------------

Where does it relieve the pressure to, if pressed to hard....??
The proportional control valve sits in the braking system for the rear circuit between the SMC and the two outer pistons of the rear caliper.
The SMC operates those two outer pistons if the bike is in motion (as the SMC rocks forward whenever the front left brake is applied - which means when either the front lever or the rear pedal is operated). ie when braking, the SMC will operate the rear outer pistons. When the bike is stationary, the SMC cannot rock forward, but the fluid from the rear brake pedal will operate the outer pistons in the rear caliper. If you want to see how the circuit operates, then the diagram that @martinpl reproduced above can be found in the link below - intended for bleeding, but it shows what fluid is moving, which pistons are operated and where the fluid comes from.


Where does it relieve the pressure to, if pressed to hard....??
The proportional control valve is essentially a piston which moves inside a chamber. Normally, the piston remains closed under pressure of a strong spring. However, when braking force increases to the point where the rear wheel would be at risk of locking up, the spring gives way and gets pushed back into its chamber, relieving pressure from the rear outer pistons. It is actually a bit more complex than that, but that is the gist of it. Basically if you press too hard, the pressure is released before the brakes can lock.

This is completely different from the system which relieves the pressure from the pistons when the pedal/lever is released or due to expansion of the fluid due to heat. That is the tiny compensation port that exists in every master cylinder - the front brake MC, the rear brake MC, the clutch MC and yes, the Secondary MC.

For more information on this, see this link.


---------------------------------------------------------------------------------------
 

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Joined
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I completely disassembled all 3 calipers the last time I replaced the fluid and cleaned them out. I religiously change fluid every 12k miles. I have not accessed the rear master yet. Currently the rear pedal and front lever give a nice solid feel. Once I'm done with everything and get to riding again I will let you know how it does.
Idle curiosity, why does the rear master not get a banjo bolt connection to the rear brake like the rest of the brake system?
It does, its behind the side step panel.
 
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Underneath, you have drawn that one way valve. But you have drawn it the wrong way round !. If this is the way you have inserted it, it might explain why you are having trouble bleeding. The way that you have it, it is preventing fluid from the rear reservoir entering the SMC when the brake pedal is pressed. I think in case anyone else looks in and thinks that your diagram is correct, you might want to put it the correct way round.
Thank you for answer. I have found correct way using trial-and-error method ;) I have replaced picture with second one with correct position of valve.
 

Suraj

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Is there any quick way to get the air out after replacing the part as mentioned in the original post?

I successfully replaced the the SMC piston without having to completely remove the caliper or drain fluid from other cylinders. Only place that I have air is in the SMC. I want to avoid taking the fairing off if possible. I replaced the brake fluid with completely bleeding the system <200 miles ago and don't want to go through the process again if I don't have to. Also replaced the coolant while I was at it. Any inputs to this would be appreciated.

Everything that could go wrong on this motorcycle has gone wrong in 2020 for me. Clutch slave cylinder, rear brakes dragging and SMC not rebounding.
 
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