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

[Bob H]

Drained brake fluid and disconnected the SMC. Piston is stuck solid. Any hope is out the window as the bore is bound to buggered if that seized up.
On the plus side, no faffing about with repair kits that might not work anyway.

 

[jfheath]

Good decision.
Take the opportunity to find out about how this thing works if you can.

In particular the fitting of that top hat shaped rubber boot, and seating it properly.
The only time you really get time to practice without risking damage with no serious consequences, is when you have a duff unit in your hand.

Article [13] - ST1300 - SMC Boot Fitting - A Cause of Failure ? | ST1300 Articles

The rubber boot on the ST1300 Secondary Master Cylinder is designed to keep water out. Unfortunately, since you cannot see what you are doing when fitting the rubber boot, it is entirely possible that casual maintenance can result in allowing water to be let in. I made reference to this in the...

www.st-owners.com

Also - that gauze filter is not obtainable as a spare part, but if you are lucky, they can be removed, taken apart and kept as a spare. You may find this interesting.

Article [13] - ST1300 - Maintenance - Photos of dismantled SMC | ST1300 Articles

A faulty SMC, taken apart, sawn lengthways, with labelled photos and a commentary. This SMC had a brand new service kit fitted not long before it failed again. A while ago I posted a query concerning some weird behaviour on a friends braking system. The symptoms were that in spite of getting...

www.st-owners.com

 

[Bob H]

Hi John,
SMC ordered. I quoted the VIN number of my bike and although 2007 reg it is a 2006A model so you were bang with the part number.
Syphoned out the fluid with a hand vacuum pump which worked OK apart from some air being drawn in on a couple of nipples which was sorted by a drop of LX plumbing sealant smeared around the nipple and left to set for 5 mins, peels of easy enough when done with. Just need to wait for the part to be delivered.

 

[jfheath]

Good stuff - so you managed to have the bike for which they have the part in stock ? That is definitely the model of bike to own.

In my vast experience of one, the assmbled part comes with some silicone lubricant applied under the rubber boot. Unless you have mastered the art of getting the brim of that top hat rubber boot seated while everything is in place, I would leave it well alone, becasue as it is, it will be seated correctly. If you disturb it and then you don't seat it properly, (and you cannot see whether it is or not), then it will let water in.

You will need new crush washers - 2 for each the banjo unions - go to a dealer they buy copper ones by the hundreds.
I took the precaution of measuring the length of the pushrod in its fully extended position. (I think you did the same in one of your photos). That way, If I need to take the bracket off the end, I can put it back together exactly as it was.

The SMC comes with two white nylon plugs fitted. They look like an integral part of the assembly - a special sort of seal for the Banjo bolts maybe ? No - they are just plugs to keep out the moisture when in storage. Take them out and keep them on one side. They may come in handy. Oh, ye gods, my Dad has been dead for 22 years, and I still can't get rid of the 'it may come in handy' gene. Nice to be reminded of him though.

 

[Bob H]

Noted on the aforementioned. My local Honda dealer is 40mile away but I can get an assorted box of bango washers for £8 from Halfrauds which is a dearer way of doing it but they are local. Used to sand and heat them to soften and expand them in the bad old days. Never had a leak either, but can’t be arsed with all that nowadays.

 

[jfheath]

Goodridge Copper Crush Washers

These copper crush washers are essential when replacing/fitting chrome plated steel, mild steel and stainless fittings such as banjo bolts and hose fittings ensuring a correct, fluid tight seal.Crush washer sizes: -03 (3/8

www.demon-tweeks.com

Link doesn't take you to the page. Enter "Crush Washers" into the search bar
I bought 100. Just choose the size.

 

[Bob H]

I should have the SMC delivered to me tomorrow (Friday) so hopefully should have the bike back on the road for Sunday for a test ride. Should have it fitted and bled in a day right.
I have had the loan of my brother in laws Honda deuville in the meantime which is good of him but after riding the Pan a deuville feels bit agricultural with having 2 pistons. It don’t like pulling away in 2nd gear much either.

 

[Bob H]

SMC arrived but was delivered two houses away as the part supplier put the wrong house number.
Part fitted and pulled the new fluid in using a hand vacuum pump but I couldn’t pull fluid out of the bleed nipple at the PCV or rear calliper. Not sure if this is to do with PCV or not. I did think at one point that perhaps the PCV was knackered as well. I decided to bleed the whole system again by pumping the cylinders this time, well the wife pumping the cylinders and me operating the bleed nipples, and I managed to get loads of air out of the PCV and rear calliper. Went out for a test ride and all seems to work as it should and no leaks.
I haven’t tried stripping the SMC as the circlip is well in there and the two 8mm bolts rounded even though using a 6 sided socket.
At the end of the day I’m just glad to have the bike back on the road.
Seems to me that the hand vacuum pump is good for emptying the lines and initially filling back up but to get all the air out pumping the cylinders s more reliable.
Thanks for all the advice given.
Next job respraying the tatty looking fuel cap.

 

[C110]

Is there a way to see if the brake fluid in the system is not blocked is this possible to check without the piston removal?
Is there a screen to clean also i read somewhere?
Thx Steve

 

[MidLife]

Is there a way to see if the brake fluid in the system is not blocked is this possible to check without the piston removal?
Thx Steve

Hey Steve,

The answer is YES, of course.

But this is your first post so better leave the experts here advise you on that.

Also, expanding on what problem the bike is experiencing might help deciding on best course of action.

 

[C110]

Problem is brakes front not come free complete afther cleaning and bleeding everything
Can do one turn almost with a good push on wheel
This without ride afther put everything together.
What is the function for the smc(second master cylinder)?The bike had also problems before with the rear brake unfortunately
I bought the bike like this.No history but it is a 2006 A6 europe model 41000km not miles.

 

[MidLife]

Problem is brakes front not come free complete afther cleaning and bleeding everything

So your current issue is with the front brakes?

The SMC (Secondary Master Cylinder) energizes the rear outer pistons when the front brakes are engaged. It is how the front and rear brakes are linked.

What were your rear brakes issues and how did you fix them? Did you do the work yourself?

 

[C110]

I make a testride tomorrow and update the situation
The rod from the SMC is very hard to push in is this normal?
I would like to clean the SMC and know if there is a tiny hole that can make problems for example when blocked
I did the seven steps in the right order to bleed the brakes and cleaned the pistons in the calippers also..

 

[Igofar]

Sounds like your SMC has failed, attempting to clean and rebuild it probably won’t fix things, the entire unit should be replaced, and your rear caliper bracket should be inspected as well.
What brand pads are you using?
You can verify if the piston is jammed up, which means the filter cartridge is probably clogged as well.

 

[C110]

Thx Igofar
tommorow i try to open the SMC if the testride is not good.
The dust rubber is it easy to pull away to remove the difficult clip to get the piston out?

 

[C110]

brake pads front from model 2006 that don,t come complete free
not original brand unknown

 

[Igofar]

The service manual warns you NOT to open the SMC unit up.
Doing so you could cause more issues not getting the depth correct.
You can verify if the piston is dragging or stuck in the bore, by opening the PCV and place a bleed tube on it, then manually pushing the piston down into the bore. If it is working correctly it should push in smoothly, and retract, about 1/2 inch or so.
If the PCV is open and you can’t gently push the piston in its entire length, you have your answer.
I would caution you not to ride your bike with these issues.

 

[mdee]

The service manual warns you NOT to open the SMC unit up.
Doing so you could cause more issues not getting the depth correct.

I have read a few threads about SMC depth adjustment. But I have not seen on SMC parts where an adjustment can be performed.
I bought and installed SMC piston set 45620-MCS-G04. I found no adjustment possibilities with the part.
Anybody have pictures showing how an SMC part can be adjusted?

 

[Andrew Shadow]

Anybody have pictures showing how an SMC part can be adjusted?

Underneath the rubber boot is what is basically a threaded rod that allows adjusting the distance that you see measured in the below photo courtesy of @jfheath.
This distance is fixed at the factory during assembly and altering it is not recommended.

 

[jfheath]

The above photo of a service kit show the bracket which the mounting bolt passes, and which screws into the captive nut on the other side.

This entire black bracket is screwed on to a thread until it meets a locknut - which you can see - the shiny bit of metal between the bracket and the rubber boot.

This isn't there for adjustment. It is factory set.

I did have cause to remove this once. I took the precaution of measuring the length before disassembly using a caliper with a vernier gauge accurate to a hundredth of a mm. Not a digital one - they are not accurate enough, even if they do show 3 decimal places.

When I put it together again, even though the locknut had not moved, the reading was wrong. I took it apart, cleaned the faces and reassembled. That was correct.

The factory setting is correct for the positioning of the primary seal in relation to the tiny compensation port. There is nothing to adjust. If you disturb it and get it wrong, you will probably end up with a rear wheel lockup.

The warning should be taken seriously. Don't mess around with it. If you are at the stage where you think that some adjustment is necessary there are two things to say
1. You are wrong
2 . You should get a new smc.

Where are these threads which mention SMC adjustment? Not on this forum surely?
Do yourself a favour and close your account. It sounds like they have no idea what they are talking about.