SMC in action!

[STRider]

Among the things I didn't think would be an issue on my pristine 2012 ST1300A with 3,600 miles on it when I bought it in the summer of 2020 would be a non-functional SMC the likes of which seemed limited to those bikes with more years and certainly more miles than my new-to-me bike had experienced.

I was quickly schooled by reading the posts by the members of this site. And my first conversation over the White Courtesy Phone and the remote tour of my bike that ensued would reveal that my SMC was indeed frozen and in need of replacement. I performed a full hydraulic service on my bike short of rebuilding my clutch slave cylinder this past July and the improved response of the braking system is quite noticeable... from the saddle.

But in all the numerous threads, and how-to articles, no one to my knowledge has ever actually observed the SMC functioning as intended. Yeah, you can get down on your knees and squeeze the SMC in toward the fork leg to check for free movement, and you can lay beside the bike, spin the rear wheel and test that the rear brake is applied when the SMC is compressed, but I'd never seen it working during actual braking on the road.

I set out to fix that.

I scavenged a RAM® 9mm Angled Bolt Head Adapter Ball Base from my ST1100 and attached it to the bracket that normally holds the reflector on the left fork. Then with a short arm and a RAM to GoPro adapter I mounted my GoPro Hero 8 to the fork leg and set off to collect some data.

Behold! The SMC in action.

For those that will insist on seeing how this was rigged, here's that too.

Enjoy,

Tom

 

[Jevers]

Well done ✔ !

 

[etalors]

Great Job!! This is a first

 

[STRider]

?

Haaa!! Finger-fumblery... 2012. Will edit to fix. Thanks Gus

 

[Igofar]

SMC’s NOT in action!
Great video, thanks for making folks aware of what it should do!

 

[jfheath]

Thanks for the video. I've never seen that before. There's a lot more movement than I thought that there would be. By hand, I can move mine only 1-2mm.

 

[Upt' North]

Tom, I did. Enjoy it that is.
Are you the first to do this? I can't remember seeing a video of the operation before?
Thanks for taking the time fella, very informative and much easier to follow than descriptions etc.
Upt'North.

 

[nicksacco]

Hello, this is George Lucas.
I was wondering if you'd be interested in either filming or acting in my new Star Wars movie?


Hahahaha, great video sir!! Really shows how the thing works.

 

[Sadlsor]

Very clever, @STRider .
And now i have another mount point for my GoPro, too!
Genius, and well done AND thank you!

 

[SteveRP]

Thanks for the effort in getting it all set up, and showing it in real world action.
I was amazed at how much of the push rod edging had disappeared.
Doing my own SMC in a fortnights time.

 

[Igofar]

Thanks for the video. I've never seen that before. There's a lot more movement than I thought that there would be. By hand, I can move mine only 1-2mm.

While the system is under pressure, and property bled, you should only be able to move the piston about two millimeters with hand pressure, however, if you inspect a brand new unit before you install it, you see that there is almost half an inch of space to move in the bore.
The weight of the bike uses this space.
The common problem is most people read or are told it can only be moved 2mm and think a frozen one with limited movement is ok and passes the function test.
Unless a person has held and inspected a properly functioning one, they truly have no reference point.

 

[northwestparider]

Nice, thanks for the video.

 

[jfheath]

Cheers, Larry.
I think I may have been the first to actually measure that movement (on this forum anyway) so may be guilty of causing a whole group of people thinking that their locked up SMC was working properly on the basis that if 2 or 1 mm is good, 0mm must be better.

No.... that wasn't my intention. I'm going to have to set up a similar video on my SMC and compare it with the hand pressure movement.

I always assumed that there was more movements available - like there is on the brake lever when you squeeze harder, and certainly some of that is taken by pumping out the hose lines - which you can feel swell slightly as you squeeze harder.

 

[Upt' North]

Thanks for the effort in getting it all set up, and showing it in real world action.
I was amazed at how much of the push rod edging had disappeared.
Doing my own SMC in a fortnights time.

Don't think you can sneak in here without a hearty welcome young Steve me lad.
So, welcome from Northumberland, the kettles on if you're passing.
Upt'North.

 

[Igofar]

Cheers, Larry.
I think I may have been the first to actually measure that movement (on this forum anyway) so may be guilty of causing a whole group of people thinking that there locked up SMC was working properly on the basis that 2 or 1 mm is good, 0mm must be better.

No.... that wasn't my intention. I'm going to have to set up a similar video on my SMC and compare it with the hand pressure movement.

I always assumed that there was more movements available - like there is on the brake lever when you squeeze harder, and certainly some of that is taken by pumping out the hose lines - which you can feel swell slightly as you squeeze harder.

Heaven's no John, nobody was implying that you were providing incorrect information.
Your video's and articles are among the very best on the forum!
I've myself explained to many folks that the system, (while pressurized) should only move a couple millimeters as well.
I guess I should have pointed out an easier way to test the SMC that I've been using for several years now (not in the service manual)
The quickest way to verify if the piston is stuck in the bore, isn't to push the unit forward/upward, as both the service manual directs, and other forum members suggest (because that what they've either read or heard) this is simply a function test to see if the SMC is working correctly, or having difficulty working, or not releasing the rear wheel after being operated etc.
What I do, is place my check valve and hose on the PCV bleeder, crack it open, THEN either push the piston into the SMC bore by hand, or push the entire unit forward.
With the PCV bleeder open, there is no pressure preventing you from pressing the piston into the bore its entire length etc.
You can do this, and if your careful, you won't have to re-bleed the system, only top off the fluid you've lost.
However, since this is not mentioned in the service manual, and not many tech's know how to do it correctly, I've not shared it on this forum before now.
With the pressure relieved (PCV bleeder open) you should find that you can press the piston in several millimeters with gentle pressure (your only pushing against the return assist spring) and feel if the piston is sticky, binding, or stuck in the bore. If you crack the PCV bleeder open, and can't move the piston at all, you've just verified that your piston is completely stuck in the bore.
I would also suggest that folks who know nothing about the brake system, have it inspected/tested by someone who is familiar with the system for safety reasons etc.
Anyone attempting to follow these or any other instructions on the forum, should do so at their own risk.

 

[SteveRP]

Thanks for the welcome Upt' North, i'm finding the site really helpful, lots of good info.
It just so happens i lived up your end of the world, for over 5 years, back in 2005, a tiny village called Lowick.
If anybody's in the York/selby area there more than welcome to give a shout out.

 

[Catmandu2]

SMC’s NOT in action!

Great photo series,, showing why smc's need regular maintenance. My '04 smc was replaced and works great. My '12 works great,,, and I have no idea what the history is. So each will receive their 2 year inspection this winter. Is anyone else using high temp silicone brake grease under the dust boot ?? cheers,, CAt'

 

[Chris09]

Something else, great video. Guessing that the captions imply isolated front lever then pedal actuation and I'm guessing also that the speed is about the same; and moderate ordinarily encountered sort of braking; it looks to me [unless I've got it backwards and I often do] that isolated front actuation results in the furthest travel of the SMC plunger and isolated rear actuation is about half?

 

[STRider]

Something else, great video.

Thanks!

Guessing that the captions imply isolated front lever then pedal actuation

Yes

and I'm guessing also that the speed is about the same; and moderate ordinarily encountered sort of braking;

~50-55mph. The road was not clear; traffic ahead. And yes to the style of braking.

it looks to me [unless I've got it backwards and I often do] that isolated front actuation results in the furthest travel of the SMC plunger and isolated rear actuation is about half?

I would agree.

 

[Chris09]

Well for me, that's one for the ST1300 record book; I myself would have never imagined that it only travelled half as far through the valve gradient under strict pedal actuation; I've been a big fan of this braking system since the moment I read about it; this only makes it even more interesting, but.. it does lead to more...
... and I'm not gonna say it... great video