test for a faulty SMC?

Joined
Apr 7, 2013
Messages
16
Location
Rochester, MN
Bike
2004 ST1300A
After pulling the bike from winter storage and mounting new tires, I noticed the rear brake dragging. I can't find specific answers from searching the forum. If they exist, I apologize in advance. My question is twofold:

1. Is there a surefire test to diagnose a failing secondary master cylinder (SMC)?
2. Can the new version of the SMC issued in '09 fit my 2004 ST1300A?

Here is some background info if it is helpful for diagnosis. I have cleaned the pistons externally with the wheel off to remove any road debris. I coated the shiny pistons with brake fluid before pressing them back into the caliper. I was able to press the center piston back into the caliper with hand pressure. I am not able to push the remaining two pistons (operated by the SMC) without c-clamps. The front and rear pads were replaced in September, 2014 at 23,000 miles when the fluid was also replaced. Current mileage is 34,000.

Now preparing for information download :)
 
Joined
Nov 10, 2007
Messages
1,608
Age
61
Location
Vancouver, British Columbia, Canada
Bike
1&2 2005 ST1300ABS's
STOC #
8562
Here is a great article about testing the brakes.
I read it once a year as it has so much information on our braking system.
Thanks John for such a great article.
Also, I would go out and ride it around the block a few times as a bit of corrosion on the rotors might cause a slight drag if the bike has been sitting for some time. I have a infra red heat gun to check the rotors to see if one or the other is developing more heat.

https://www.st-owners.com/forums/content.php?211-ST1300-Brakes-Avoiding-the-Pitfalls
 
OP
OP
Dccoleman
Joined
Apr 7, 2013
Messages
16
Location
Rochester, MN
Bike
2004 ST1300A
Many thanks to Larry (Igofar) who spent an hour or so on the phone helping me with my dragging rear brake. Thanks to him I feel confident I have a failing SMC.

I should not be able to engage the rear outer cylinders by pressing the foot pedal alone while the bike is stationary. Larry surmises the SMC piston is stuck, allowing the brake pedal to charge fluid through the SMC all the way to those two cylinders in the rear. He also explained how the SMC bore can often get out of round over time. As I understand it, this is why a new piston from a rebuild kit will not always work. I have chosen to replace the SMC assembly which includes a new piston and bore rather than running the risk that a new piston alone from the rebuild kit wouldn't work properly in my existing SMC bore.

I ordered the SMC assembly, Honda P/N 06454-MCS-G03 from discounthondaparts.com ($133.55 shipped) along with four crush washers (Honda P/N 90545-300-000 $10) and a check valve bleeder from motion pro ($11 from Amazon). I'll update once the parts have been installed and I've tested the system.

Thanks to everyone. I hope this info helps the next guy.

David
 

dduelin

Tune my heart to sing Thy grace
Site Supporter
Joined
Feb 11, 2006
Messages
9,640
Location
Jacksonville
Bike
GL1800 R1200RT NC700
2024 Miles
006739
STOC #
6651
I just checked my ST1300 whose brakes are in excellent working order. The rear wheel can be turned about 2 turns with a quick press of the foot. I then gently moved the rear outboard pad against all three pistons to gain approximately 2 mm clearance between all three pistons and the pad. I pressed the rear brake pedal hard once. Checking the piston clearances I had just opened - after pressing and releasing the foot pedal all three pistons press against the pad, removing the 2 mm clearance in all three, foot brake alone. I checked the rear wheel again and get about 2 turns. Rear caliper is operating normally.

Then I checked the SMC for free play against the fork leg with a digital caliper. The left front caliper can be pressed about 2 mm forward thus actuating the SMC. The caliper has free movement back and forth this 2 mm upon release. SMC is free and clear. Check rear brake again - still get two turns of rear wheel. I laid a blanket down on the floor adjacent to the left side of the bike where I could press the left front caliper against the fork leg, thus compressing the SMC again. With the bike on the centerstand and holding pressure against the SMC I try and turn the rear wheel with my foot and am not able to. SMC is pressing the rear pads against the disk. I release the SMC and the rear wheel turns freely. SMC is working normally in this test sequence.
 
Last edited:
Joined
Feb 19, 2012
Messages
83
Location
Patchogue, NY
Bike
ST1300 - Black
In the passed, I had to learn the SMC problem too. I knew my SMC was failing, due to the burn smell of brakes, when stopped.
The tricky part of this repair, is the bleeding of the lines.
I had to do my bleeding procedure 3 times before I felt I did it right.
 
Joined
Mar 21, 2017
Messages
51
Location
Park City, Utah
Bike
2010 st1300abs
Many thanks to Larry (Igofar) who spent an hour or so on the phone helping me with my dragging rear brake. Thanks to him I feel confident I have a failing SMC.

I should not be able to engage the rear outer cylinders by pressing the foot pedal alone while the bike is stationary. Larry surmises the SMC piston is stuck, allowing the brake pedal to charge fluid through the SMC all the way to those two cylinders in the rear. He also explained how the SMC bore can often get out of round over time. As I understand it, this is why a new piston from a rebuild kit will not always work. I have chosen to replace the SMC assembly which includes a new piston and bore rather than running the risk that a new piston alone from the rebuild kit wouldn't work properly in my existing SMC bore.

I ordered the SMC assembly, Honda P/N 06454-MCS-G03 from discounthondaparts.com ($133.55 shipped) along with four crush washers (Honda P/N 90545-300-000 $10) and a check valve bleeder from motion pro ($11 from Amazon). I'll update once the parts have been installed and I've tested the system.

Thanks to everyone. I hope this info helps the next guy.

David
IgoFar is the man! It is truly great to have people like him that have such a strong passion for our bikes and the willingness to freely give their knowledge to interested members!
 
Joined
Jan 8, 2011
Messages
7,062
Location
Arizona
Bike
2007 Honda ST1300A
I wish I had a nickel for every time I heard someone say "my brakes are in excellent working condition". I have at least three failed SMC units sitting on the workbench as I type this. To be fair, one person didn't think his brakes were working correctly (he was right) the other two insisted that the brakes were fine, and working perfectly. Once they were removed, opened up, and inspected, the damage (wear) was plain to see. After new parts were installed, the owners could not believe how well their brakes worked again, and even commented on how they had no idea how bad they had gotten over the last year or two since the brake system was flushed or serviced.
Some folks claim to have bikes that their clips never break, their hoses never leak, parts never fail, secondary master cylinders last for 200 thousand miles without service, and their suspension is dialed in good enough to be a grand prix racer, but alas, for the rest of us mere mortals, we should service our bikes often, replace coolant hoses every few years, flush our brakes, and not just assume that are brakes are in excellent working condition just because they have gotten use to how it operates.
when a person suspects that his SMC is causing brake issues, and the part is 13 years old, why would anyone stir the pot and suggest that it may be working normally? I think it was wise of our OP to replace the entire unit, to err on the side of caution since these bikes are prone to failures in this area.
 

Andrew Shadow

Site Supporter
Joined
Jan 28, 2012
Messages
5,069
Location
Montreal
Bike
2009 ST1300A9
I may have misunderstood Dave's response in post # 6 above but I thought he was writing that the results he described are normal when the brake system is subjected to the test procedure that he outlined. I didn't understand him to say that the OP's SMC condition was normal. I took it to be him responding to the OP's request for an SMC test procedure by describing his procedure and the expected outcomes. As the brakes are an important mechanical system and the SMC is known to be a weak point I would like to know if I missed something?
 

dduelin

Tune my heart to sing Thy grace
Site Supporter
Joined
Feb 11, 2006
Messages
9,640
Location
Jacksonville
Bike
GL1800 R1200RT NC700
2024 Miles
006739
STOC #
6651
I may have misunderstood Dave's response in post # 6 above but I thought he was writing that the results he described are normal when the brake system is subjected to the test procedure that he outlined. I didn't understand him to say that the OP's SMC condition was normal. I took it to be him responding to the OP's request for an SMC test procedure by describing his procedure and the expected outcomes. As the brakes are an important mechanical system and the SMC is known to be a weak point I would like to know if I missed something?
I was replying with an objective field test procedure to diagnose a stuck SMC. Nothing more, nothing less. An operative SMC will not pass the field test which was the OPs #1 question.
 
Joined
Jan 8, 2011
Messages
7,062
Location
Arizona
Bike
2007 Honda ST1300A
The problem with explaining how to perform the secondary master cylinder test is, not everyone understands how to do this test correctly. While you may or may not understand how to do this test, I have seen folks do this test incorrectly more often than not, and then operate their bikes in an unsafe condition, thinking that their secondary master cylinder "passed the test", just because they could force the rear wheel to lock up. When pressing the unit in a forward and upward direction, to check to see if the rear wheel will turn or not, this should be done with the same amount of pressure as one would use to operate the front brake lever to activate the brake. I have see people use both hands, and lean their entire body weight into the unit with enough force to almost push the bike off the center stand, and then think that because the great amount of force applied caused the rear wheel to SLOW down, and then finally stop, that their unit passed this function test! Even a failing or damaged secondary master cylinder CAN be forced to stop the rear wheel from turning by using brute strength. This does not mean that the brakes could be in excellent working condition, this could simply mean that the person performing the test either may not understand how to do the test correctly, or the person it was explained to did not understand how to do the test correctly. Brake Issues could be a very serious concern when operating incorrectly, so I think it would be very wise to err on the side of caution, and replace a unit, (that has a history of known failures) that is thirteen years old, with an unknown history of service, rather than taking the chance that the safety check was done/explained/understood correctly.
Again, I think it is a very good idea that the OP is not taking any chances with his brakes, and chose to replace this part rather than guess that he did or understood the test correctly.
 
Last edited:
OP
OP
Dccoleman
Joined
Apr 7, 2013
Messages
16
Location
Rochester, MN
Bike
2004 ST1300A
Thanks everybody who have contributed to this post. I appreciate the expertise and experience behind all of the excellent comments. What I didn't share before, and what Dave had no way of knowing, is that I had removed the rear wheel prior to posting and was not able to perform the test while I was on the phone with Larry. The test you describe is the first thing Larry mentioned, but I wanted to move forward while I had him on the phone.

Now I understand that it is really the place to start and it is the answer to my original post. You've each provided clarity and knowledge I didn't have before and I really appreciate it. I'll post my results when I've put the new SMC on.
 
Joined
Jan 4, 2009
Messages
112
Location
The Great NW
Bike
08 VFR800, 17 CB1100
Here's my concern.... I'm not, nor will I ever be able to perform anything other than the most rudimentary of mechanical procedures on this bike. Therefore, I have to trust in the skill of certified Honda mechanics. Scary, but that's just the way it is. This SMC issue has been going on for so long, yet it seems as if there are very few people who really and truly know how to diagnose and correct it. I'd hazard to guess that the most knowledge and proficient are on this site and don't even work for Honda (like Igofar).
Many thanks to all of you who are on top of this and continue to keep us informed. My bike's currently in long-term stasis and will be returned to service in Nov. My intent is to find a good mechanic who will be able to check out my bike and determine if the SMC requires replacement, which I suspect is going to be a real challenge.
 
OP
OP
Dccoleman
Joined
Apr 7, 2013
Messages
16
Location
Rochester, MN
Bike
2004 ST1300A
Ok, I'm hoping ya'll can clear up a discrepancy. Jfheath published an indispensable article on this forum titled "Replacing the Brake Pads and avoiding the pitfalls" (rev. 09/15). In the section on page 7 he says to loosely fit the stopper bolt, torque the axle bolt (80 ft.lbs.), then torque the stopper bolt (51 ft.lbs.). The service manual says to torque the stopper bolt first, then the axle bolt.

Now given that the stopper bolt is in an oval shaped housing on the bracket, does it matter which is torqued first?
 
Last edited:
Joined
Jan 8, 2011
Messages
7,062
Location
Arizona
Bike
2007 Honda ST1300A
The stopper bolt must be torqued first (as indicated in the service manual). If the axle nut is tightened or torqued first, since the axle goes through the caliper bracket, it could lock the caliper in a forward or rearward position, causing it to bind.
By tightening the stopper bolt first, it allows the caliper bracket to self center when tightening the axle nut, thus allowing the rear caliper to float and move freely without binding.
 
Joined
Sep 3, 2016
Messages
1,041
Location
LSAC, AB & Indio, CA
Bike
2005/06/07 ST1300
I wish I had a nickel for every time I heard someone say "my brakes are in excellent working condition"
Well my rear brake pedal sucks...there, and only after I bled them, so obviously I need to do this properly another time. I am looking for the motion pro check valve to buy but no luck so far. My search continues...
 

Andrew Shadow

Site Supporter
Joined
Jan 28, 2012
Messages
5,069
Location
Montreal
Bike
2009 ST1300A9
Well my rear brake pedal sucks...there, and only after I bled them, so obviously I need to do this properly another time. I am looking for the motion pro check valve to buy but no luck so far. My search continues...
Motion Pro part number 08-0143. One of the Canadian distributors for Motion Pro is Motovan. Motovan is a very large distributor of everything related to motorcycles, ATV's, snowmobiles, etc. Any bike shop, ATV dealer, snowmobile dealer, etc. who deals with Motovan (which is most of them) can easily order it for you.
 

jfheath

John Heath
Site Supporter
Joined
Mar 18, 2006
Messages
2,786
Age
69
Location
Ilkley, W Yorkshire, UK
Bike
2013 ST1300 A9
2024 Miles
000679
STOC #
2570
Ok, I'm hoping ya'll can clear up a discrepancy. Jfheath published an indispensable article on this forum titled "Replacing the Brake Pads and avoiding the pitfalls" (rev. 09/15). In the section on page 7 he says to loosely fit the stopper bolt, torque the axle bolt (80 ft.lbs.), then torque the stopper bolt (51 ft.lbs.). The service manual says to torque the stopper bolt first, then the axle bolt.

Now given that the stopper bolt is in an oval shaped housing on the bracket, does it matter which is torqued first?
Thanks for the comment. The correct way of doing it is as per the manual - ie stopper bolt first. Personally, I loose fit (ie finger tight) the stopper bolt so that I can easily remove it and check for any binding that I may have introduced after tightening the axle. But as I say on the front page of my article - it isn't a definitive guide and anyone reading it should use their own skill and judgement and the official workshop manual. The workshop manual says to tighten the stopper bolt first - it avoids any problems which may arise from doing it any other way. (See Igofar's reply).

I will correct the article.
Link to article is here. Post #1
 
Last edited:
Top Bottom