SMC Failed

cjames431

cjames431

Joined
Oct 17, 2014
Messages
888
Location
Tacoma, Wa
Bike
2010 ST1300
I replaced the SMC at ~60k miles and now my rear brake is dragging at 130k miles.
I flush the brake system every 12-14k miles.
I just ordered the second replacement SMC. Is 60k all I should expect to get or is there something else I am missing?
 
You'll probably get a lot of different answers, but my SMC was replaced at 150,000 miles. It never locked up the rear wheel, but it did grind down the rear rotor such that I had to replace it.l
 
cjames431 said:
I replaced the SMC at ~60k miles and now my rear brake is dragging at 130k miles.
I flush the brake system every 12-14k miles.
I just ordered the second replacement SMC. Is 60k all I should expect to get or is there something else I am missing?
Click to expand...
There are several things that can cause an SMC unit to fail, just changing the fluid every so many thousand miles, will not assure that yours will remain in good health.
There are also several other things, that can cause the rear wheel to drag, and give symptoms like a failing SMC unit.
If your free tomorrow, give me a shout on the white courtesy phone and we'll go over a few of them for you.
:WCP1:
 
Since they fail due to some type of corrosion from environmental affects, and since you do live in a place that gets lots of rain - assuming you ride in the rain a lot. That can be part of the issue. Even not riding can be an issue. They are designed with drainage channels - pre 2008 has a small hole if I remember correctly and 2008 and newer have a slot to allow water to escape. But, there's probably some left there all the time after some inclement weather...

I wonder if some type of flexible rubber boot over that would be good for keeping water out.....
 
It may not be the SMC. The rear master cylinder may be at fault, the caliper pistons or caliper slides may be sticking. I’m sure a call to Larry will get you pointed in the right direction.
 
cjames431 said:
I flush the brake system every 12-14k miles.
Click to expand...
Honda specs a fluid change by time, not miles. Brake fluid is hygroscopic - it absorbs moisture from the air. If your humidity is high in Tacoma, you should probably be flushing the system yearly. If you are changing the fluid every year to two years, then you might have just gotten a bad SMC - assuming it is not another problem.

Did you do the tests to ID that the SMC is causing the dragging or did you make an assumption and order the part?
 
I could be wrong, and often am, but under normal conditions (whatever normal is), with regular riding, I would expect a properly working SMC to essentially last the life of the bike.

I got my '08 after my brother in law let it sit in his garage untouched for 3 or 4 years.

In my (non-experienced, non-professional) view the SMC is not a wear item, and with the recommended brake fluid flush intervals, should basically last the life of the bike.

No doubt I will be corrected if required.
 
I ride year round so there's no dormant period. Fluid change is yearly as I average 13-14k miles a year.
Yesterday, when I got home the rear disk was to hot to touch while the front was cold. Once the bike sat for a few hours the rear wheel spun freely. Which was a change from sitting at work. I moved the bike to leave work and it was like I was pushing against a flat tire.
I'm also at the end of useful life on my rear brake pads which I failed to check while the rear wheel was off.
 
Mellow said:
Since they fail due to some type of corrosion from environmental affects, and since you do live in a place that gets lots of rain - assuming you ride in the rain a lot. That can be part of the issue. Even not riding can be an issue. They are designed with drainage channels - pre 2008 has a small hole if I remember correctly and 2008 and newer have a slot to allow water to escape. But, there's probably some left there all the time after some inclement weather...

I wonder if some type of flexible rubber boot over that would be good for keeping water out.....
Click to expand...

I second that first statement. The rubber boot on the ST1300 SMC is pretty sound. The same arrangement does a perfectly good job on the brake and clutch lever, and the rear pedal MC has a very similar arrangement - except it of course is facing down.

The rubber boot is an excellent idea. Must get one !!!

My issue with the boot is more to do with the people who - alarmed at the possibility of water gettting in - lift it and apply silicone grease, without realising that it is extremely difficult to get it to seat again, and impossible to tell whether or not it has sealed properly.

More info on this here:

Article [13] - ST1300 - Brake Maintenance - 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 www.st-owners.com
 
Money well spent? I’d call it risky.
When the pads get that thin, they can break apart and damage all kinds of stuff, including the rider.
They look pretty dirty as well, which makes me wonder the condition of the calipers, pistons, and guide pins etc.
 
What I have done is apply silicone grease to the outside of the boot and in the channel so water can't get trapped in the grooves and sit there. I wipe this out every year with some q-tips and apply new grease. This acts like a rubber boot of sorts. Simple to do as a preventative maintenance item. Seems to be doing the job.
 
When I replaced my last smc, I noted the accumulation of a significant amount of pasty crud on top of the smc's piston, at the contact point with the pushrod and the retention washer. It prevents the piston from retracting fully, and thus pressure is not relived in the rear circuit. It is a mash of brake dust, water, and perhaps some brake fluid residue. This dust enters at the top of the pushrod,,, and certainly if the oem boot is damaged. If I see the same corruption on my next smc inspection,,, I will likely employ some silicone brake grease to attempt to reduce the contamination. I have also considered adding a secondary outer boot at to the pushrod fork,,, to shield against dust and water,,, but I have not got there yet. Good thread,,, great and important idea's,,,, CAt'
 
Igofar said:
Money well spent? I’d call it risky.
When the pads get that thin, they can break apart and damage all kinds of stuff, including the rider.
They look pretty dirty as well, which makes me wonder the condition of the calipers, pistons, and guide pins etc.
Click to expand...
The pistons have a lite coating of brake dust, the pin is in need of cleaning and there's a bit of accumulated road grime on the caliper. All will be cleaned and have a fresh dab of anti seize applied at reassembly. The brake stop pin is clean and still has a clean layer of anti seize.
I inspected the stop bolt hole in the bracket and there's no rifling.
 
Last edited:
I have seen, inspected, and repaired several failed SMC units, that the owners tried to "protect" by stuffing grease under the boot, only to have it collect all kinds of crap jamming things up.
From the factory, the pre-assembled SMC units, have a very small amount of silicone grease between the ball end of the push rod, and the seat of the piston. This is to make sure these two parts have smooth movement between them.
By adding more grease to this area, you are simply risking road grime getting into this area, and the brake dust turning into lapping compound etc.
Dirt and stuff sticks to grease making things worse, not better.
Too much grease also can work itself down into the SMC unit itself and contaminate the brake fluid etc.
I've seen folks spray WD40 in this area, thinking they are doing a good thing, only to find they destroyed the SMC in very short time.
The same thing goes for the brake pad retaining pin, if you want to prevent the pads from moving correctly, coat these with a lot of grease, and watch the crap start to gather, preventing smooth movement.
Clean/Dry is often better, or a very small amount of Antiseaze in two very small strips just where the contact points are, will keep this area clean and working correctly.
 
Igofar said:
I have seen, inspected, and repaired several failed SMC units, that the owners tried to "protect" by stuffing grease under the boot, only to have it collect all kinds of crap jamming things up.
From the factory, the pre-assembled SMC units, have a very small amount of silicone grease between the ball end of the push rod, and the seat of the piston. This is to make sure these two parts have smooth movement between them.
By adding more grease to this area, you are simply risking road grime getting into this area, and the brake dust turning into lapping compound etc.
Dirt and stuff sticks to grease making things worse, not better.
Too much grease also can work itself down into the SMC unit itself and contaminate the brake fluid etc.
I've seen folks spray WD40 in this area, thinking they are doing a good thing, only to find they destroyed the SMC in very short time.
The same thing goes for the brake pad retaining pin, if you want to prevent the pads from moving correctly, coat these with a lot of grease, and watch the crap start to gather, preventing smooth movement.
Clean/Dry is often better, or a very small amount of Antiseaze in two very small strips just where the contact points are, will keep this area clean and working correctly.
Click to expand...
Kinda like too much lube on your chains drive bikes. Collects and holds the sand and dirt. Years ago we would leave the chains dry when riding in sand and clean after riding.
 
MI-St1300 said:
What I have done is apply silicone grease to the outside of the boot and in the channel so water can't get trapped in the grooves and sit there. I wipe this out every year with some q-tips and apply new grease. This acts like a rubber boot of sorts. Simple to do as a preventative maintenance item. Seems to be doing the job.
Click to expand...
This makes a lot more sense than a boot over the area. Because a boot over the area will still trap moisture inside itself, especially in the environment of Tacoma.
 
You must log in or register to reply here.
Back
Top Bottom