Confirming SMC is the problem

[tman]

I'm just trying to confirm the SMC is causing my rear brake drag on my 2004 ST1300A.

If I push on the SMC it will stop the rear wheel from spinning but when I release the SMC the rear wheel drags. Likewise, when I press on the rear brake pedal the rear wheel drags. From the research I have done on this site it appears I have a faulty SMC. Does this sound right?

Can the SMC bracket assy be removed from the bike and the piston set be removed & cleaned without going through the brake bleed process? Approximately 10,000 miles ago I followed the instructions in the service manual & documentation on this site to replace my brake pads & brake fluid. But, I was hoping for a short cut to try cleaning the SMC piston.

I have found the following information on this site:
45620-MCS-G03 piston set
06454-MCS-G02 bracket sub-assy
Are these the parts that most folks have used to repair their SMC?

I still have extended warranty coverage on my 04 so I'm hoping Honda will take care of this for me. But if not I wanted to make sure I was on the right track.

Thanks,
tman

 

[Mellow]

Some brake toughing is normal... is your rear brake dragging to the point it's slowing the bike?

Hitting the brakes while the bike is on the centerstand will push them into the rotor and you'll hear that if you turn it by hand.. that's all normal.

 

[sennister]

It could be the issue. I would start by doing a good bleed of the SMC part of the brakes. Some people have been able to clear up things by doing this. As for cleaning it. In my case it wasn't a case of anything being dirty. What happened was water worked past the seal, contaminating the fluid. This caused the seals in the piston to swell enough that the piston wouldn't return to the normal position because the springs were not strong enough. Flushing can work out this contamination and possible will let the seals go back to normal.

As for working on it. There is no way to do this without having to bleed the brakes.

I ordered the piston set this spring but they were out of stock so I went with the entire assembly. I have read that the piston set is available now and is about half the cost of the entire assembly.

I should add that I knew I had an issue because I had a hard time pushing the bike around in the parking lot.

 

[SoloTotoCoyote]

Something also..........if the pistons on the rear caliper are not cleaned prior to pressing them back in during a brake pad change, dirt can get between the piston and seal. When you go to brake the dirt prevents the piston from moving properly and can have the brake pad unable to pull back from the rotor. You can fry the rotor and pad pretty quick............ and I'm speaking from experience here with the ST. I destroyed a set of pads and warped the crap out of the rotor this way.

 

[dduelin]

I'm just trying to confirm the SMC is causing my rear brake drag on my 2004 ST1300A.

If I push on the SMC it will stop the rear wheel from spinning but when I release the SMC the rear wheel drags. Likewise, when I press on the rear brake pedal the rear wheel drags. From the research I have done on this site it appears I have a faulty SMC. Does this sound right?

Can the SMC bracket assy be removed from the bike and the piston set be removed & cleaned without going through the brake bleed process? Approximately 10,000 miles ago I followed the instructions in the service manual & documentation on this site to replace my brake pads & brake fluid. But, I was hoping for a short cut to try cleaning the SMC piston.

I have found the following information on this site:
45620-MCS-G03 piston set
06454-MCS-G02 bracket sub-assy
Are these the parts that most folks have used to repair their SMC?

I still have extended warranty coverage on my 04 so I'm hoping Honda will take care of this for me. But if not I wanted to make sure I was on the right track.

Thanks,
tman

If the rear brake drags after manually engaging the SMC by pressing the SMC closed while a helper rotates the rear wheel and the rear brake also drags also using the rear brake pedal then it isn't the SMC, at least not the SMC by itself. The rear brake pedal does not engage the SMC.

Do the pads slide easily on the locating pin? It is possible to force one or both pads far enough into the caliper to get the pin screwed in but the pad(s) are not properly seated in the anti-rattle spring. There is a projection on the forward end of the pads that fits into a corresponding notch in the spring. If they are not loose on the locating pin the pad(s) will not easily retract away from the rotor when the brakes are released.

 

[dduelin]

As for cleaning it. In my case it wasn't a case of anything being dirty. What happened was water worked past the seal, contaminating the fluid. This caused the seals in the piston to swell enough that the piston wouldn't return to the normal position because the springs were not strong enough.

I have a difficult time understanding how this can happen. One, brake fluid is much more slippery than water is. The seals are designed to keep fluid on one side and dirt and/or moisture on the other. Two, the fluid in the system is under high pressure when the brakes are applied. Water on the outside is not under pressure. If the seals are bad enough at some point in time to allow water in from the outside they would be leaking fluid out of the SMC bore when the brakes were applied. With no brake fluid leak the seal is doing it's job.

However, the normal downward tilt of the SMC allows air bubbles to accumulate in the SMC bore. Brake fluid normally attracts minute amounts of water through the lines and fittings. When it gets hot the water separates from the brake fluid and this is the cause of corrosion in master and slave cylinder bores and metal lines since hydraulic brakes have been using hydroscopic fluids. This bike has a SMC that unfortunately holds the accumulated moisture and if maintenance is neglected or not done completely (yes, remove and tilt the caliper when a bleed is done) the corrosion is going to start in or be worse in the SMC. It corrodes from the inside out. This is my thoughts anyway - I could be all wet.

At any rate, it is very important to do the fluid changes on time even if the bike is not ridden very much.

 

[Smallville]

Some brake toughing is normal... is your rear brake dragging to the point it's slowing the bike?

+1. If its just a little rubbing, I think you may be worried about nothing. Especially the way you describe it. I bet your front wheel does the same thing.

 

[sennister]

I have a difficult time understanding how this can happen. One, brake fluid is much more slippery than water is. The seals are designed to keep fluid on one side and dirt and/or moisture on the other. Two, the fluid in the system is under high pressure when the brakes are applied. Water on the outside is not under pressure. If the seals are bad enough at some point in time to allow water in from the outside they would be leaking fluid out of the SMC bore when the brakes were applied. With no brake fluid leak the seal is doing it's job.

However, the normal downward tilt of the SMC allows air bubbles to accumulate in the SMC bore. Brake fluid normally attracts minute amounts of water through the lines and fittings. When it gets hot the water separates from the brake fluid and this is the cause of corrosion in master and slave cylinder bores and metal lines since hydraulic brakes have been using hydroscopic fluids. This bike has a SMC that unfortunately holds the accumulated moisture and if maintenance is neglected or not done completely (yes, remove and tilt the caliper when a bleed is done) the corrosion is going to start in or be worse in the SMC. It corrodes from the inside out. This is my thoughts anyway - I could be all wet.

At any rate, it is very important to do the fluid changes on time even if the bike is not ridden very much.

I am not sure but when I got the piston out of the SMC the fluid was like milk. Now I had about 75K miles on that SMC. There was no mention of changing it in the detailed service logs. The previous owner was meticulous about maint on it and it wasn't due for another flush of the brakes for a while yet. As for corrosion. I have the old assembly sitting on my bench still. I can take some photos of it. There were no signs of corrosion that I could see. The bore of the SMC was very bright and shiny. The piston would not move though. I had a heck of a time trying to get it out. I had to crank up the regulator on my compressor to 120PSI and pulse on/off blowing for about 15 minutes before it finally blew out. There is no way the little spring inside there was able to move the piston. The biggest thing that I noticed was that I had this rattle when hitting bumps because the piston was stuck. When I moved the left caliper, the assembly would flop on the fork and not provide braking power to the rear wheel. Though from time to time I would notice it dragging. For instance I had a hard time backing into a parking lot a couple times even though it was flat.

 

[dduelin]

Mine rattles too and has since the beginning, but it is clean and works as designed at 81,465 miles. I have done all the flushes and trust the mechanic. Maybe the PO got a bad bottle of fluid or took a short cut with the last bleed or three.

 

[sennister]

Mine rattles too and has since the beginning, but it is clean and works as designed at 81,465 miles. I have done all the flushes and trust the mechanic. Maybe the PO got a bad bottle of fluid or took a short cut with the last bleed or three.

While possible, the rest of the fluid that came out of the bike looked perfect. Also the bike is an AZ bike so it didn't see much rain and humidity until I brought it back to MN.

Now that I have replaced the SMC Assembly, the rattle went away.

 

[dduelin]

While possible, the rest of the fluid that came out of the bike looked perfect. Also the bike is an AZ bike so it didn't see much rain and humidity until I brought it back to MN.

Now that I have replaced the SMC Assembly, the rattle went away.

It might come back at about 8000 miles. A bleed at 12000 takes care of it. You detail a mystery at any rate. I live in a very humid climate and ride in the rain quite often. The water stays out and the fluid stays in - so far.

 

[sennister]

It might come back at about 8000 miles. A bleed at 12000 takes care of it. You detail a mystery at any rate. I live in a very humid climate and ride in the rain quite often. The water stays out and the fluid stays in - so far.

Yeah, I have read that the rattle can be cured by bleeding. I tried that but my issue was more significant.

One thing that may have been a contributing factor was that everything was going well until I replaced my rear brake pads. I cleaned the pistons as I normally do then pushed them back in. I got on the bike and I actuated the rear brake pedal to move the piston back to where they should be. I failed the actuate the front SMC to move the pistons back to where the should be. The first time I applied the brakes it would have bottomed out the SMC piston. It never seemed to work right after that. I do know that when doing this initial braking to seat the pads care should be taken to not squeeze the lever too tight. The piston can get overextended into areas of the cylinder where it isn't smooth and this can damage the piston seals. Like I said it could have been a contributing factor. This is my first bike with linked brakes.

 

[tman]

---> +1. If its just a little rubbing, I think you may be worried about nothing. Especially the way you describe it. I bet your front wheel does the same thing.

I realize it is normal for the rear brakes to rub a little, but at times it almost locks the rear wheel. I had the same thing happen before and it went away after replacing the pads & brake fluid. At that time (approx. 10,000 miles ago) I was unaware of the known issue with the SMC so I didn't pull it apart to inspect/clean it. With the pads removed I extended the pistons out as far as they could go and cleaned the exterior.

I am a little disappointed with the brakes on the ST1300. They appear to be a lot higher maintenance than the ST1100. I never had a problem with my ST1100.

tman

 

[Smallville]

The ST1300 does seem to have a complex braking system. Maybe too complex.

It seems to me that if the SMC will operate, it shouldn't be locking up. But perhaps thats not the case. Do you notice the rear brake rotor becoming hot or smelling of hot brakes?

 

[tman]

I haven't ridden my ST1300 much lately. I wanted to take a ride the other day but I noticed the rear brake drag issue during my pre-ride inspection. Looks like I have some work to do before I can take a ride.