SMC Rattle

Tom P

Tom P

Joined
Sep 5, 2006
Messages
148
Location
Vista, CA
Bike
2004 ST1300
STOC #
6453
I am have some clunking/rattling coming from the front. New bike to me but has 76,000 on it. Just tore the front end apart to redo fork fluid and seals. Put everything back
with the proper fasteners and can not figure out what would be rattling...It was there before the fork overhaul. It happens on rapid sharp bumps.

Saw a thread where it was suggested it was the SMC. I can rattle it by hand and wondered if anyone knows how to stop it from rattling. Is this the way they come from the factory?
Don't know if that is what I am hearing. Checked play in the head bearings and as far as I can tell there is no slop and they are smooth.

Any suggestions or wisdom would sure help.:confused:
 
Mine did that as well. The best way to tell if it is the SMC is to apply the front brake when going over a bumpy section where you would hear the rattle. The braking action will compress the SMC and take out the slack that is causing the rattle and it will sound normal.

As for a fix... Well in my case the SMC was bottomed out and stuck. The only fix I had was to buy the rebuild kit. This was a couple years ago when they were on nation wide backorder. So I ended up buying the entire assembly and swapped it out. You can try and take it apart and see if the piston can bee freed but in my case it was a lost cause. My mileage at the time was almost exactly where you were. Right around 75K at the time.
 
Igofar and I took one of those apart and both of us agreed that the next time we would just buy a replacement. It isn't hard to take apart with the right tools... but it's a hassle. Be careful putting it back together. You have to make sure the sealed in bearings on the fork ( I think ) don't have any loctite in them and that they are well lubed. Loctite the threads on the fork and not the threads on the bolt when putting it back together. There is also a fiber bushing in there that you don't want to crush. You can't just buy the bushing.
 
My SMC rattled a bit... Easy fix for me was to properly bleed the system (tilting the smc).
After the full bleed, I had no rattle at all...but I have heard that some times it comes back.
Anyway, a bleed is a simple cheap possible fix before pullin it apart.

Side note: test the smc for function by manually applying while spinning the rear tire
 
...the death rattle....this happens when the SMC rod is corroded and pitted, causing the piston to stick or drag in the cylinder.
Bleeding the system will appear to quiet the noise down some, but it is only hiding the fact that your SMC has died and is no longer working.
Replace the SMC as an entire unit, then flush and do a proper bleed.
You got more miles than most on your SMC. I've replaced them with as little at 17K miles on them.
Being exposed (facing forward) to the road salt, water, dirt, etc. can kill them quick if you don't keep them clean and dry.
.02
 
There is natural play in two areas of the SMC/left front caliper assembly and neither is indicative of a need to replace anything although close inspection is required to make sure wear is not out of limits. The first is where the clevis joint passes the pushrod through a close-fitting washer at the forward opening of the SMC bore. There is play or clearance here even in a brand new clevis pushrod and the washer can rattle on the rod. The SMC on my bike is perfectly functional at 111,xxx miles and I get a bit of rattle here. The other is in the lower pivot bearing. The needle bearing is a slip fit into the SMC bracket and you can grab the SMC and feel a small amount of play in the transverse axis of the bracket to the lower fork leg. Honda does not give a service limit to this side-to-side movement so common sense is required. If the needle bearing is clean and free a small amount of transverse play is OK as long as the play is not axial indicating the bearing is worn.

Corrosion and pitting in the SMC bore is entirely separate from the areas I mentioned. If the SMC is frozen it needs to be replaced, if it is sticking or dragging and cannot be repaired that is entirely separate from noise or rattle at other wear points. You could rebuild the SMC and still have noise.
 
Such good information...I love this forum! Thank you all. I will do some sleuthing this week and see what I find and report back. Hopefully it is this, if not :confused:
 
Tom P said:
Such good information...I love this forum! Thank you all. I will do some sleuthing this week and see what I find and report back. Hopefully it is this, if not :confused:
Click to expand...
I'll add I was sleuthing this same noise last week. I replaced the steering head bearings about 15k ago and while I had some rattle from the brake bracket for what seems like forever I began to worry the head bearings had loosened up to the point of making noise when going over a bumps or bad pavement. In my case the head bearings were not loose and the noise was just the same noise I had had for years . Now it just does not go away with a bleed like it used to. Already in my spares bin are the parts to replace the clevis pushrod assembly and today I intend to order a new pivot bearing ( the "collar" part #45442 MAT 000).

Edit update... I went to the dealer today and found the collar is just the inner race of the pivot bearing. The bearing is not shown in the left front brake caliper fiche but rather in the front fork fiche. While I was at it I ordered the needle bearing and seals. Back at home I can take one hand to steady the front wheel and the other to move the SMC back and forth and forward and backward in order to seek out the rattle noise. In my bike the rattle is coming from the clevis pushrod assembly but at the mileage over 110,000 now I am just going to replace all the moving and/or wear parts although the linked brakes are working fine.

I am not sure the comment was directed at me but I ride my bike year round in all kinds of weather. I don't think riding in rain has anything to do with SMC innards going bad but I think neglecting recommended fluid replacement maintenance has everything to do with it. This is a complicated braking system and neglecting regular fluid replacement and improper bleeding doesn't invite problems - it guarantees them when the miles and years add up.
 
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I would imagine that the type of rider you are will impact the life of this. If you are a fair weather rider, odds are that you won't have an issue for many many miles. Personally I ride rain or shine so to help combat this issue I flush my brakes every year rather than every 2 years as called for. Also I think my issue was partly caused by replacing the brakes on the rear caliper. While I pumped the brake to push the caliper piston into position I didn't pump the SMC. So the first time I hit the front brakes the SMC would have bottomed out as there was little to no resistance (as the piston wouldn't have been touching the pad). The piston then was stuck at the bottom of the cylinder. Since that learning experience I now carefully pump the SMC until pressure is restored and it is functioning normally with the bike on the lift before taking it out for a ride.

If you do dig into the SMC I know I had a devil of a time trying to blow it out with compressed air because it was stuck so bad. I was working on it for 45 minutes or so with 100PSI air before I finally got it out. The brake fluid in this area was contaminated and looked like milk. It is possible that the contaminated fluid caused the seal in the piston to swell and that was part of the problem. Once I got it out and cleaned up I discovered that it wouldn't move freely in the cylinder even though it wasn't pitted. For me the rebuild kit would have been an option but the kit was on backorder. I think the rebuild kit was around $50 and the entire assembly $120. The assembly was available at the time. If I drive my truck to work for a week vs riding the bike the difference in fuel cost at the time was $80 so it was a wash to get the entire assembly rather than gamble that the rebuild kit would be on backorder for less than a week.

The biggest lesson I learned was that I have to remember to pump the front left caliper when working on the rear brakes or wheel just like you want to do with the foot brake. It is also a good idea not to move it to the limits when pumping. The same goes for cages. I usually put a block of wood under the brake so you don't go to the floor. If you do you can get into areas of the cylinder that are not as smooth as the seals don't normally ride in that area. This can damage the seals in the master cylinder and you will have to replace them. So I pump only using about 1/2 the movable range. Takes a minute longer but prevents issues.
 
sennister said:
The biggest lesson I learned was that I have to remember to pump the front left caliper when working on the rear brakes or wheel just like you want to do with the foot brake. It is also a good idea not to move it to the limits when pumping. The same goes for cages. I usually put a block of wood under the brake so you don't go to the floor. If you do you can get into areas of the cylinder that are not as smooth as the seals don't normally ride in that area. This can damage the seals in the master cylinder and you will have to replace them. So I pump only using about 1/2 the movable range. Takes a minute longer but prevents issues.
Click to expand...

Not sure I understand what you mean when you say "remember to pump the front left caliper when working on the rear brakes or wheel just like you want to do with the foot brake." How do you pump the left front caliper? Do mean to pump the front brakes with the brake handle or pump the SMC via the back brake pedal? I am not familiar with the ST1300 brake system, though I am learning fast. I also assume you also mean that we are bleeding it and inclining it to 15 degrees?
Oh and I also saw the whole unit at Powersports Plus for $94.99 plus $9.39 shipping. I'll go that way if mine is toast.
 
Tom P said:
Not sure I understand what you mean when you say "remember to pump the front left caliper when working on the rear brakes or wheel just like you want to do with the foot brake." How do you pump the left front caliper? Do mean to pump the front brakes with the brake handle or pump the SMC via the back brake pedal? I am not familiar with the ST1300 brake system, though I am learning fast. I also assume you also mean that we are bleeding it and inclining it to 15 degrees?
Oh and I also saw the whole unit at Powersports Plus for $94.99 plus $9.39 shipping. I'll go that way if mine is toast.
Click to expand...

The reason for the SMC is to provide braking pressure to the rear caliper when the front brakes are applied. When the bike is in motion and the front brakes applied the braking action will cause upward pressure on the calipers. The right caliper is hard mounted to the fork but the left caliper is designed with the SMC at the upper mounting location. This upward pressure compresses the SMC. This movement of the piston in the SMC sends brake fluid to the rear caliper.

Ok going from memory here as I don't have the drawing in front of me....

Each caliper on the bike has 3 pistons. The outer two pistons are operated by the front brake lever. The SMC then acts like a booster to push more fluid back to the outer to pistons on the rear caliper. This is how the brakes are linked in reference to the front brake lever. As for the rear brake lever. When you press on that the brake fluid is pushed to the proportioning valve on the right frame rail near the coil. This divides up the brake fluid sending some to the middle piston on the front calipers and the middle piston on the rear caliper.

So when you change brake pads you need to clean the pistons and push them back into the caliper so that you have enough clearance to slip them over the rotors. Odds are you will push them in too far which isn't a big deal as you can pump the brakes a couple times and it will push out the pistons. This is fine for the foot brake because the fluid is sent to the center pistons via the proportioning valve. A couple quick pumps will move the pistons to the proper position. As for the front brake lever if you pump that you will only move the outer pistons on the front calipers to the proper position as the bike is stationary and the SMC will not be activated. The two outer pistons will remain compressed into the rear caliper until you go out for a ride and hit your front brakes. You can manually cycle the SMC a few times by pressing on the back part of the left front caliper a couple times. You will see how the caliper is designed to rotate and compress the SMC. Every time you do this it will send brake fluid back to the rear caliper and move the pistons out a little more to get them in the proper position. With a properly functioning SMC you will feel it go from being really easy to push the caliper to getting firm in the same manner that the brake lever and pedal stiffens up when pumping them after a brake change.

Does that help?

I will see if I can find the drawing that has been posted here as it helps to see how things are plumbed. Also under the ST1300 service section there are directions on how to bleed the brakes. There is a specific order that they have to be done in.
 
Sennister....YOU ROCK! What a great description. I always wanted to understand what is meant by a "Linked" brake system and you explained it most admirably. I will use this info to diagnose the SMC.
And Tom I like the color diagram. Makes for easier reading by an old fart.
 
Tom P said:
Sennister....YOU ROCK! What a great description. I always wanted to understand what is meant by a "Linked" brake system and you explained it most admirably. I will use this info to diagnose the SMC.
And Tom I like the color diagram. Makes for easier reading by an old fart.
Click to expand...

No problem. Linked brakes is a common term used and basically describes that the bike has brakes kind of like a car. Where when you apply the brakes, braking pressure is applied to both front and rear wheels. Now keep in mind that this is how it works on the ST and every bike with linked brakes execute it in their own way. For instance some bikes have linked brakes for the front brake lever but the rear foot brake only actuates the rear caliper. Just a matter of how they execute it.

One thing that I like about my old 1100 is that the non-ABS 1100s don't have linked brakes. This makes them simple. When I was ready to get a 1300 when I discovered that both the ABS and non-ABS models have linked brakes I knew I wanted an ABS bike. I was going to have to deal with the mess of brake lines going all over the place no matter if I got ABS or not. With the amount of cold weather riding and rain I ride in I figured ABS would be a good thing. I have activated it a couple times.

Good luck with diagnosing the SMC. Like I said mine died around the same mileage. The entire assembly is an easy way to do the replacement. Once you pull the assembly the caliper will slide off the pins on the old assembly. If I recall there are rubber boots that you use a small screwdriver to pop up a bit and the caliper will slide right off and back onto the new assembly. It will take a bit to bleed it out but that process will be the same if you do the assembly or the rebuild kit. So no difference there. Just follow the steps in the ST1300 service section and make sure you don't suck all the brake fluid out of the master cylinder in the process.
 
Yeah , I will "bleed the whole bloody system":eek:: if I get that far. Probably do it good with the miles it has on it.
 
Tom P said:
Pardon my ignorance on this . Why would this be necessary. Would there be a symptom that would be evident if the are out of adjustment?
Click to expand...

Like the saying goes. The only bad question is the one not asked. We don't mind.

Yeah, not saying it needs to be done but the two symptoms depend on which way it is out of whack. Too loose then you get a gravely rattle to the engine. Too tight and there is more of a high pitch squeal. Now the whine of the engine is normal so it is hard to describe until you do the adjustment and see what. With properly adjusted counter balancers the engine is smoother. I know when I did the TB sync and counter balancer adjustment at the same time I went to a smooth bike to one that I thought stalled every time I came to a stop sign or light. It was that much smoother. I think my counter balancer can be tweaked again as I have a little vibration at idle but not bad enough to mess with it. Since you are new you will likely not notice one way or another. That is why I mentioned it in the thread where someone said that they have the plastic off anyhow so what should I do for maint as long as it is off. It won't hurt anything that I am aware of if they are off. It is just a comfort thing.
 
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