Waterproofing the SMC

I am toying around with some ideas to waterproof the SMC.

I used my old SMC for testing.

"100% Silicone Sealant can withstand extreme temperature conditions."

Any thoughts?





After talking to Larry (Igofar), who's opinion I respect on these matters, there is always a potential/risk to trap moisture while at the same time trying to keep it out.

Do it if it makes you feel better but regular service according to the owners manual is more important and all that is necessary. Mine still works as designed for 10 years now and 162,xxx miles.

dduelin said:

Do it if it makes you feel better but regular service according to the owners manual is more important and all that is necessary. Mine still works as designed for 10 years now and 162,xxx miles.

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I am not sure regular flushing will prevent water from corroding the cylinder bore or the push rod, which is what I ended up having. In fact water should never come into contact with the brake fluid from the SMC. All the corrosion I had was on top where the push rod made contact with the bore.
Now I am thinking how to keep the water from getting in there in the first place.
With all the SMC failures written about here I think there is more to it than regular flushing of the brake fluid. JMO.

Keep the drain open. Water in, water out.

dduelin said:

Keep the drain open. Water in, water out.

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Are you talking about the tiny weep hole at the base of the plunger?

It is not effective or there would not be so many SMC failures due to corrosion.

ST-Traveler said:

After talking to Larry (Igofar), who's opinion I respect on these matters, there is always a potential/risk to trap moisture while at the same time trying to keep it out.

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You can reduce the chance of trapping moisture by warming up any assembly with a hair dryer prior to sealing. Hair dryer, not heat gun as plastic and vinyl can be melted if the temperature is overdone.

I would think the silicone added to the plunger would restrict the movement somewhat and diminish the effectiveness of the SMC.

vinny said:

I would think the silicone added to the plunger would restrict the movement somewhat and diminish the effectiveness of the SMC.

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Hey Vinny,
I tested it on my old SMC and it does not effect the movement of the SMC push rod at all, There is only 1-2mm of movement after the bleed process. The silicone is flexible enough that I don't see that as a problem. But it is something I considered as a possibility.

Oldbikefixr said:

You can reduce the chance of trapping moisture by warming up any assembly with a hair dryer prior to sealing. Hair dryer, not heat gun as plastic and vinyl can be melted if the temperature is overdone.

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What I was thinking of is the moisture from condensation type issues not from the original sealing of the boot. I think once the area is dry and then sealed the only potential with moisture would be from hot to cold condensation under the boot that would not be able to escape.

In the service manual on page 17-24 it says to apply silicone grease to the push rod tip and piston contact point as well as the boot fitting area.

ST-Traveler said:

What I was thinking of is the moisture from condensation type issues not from the original sealing of the boot. I think once the area is dry and then sealed the only potential with moisture would be from hot to cold condensation under the boot that would not be able to escape.

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If the unit is properly dehumidified there will be no moisture inside the unit to condense out. If the unit can still pass atmosphere(breathe), attempting to seal it further than Mr Honda's folks designed may be pointless.

To be certain there are many SMC failures but there are 10 years of bikes in service and there are many that have had no problems. Of those with problems we generally do not have a complete service history. Unless we have access to benchmark data concerning failure rates and reasons all we are doing here is SWAGing.

Give sealing it up a try and see what happens.

dduelin said:

To be certain there are many SMC failures but there are 10 years of bikes in service and there are many that have had no problems. Of those with problems we generally do not have a complete service history. Unless we have access to benchmark data concerning failure rates and reasons all we are doing here is SWAGing.

Give sealing it up a try and see what happens.

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True but something to consider is the fact that probably only a handful of those bikes have over 100,000 miles and there has been reports I have read with as little as 32,000 miles until failure.
Plus for a discussion point, I think there are many more failures that may or may not be reported here on the forum. They are partially failing but the owners don't realize it because they simply do not ride them enough to tell or even notice it due to the intermittent nature of the failures.

7 yrs. / 117K on my 1300 & NO probs. w/SMC. I never spray any pressure washers near that area, and try to keep it as dry as possible.
Also, about twice a year, put a small shot of light oil on the assy.

Hi John, sorry to open this thread again but I am having to have a look at my SMC as l do not think that its working correctly. When l turn the rear wheel l have tried to manually move the left caliper or SMC, nothing happens. To be honest not sure if l am doing this quite right, any photos out there? l have downloaded your guide to avoiding the pit fulls on brakes, excellent document by the way and all the various threads on this matter. Anyway a question about the water proofing item, in your guide and the SM it mentions using red rubber grease but in most threads mentions silicone grease. Whats best or are they both good? Not sure whether to attempt to strip the SMC first as l need the bike for work, guess I'm just building up the courage as the bleeding also sounds like fun,,, not.

The photo I put up in an earlier smc thread showed the relatively dry build up of gunk at the piston/pushrod contact points inside my smc. It seemed to be a build up of road dirt and brake pad dust,, which became caked from many water wettings. While I waited for my new smc to arrive, I decided to clean up the old smc right in the bike. I only removed the bolts mounting the left caliper line to it's fork, and did not undo any of the hydraulics. Disassembly and clean up was not too difficult. I reassembled it with a liberal amount of high-temp synthetic silicone brake grease, between the boot and the piston top. When all back together, it seems to work as well as it did prior to my rear brake seizure. I do think the grease will prevent the build up of crud,,, and I will likely drive it for a while to assess how the contaminates are able to enter past the boot,, before I eventually install the new smc. Using the manual test method described above, the smc operates the same as it always had before the lock up. Cat'

I just clean out the rubber boot with a Q-tip or whatever I can get in there without causing damage and squirt some silicone grease in there about every front tire change. I also grease the plain and roller bearings at the upper and lower caliper mounts with waterproof lithium grease at the same time. Never any SMC issues, 13 years, 99k miles.

Never had any SMC issues in 11 years 167,000 miles. I change the fluid on schedule and peek under the SMC boot now and then. I don't grease it [boot] just keep the drain clean and open. I did replace the lower caliper needle bearing something after 100,000. The collar seized on the pivot bolt although the bearing itself was still good.

So much great info and advice, I have already worked on the front brakes last weekend and will sort out the rear calliper this weekend. It has been quite interesting as after my usual 40 mile commute to work, checking the temp of all the callipers noted that they were all cool to touch (not raining) but the front right was just very slightly warmer. Anyway rear brakes this weekend definitely going to have a peek at the SMC, like the suggestion of the Q tip and will bleed the system as per recommendations. Fingers crossed.

Hi, bleed the system as per recommendations but now have noticed that with the bike on the centre stand turn the rear wheel by hand apply the rear brake, the wheel stops but stays on for a second or two before releasing. I assume that there is possibly air still in the system, driving me nuts.