SMC Rebuild Master Piston Removal

Gug

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I am in the middle of this and the Master piston is corroded to the point of "How do you remove it"??? Any ideas and still salvage the assembly? Also what should I clean out the bore with?
 
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Soak it in your favourite penetrating oil, preferably overnight, then use a vice grip needle nose pliers to try to rotate it and move it in and out. You may have to move it many times to remove the corrosion to make a smooth path so it can pop out. Keep spraying penetrating oil In the bore to flush out the gunk while you are trying to remove it.

Also check this active out for tips also.
https://www.st-owners.com/forums/showthread.php?133460-ST1300-Secondary-Master-Cylinder-Rebuild-SMC

Best of Luck
 
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Byron

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If you can find it locally see if you can locate some Kroil. Good penetrator, will actually soak into the metal and loosen corrosion.
 
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Gug

Gug

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Well I believe the SMC Bracket Assembly is shot. It was so corroded in there that you couldn't even tell where the Master Piston was in contrast to the outside diameter of the housing, it was froze level to the top of the bore. I should have taken detailed pictures of this.

After 4 hours of penetrating oil, tapping with a brass hammer, a bit of heat (not to much) the piston moved maybe a 1/4". But the top end of the bore is not shiny aluminum, it is a dull blackish color that indicates a fine corrosion. So it appears an entire bracket sub assembly is in order.

I hesitate to remove a piston that is that corroded and replace with a clean one in MY braking system. The tolerances are to much of a concern to do that. So why didn't Honda recall the ST's on this issue, they recalled the Gold Wings. Although I spoke to a Gold Wing friend yesterday and he said they "Inspected it" and sent him on his way stating there was no problem. Knowing what I know now they should have at the very least filled that top boot with silicone grease otherwise in the future this will be an issue for him as well.
 

Byron

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When this topic was first aired, I believe Honda's fix was to put a hole into the housing on the downhill side so water could drain instead of be trapped on top.
 
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146K and I haven't touched my SMC. How unusual is this? I do think I will swap it out over the winter for piece of mind.
 
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Gug

Gug

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146K and I haven't touched my SMC. How unusual is this? I do think I will swap it out over the winter for piece of mind.
Knowing what I know now, I would lift the boot on top, take a look in there for any corrosion, if there is replace the piston set (45620-MCS-G04 is the new part). If there isn't any corrosion put silicon grease in there and put it on your maintenance schedule to perform this at least annually.

From the design of this item it is unfortunate but there are those that are gone and those that are going to go. The silicon grease maintenance is critical to longevity here.
 

mlheck

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I replaced mine on a '05 garage kept bike this spring and it looked as good as new. Nice and shiny. So I wonder why some are corroding so bad and others aren't. I never power wash my bike, and I do ride in rain.
 
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Gug

Gug

Joined
Mar 6, 2005
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Trenton, MI.
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18' Goldwing Tour
I replaced mine on a '05 garage kept bike this spring and it looked as good as new. Nice and shiny. So I wonder why some are corroding so bad and others aren't. I never power wash my bike, and I do ride in rain.
Good question. I have ridden thousands of miles in the rain. Could that be it? I am sure there are some temp changes occurring in the SMC, producing moisture that is trapped underneath the cover. I would think it is all of the above.
 

dduelin

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I replaced mine on a '05 garage kept bike this spring and it looked as good as new. Nice and shiny. So I wonder why some are corroding so bad and others aren't. I never power wash my bike, and I do ride in rain.
^^^^ This. With my high mileage '05 I am a prime candidate for repair but mine works like new and when I do the 12k brake fluid flush & replacement it always looks good under the boot. I ride in rain all the time and wash my bike OCD after almost every ride and live in a humid sub tropical climate. Mine has all the opportunity to go bad yet....

The early bikes (2003-2007????) have a drain hole situated at the bottom of the upturned open bore where it should drain OK but it is a small hole and could be blocked by debris. I wonder if one is unlucky enough to have the drain clog then that is the beginning of the corrosion. I've never greased mine under the thought that then it would attract dust/ grime under the boot but rather leave it dry where water can drain and evaporate.
 
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