Article [13] ST1300 - Secondary Master Cylinder Rebuild- SMC

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Secondary Master Cylinder Rebuild- SMC

This is a job that probably all ST1300's over 5 years old need to consider. A regular addition of silicon grease into the outer boot might be excellent preventive maintenance. Forest had warned me of this problem but I really didn't understand the problem until Lynne's rear brake began locking up, enough to damage the rear disc and toast the rear piston seals. With a more thorough research of this site I was able to understand the problem. This really helped as I was able to direct the service manager as to the real problem when we took her bike in for repair under the extended warranty. The repair took three weeks but was finally completed. I felt that I needed to get mine done before my ST had similar results. I would recommend doing this job when you are replacing all the brake fluid.

Here is the front left brake caliper removed, the SMC is on the top. The push rod is on top with the bolt partly reinserted.



The manual recommends removing the entire left front caliper to work on it but I thought I might be able to rebuild it in place and avoid draining all the brake fluid. Good idea but I was not able to get the snap ring out so I took the caliper off. You will need to loosen the brake hose oil bolts before removing the caliper from the attachments to the wheel as they can be very tight.






After removing the caliper I completed removal of all the oil bolts and let the brake fluid drain into a container on the floor.




So now just to pull the boot back and take out the snap ring... It was really stuck so using a vise grip on the eye end and a 10mm wrench under the boot I just took apart the push rod assembly. Now I had direct access to the snap ring, it was still hard to remove. A good, high quality snap ring tool would be a good investment.



Now the push rod and the master piston could be removed. Note the crude and corrosion.




Cleaning out the cylinder would be hard while still attached to the brake lines

Here are the new parts and tools you will need. All the parts come in the piston set 45620-MCS-G03



Soaking the master piston and seal in brake fluid is good before installation. I also found it necessary to take apart the new push rod assembly to get the
push rod and snap ring in place, it was fairly tight.



The boot and eyelet end are easy to replace after the push rod is in place.
I put lots of silicon grease under the boot.



Now you are ready to reattach the brake lines and brake caliper. I then refilled and bled all the brake lines per the standard sequence. It did take some time to get all the air out, I did it twice. Always a circus to go through that complex sequence....
 
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Mellow

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Nice! You're on fire today.
 
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Scooter

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How was the condition of the cylinder bore and was is difficult to clean? Do you recall how many copper crush washers there were on all of the front hoses going to that left caliper? Did you replace those or just reuse them. (One of my pet peeves is the price they charge for a simple copper washer).

Last question to anyone out there: Where can you find a good, sturdy snap ring tool? Harbor Freights unit is not very robust and really cannot handle large tasks.

Nice pictures BTW...
 
OP
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Cylinder was in good shape, just brush and rinsed out.
A washer on both sides of the eye hose connector.
I reused the old washers.
Not sure on the source for the snap ring pliers.
 
OP
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Here are some additional comments and pictures of the newer Honda OEM replacement parts for this repair from Igofar.

I will now attempt to attach a couple photos of the new and old parts.
The old style (I believe up to 08' or 09') is once piece, has a thicker spring, a metal to metal contact surface etc.
The newer design attached the contact pad to the spring only, allowing more flex and smoother operation and movement, the spring is also smaller dia. and moves in the bore easier.
DISCLAIMER these parts are listed by year on the parts list, and they still may be selling the old style for prior years, this I don't know for sure, I did measure the bore, SMC housing, caliper, etc. and it APPEARS to be a direct drop in replacement part. Do this at your own risk...I'm now finished with the disclaimer LOL.
Anyway, thought it may help other folks with SMC issues. I also posted a thread about this on the forum, but don't know where to look to find it again.

Igofar.





 
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I noticed that the SM cautions against disassembling the SMC push rod or "the correct brake performance will not be obtained". A photo in the SM shows the snap ring being removed with the boot apparently just "peeled back" to gain access to the snap ring, though I can't tell for certain if that's the case. Jeff, or anyone else who has serviced the SMC, did you see any particular reason why the SM includes this caution?
 

dduelin

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The pushrod has to be a precise length to operate the SMC properly. It is threaded together and could be assembled too short or too long hence the warning. If you carefully measure the length of exposed threads prior to disassembly it would be reassembled to the correct length and all is good again.
 

v8-7

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As I stated in my post on this subject, I measured my bad piston ( no corrosion)
at 13.96-14.25mm ( before I shaved it) .

The replacement piston ( old style ) that I borrowed measured 13.96-14.20mm.

The new unused piston, that did not arrive in time for me to install before my trip, measures 13.95-13.96mm.


You can see in the last picture of the thread I posted ( https://www.st-owners.com/forums/showthread.php?132690-Another-SMC-repair&highlight= )

that after I turned the old piston down, on the left side of the piston, it is still dark.

so I did not take any material off from the smaller part of the diameter. , so the measurement is still minimum 13.96.


(I should have measured it before re-installing it so I could document this, but I only know it moved easily in the test fit ).

My "shaved " piston is therefore 13.96 - <14.20
The new piston being 13.95- 13.96.

I can't envision what could cause the piston to mushroom in size so I can only guess that the manufacturing tolerances were bad .
This is somewhat verified by the measurement of the new , borrowed , piston being significantly out of round and the new redesigned piston measuring
13.95-13.96 a much improved tolerance .

If you have a chance, go ahead and measure any of the pistons you come across and let me know your findings .
 
OP
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Talking with some Suzuki GXR owners the other day I found out the large recall on the Suzuki brakes was because of piston problems. Some were incorrectly manufactured, not round etc... Sound familiar. I bet Honda and Suzuki get their brake pistons from the same place...
 

mlheck

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So what is the part number for the new style SMC?

Sent from my XT907 using Tapatalk
 

mlheck

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My bad. I missed it the first time I read the how to.

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ben

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I recently tore my secondary master cylinder apart due to the rear brake sticking. When I got the snap ring off and the push rod out, I found the top surface of the master piston and interior of the cylinder loaded with corrosion. The corroded particles were effectively seizing the piston in the compressed position. I then cleaned the piston and push rod with fine grained sand paper, being careful not to touch the rubber seal, and cleaned the interior of the cylinder with shop towels. Just to try it, I inserted the old piston back into the cylinder and it seemed to compress and rebound freely. So, I proceeded to re-assemble the SMC with all the original parts and it's worked fine for the last 200 miles. Does anyone have any thoughts on this method of not using replacement parts/rebuild kit? I understand that the corrosion has an increased likelihood to occur again sooner with the old parts rather than with new ones.

On another note, this was my first time tearing apart my ST and all the useful information on this forum was extremely helpful for me for everything from the SMC to tupperware removal and brake bleeding. Thanks to all for all your input.
 
OP
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Your fix should work for sometime. I would put some silicon grease on top of the piston inside the boot to keep this area as dry as possible....
 

Scooter

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Your fix should work for sometime. I would put some silicon grease on top of the piston inside the boot to keep this area as dry as possible....
+1 The important thing is to make sure water doesn't get into there again to cause another round of corrosion. I'm not sure what the advantages of putting a new part in there is if you've done a good job of cleaning up the original assembly and it moves freely...
 

mlheck

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Took the SMC apart on my '05 with 50,000 miles on it today and was pleasantly surprised by what I found.


Clean as a whistle. I had a new style plunger to but back in. Now to bleed out the air.
 
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