Secondary Master Cylinder - FAILURE!

[uptoblackwood]

Thanks, Joe. I'll take a look later.

 

[Coop]

I'm glad you didn't wind up with a plastic needed story!!

 

[ChucksKLRST]

Here is what the internals of the SMC look like. The boot was destroyed in the making of these pictures. What happens is the rubber seals on the right plunger with the spring, swell up and get corrosion embedded in them and then stick.

 

[uptoblackwood]

Great photos, Chuck. Thanks. It shows the rotating ball for the articlulation. I knew there was some kind of join. Funny that the issue has nothing to do with the plunger...well, unless it's the corrosion is a result of water leaking around the top seal???

 

[uptoblackwood]

Me too, Coop!!

 

[ChucksKLRST]

Great photos, Chuck. Thanks. It shows the rotating ball for the articlulation. I knew there was some kind of join. Funny that the issue has nothing to do with the plunger...well, unless it's the corrosion is a result of water leaking around the top seal???

I also belive the spring gets weak, although I can't prove that.

 

[970mike]

I have yet to have a problem with the SMC but I went out and pulled the rubber boot back and shot it full of PB Blaster. Hopefully if any moisture was trapped in there it will displace it.

 

[dduelin]

Great photos, Chuck. Thanks. It shows the rotating ball for the articlulation. I knew there was some kind of join. Funny that the issue has nothing to do with the plunger...well, unless it's the corrosion is a result of water leaking around the top seal???

If the seals are not leaking brake fluid it is unlikely water is leaking in past the seals under atmospheric pressure. Pack the boot with grease if it makes you feel better however the downward tilt of the SMC with outlet holes at its lower end coupled with the heat from the attached caliper is going to concentrate moisture & air in the SMC bore with no way for it to get out until the flushes are carefully done by the book. I believe it is the combination of air and moisture left in the bore that creates the conditions for corrosion to happen.

 

[RCS]

Dave...I am very good about changing fluids and always do them at or before scheduled in the manual. I had just flushed both clutch and brakes about 5,000 miles before this happened.

Glad this event worked out and no one was injured.

When you say you flushed the brakes, did you follow the manual and completely drain the entire system before putting in new fluid per the Service Manual?

 

[thunderfootblue]

Excellent thread--great info!

 

[uptoblackwood]

Dave and Bob....I ALWAYS flush the systems "by the book"....and I'm careful and precise when I do the job.....

 

[uptoblackwood]

Ok...Ted called about the SMC part. Honda does have a new part specificly to replace the SMCs older than the update.....so Joe, we use the old caliper.
Second....I talked to Ted about the corrosion issue and here's what he and Honda say: Looking at Chuck's images, you'll see two flange seals on the internal piston....the bottom seal (to the right on Chuck's photo) and the top seal (to the left on Chuck's photo). The bottom seal's job is to keep the brake hydraulic circuit sealed and pressurized. The top seal works to keep moisture and dirt out of the system. There are two additional sealing mechanisims, both at the top end (connecting rod) to keep water and dirt out.......1. the external boot 2. a flat washer like seal under the retainer clip. All three defenses against water and dirt....eventually fail. The corrosion occurs at the TOP inside cylinder seal area.....and has nothing to do with the inside (bottom) seal keeping the brake's hydraulic system from leaking. Honda added the slot/trough in the new SMC as a 4th defense against the water/dirt problem.

Thanks for those photos, Chuck. Things made a lot of sense after talking to both Ted and the American Honda regional rep about this stuff.

 

[dduelin]

Ok...Ted called about the SMC part. Honda does have a new part specificly to replace the SMCs older than the update.....so Joe, we use the old caliper.
Second....I talked to Ted about the corrosion issue and here's what he and Honda say: Looking at Chuck's images, you'll see two flange seals on the internal piston....the bottom seal (to the right on Chuck's photo) and the top seal (to the left on Chuck's photo). The bottom seal's job is to keep the brake hydraulic circuit sealed and pressurized. The top seal works to keep moisture and dirt out of the system. There are two additional sealing mechanisims, both at the top end (connecting rod) to keep water and dirt out.......1. the external boot 2. a seal under the retainer clip. All three defenses against water and dirt....eventually fail. The corrosion occurs at the TOP inside cylinder seal area.....and has nothing to do with the inside (bottom) seal keeping the brake's hydraulic system from leaking. Honda added the slot/trough in the new SMC as a 4th defense against the water/dirt problem.

Thanks for those photos, Chuck. Things made a lot of sense after talking to both Ted and the American Honda regional rep about this stuff.

Very good information. I know you ride alot and this bike isn't a garage queen. How many miles on the bike?

 

[uptoblackwood]

This is my second ST1300, Dave. I've got about 66000 on this one....(I had about the same mileage on the first).

 

[okmurdog]

Forest, that was bad...glad it wasn't worse!

Thanks for the info - your thread joins a list of similar problems experienced by several people. I've seen this same problem on a local ST in the past (not mine). Normally, stomping on the rear brake --while stopped-- will temporarily release the SMC (push the plunger back out)...at least until the next braking action occurs while the bike is moving.

 

[MidLife]

What I fail to grasp here is why this factually well documented dangerous failure is not recall material?

Honda keeps tweaking the design, thus acknowledging the deficiency. And they are not implementing the SMC scheme in newer bikes either, another sign that they recognize the limits of the design.

Toyota got dinged for imaginary defects. Here we have a string of well proven SMC failures that has exposed a few our riders to life threatening situations. What will it take for Honda to get serious about a final solution to the matter for all of us?

One of us not being as lucky as Forest?

Are we guilty of not having reported all these failures over the years to the NHTSA/ODI (me included!)?

Forest, that was bad...glad it wasn't worse!

Thanks for the info - your thread joins a list of similar problems experienced by several people. I've seen this same problem on a local ST in the past (not mine). Normally, stomping on the rear brake --while stopped-- will temporarily release the SMC (push the plunger back out)...at least until the next braking action occurs while the bike is moving.

I've looked at the brake schematics and always wondered if this rear brake stomping would work to push the piston back. Have you tried it yourself or seen it work? That could be a very useful tip.

Then we'd have to figure out how to disable the rear brake. We would still have the four pistons on the front to get us limping home. Bleeding off the line to the rear caliper would work but is messy on the road.

Maybe there is a part on the SMC actuator that could be removed so the SMC piston is no longer compressed while braking?

 

[RCS]

Dave and Bob....I ALWAYS flush the systems "by the book"....and I'm careful and precise when I do the job.....

Thank you for the information. Good to know. I will now purchase a new secondary master cylinder for the Bin-o-parts box.

 

[Mellow]

Then we'd have to figure out how to disable the rear brake. We would still have the four pistons on the front to get us limping home. Bleeding off the line to the rear caliper would work but is messy on the road.

Yeah, bleeding off the rear brake would get you home but in the process probably mess up your wheels and any paint and also might get on the tire and make things just as bad/slippery. Another option would be to put something between the smc and fork to block it's movement but that seems a bit dangerous as well.

I agree that it's strange there was a 2008+ recall on the rear brake res hose with a very few documented issues when there are many, just here, of the smc failures. That's assuming the 2008 change in the smc was a real fix...

 

[ChucksKLRST]

I've looked at the brake schematics and always wondered if this rear brake stomping would work to push the piston back. Have you tried it yourself or seen it work? That could be a very useful tip.

Yes it does work in some cases. My SMC was draging for a long time and then finally got to a point I was going thru rear pads in about 10 to 16 k miles. Normal was about 25k miles for me. Just before I rebuilt the SMC I could feel it dragging and a good stomp on the rear brake peddle would free it up until the next time it was engaged. I rebuild the SMC at about 80k miles, and now all is well.

 

[Tom Mac 04a]

Maybe there is a part on the SMC actuator that could be removed so the SMC piston is no longer compressed while braking?

That would be nice and easy... course you could just cut the mounting connector off