Intermittant RR brake drag

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Sorry Don B. , RR is short for rear. The rear brake will lock onto the rear rotor pretty substantially when the brake pedal is applied. I can manually break it free ( so to speek) by manually cycling the SMC. I am hoping this will repair the issue but it is possible that the PCV may also be part of the problem. I am trying to post as much diagnostic info as I can in this thread so as to help out the next ST-Owner that may experience the same issue if not now but in the future.

The inner pad on the rear rotor drags because I can see it move when I rotate the tire, where the inner pad does not move at all.

On a side note - how much silicone grease do you all put in the caliper bracket slides? do you pack them full of just coat the slide pin?
 
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Another observation that at the time I did not think much of it. When I had the rear caliper off of the rear rotor I tried to compress the 3 pistons on the caliper all the way back into the caliper body. I was unsuccessful at compressing the 2 outer pistons back into the body of the caliper ( even with slight pressure from a C-clamp) but the center piston would retract all the way back into the caliper body by hand.
After reading some article I see that the 2 outer pistons on the rear caliper are controlled by the SMC on the left front caliper.
( correct me if I am wrong) but I would think this also lends to the diagnosis of a failing SMC.
 
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If the plunger in the SMC cannot return to its proper position, that tiny relief port in the side does not allow the fluid from the back brake calliper to be relieved. In other words, the back brake remains on.

Why would it not return ? Well over the years, all sorts of gunge accumulates in the top end of the SMC. It doesn't get much flow of fluid, and it is exposed to the elements ( there have been at least 4 designs of the SMC since it was first introduced - mainly to deal with letting water escape from the rubber boot area. moisture gets into the fluid by absorption and if it isn't changed, then bits inside can corrode. Both of these things can stop the SMC plunger from returning to its proper position. It maybe that it needs a damn good clean out, and subsequent proper flushing.
Thanks for all this information, I agree that the SMC is not returning to the proper position after the rear brake pedal is released due to the SMC sticking. Then replacing it and then flushing the brake lines should fix; correct?
Or are you saying that flushing the lines may fix it without replacing the SMC?
I flush my brakes at least every riding season and put in fresh OEM brake fluid.
This sounds like maybe what has been happening to the gold wing when they issued the latest recall and replaced the majority of the brake system components at the dealers.
 

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The guy I bought my bike from couldn't get his rear brake to stop sticking he took it to a dealer and they told him that all they could do was throw parts at it until it was fixed he replaced the SMC that didn't fix it I then replaced the rear master cylinder it helped a bit but didn't fix it so I replaced the PCV which did the trick. But at that point I already knew I had a good SMC and rear master cylinder. Try the SMC it will probably solve your problem as it did on my 03. If not you will have to keep going as I had to on my 04. My 04 was ridden in the winter quite a bit and had a lot of corrosion which I think was the main issue. Best of luck with yours.
 

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Don B said:
One question I have about this thread, what do you mean by RR brake? My ST only has one rear rotor, on the left side of the wheel.
Geeze Louise thank you for asking that Don! I was going nuts trying to figure out WTH he was talking about. I figured it had to be the rear brake but RR? Was there a Union Pacific version along with the ST and PanAmerican and it has two rear discs? Fortunately I still have most of my hair left.
 
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The guy I bought my bike from couldn't get his rear brake to stop sticking he took it to a dealer and they told him that all they could do was throw parts at it until it was fixed he replaced the SMC that didn't fix it I then replaced the rear master cylinder it helped a bit but didn't fix it so I replaced the PCV which did the trick. But at that point I already knew I had a good SMC and rear master cylinder. Try the SMC it will probably solve your problem as it did on my 03. If not you will have to keep going as I had to on my 04. My 04 was ridden in the winter quite a bit and had a lot of corrosion which I think was the main issue. Best of luck with yours.
I am hopeful the SMC fixes it but I realize I may have to replace other components as well if that does not fix it.
 
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John,
I am getting the replacement component (SMC) not the kit.

Those pics look pretty bad. I will take pics of mine when I get it apart.
 
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Here is my Old SMC. You can see it is corroded and the plunger is sticking in the down position.
My bike has almost 113,000 miles before this failed.
Larry Igofar helped me a lot in the diagnosis and the installation of the new SMC - Thanks Larry.
Thanks to all who offered there input.
Thanks to my wife for helping me bleed the brakes.
The new SMC is working great so far, When I depress the plunger it immediately springs back - unlike my worn out one that would stick when pressed down.
FWIW I have ridden thousands of miles on this bike and this is the first time I have replaced the SMC.
It is not a hard job if you buy the entire assembly, ( Thanks Larry for the part number) just swap it out with the no good unit, you just have to be patient when bleeding the brakes. Also I have ridden in a lot of rain on this bike, and never though of drying the SMC area after a hard rain. Now if possible I will try to keep that area as dry as possible.
You can see the weep hole on photo 5 which is not much for the excess water to get out.
I hope this will help someone else out in the future diagnose rear brake drag. I tried to include all my symptoms I was seeing.
The 4th picture shows the SMC piston stuck - it should be flush with the top of the cylinder. But do to the corrosion the spring cannot return it to the home position.

Old SMC.JPGOld SMC 1.JPGOld SMC 2.JPGOld SMC 3.JPGSMC weep hole.JPG
 
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Great job! Thanks for the kind words. I very much enjoyed our chats on the white courtesy phone :rofl1:
Thanks for posting the pictures to help other members.
Ride safe and ride far my friend.
Larry
 
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Fixed:
Took Bike for a test ride and there is no drag what so ever on the rear wheel.
Brakes are nice and firm.
On the center stand I easily get 1 1/4 to 1 1/2 rotation by hand on the rear wheel. - I am using this for a base line from now on.
I'm even coasting up hill. LOL.
 
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