All of a sudden, my rear brake is locked - Where to start first

[Shawn K]

Had a nice 220-mile ride today. Everything felt great, right up to the end.

My driveway slopes downward to the garage, so I always back it in from the street. When I tried to pedal it back, I felt a lot of resistance that increased rapidly, to the point that by the time I got to the garage, I had to have help pushing it back to its spot.

When I got it up on the centerstand, I was unable to turn the rear wheel at all by hand. Oddly enough, the brake rotor wasn't super hot or discolored.

So now I'm not sure which direction to head. My linear thinking says it's one of two things:

1) Brake system needs to be bled - This was my knee-jerk reaction, thinking that maybe I had water in the brake system that needed to be exorcised. After sitting for a while, the rear wheel started turning again, so part of me thinks that this is the culprit.

2) SMC going bad - There's much to be said about this being a known weak point. If I'm having an issue with the SMC, I don't struggle with replacing the entire assembly with new. After all, mine is a 2003 model with 82K on it, and the part's not that expensive.

Since the wheel locked up in my driveway (after multiple braking zones in the last mile) but let go after the bike sat for a while, I'm not sure what's the most likely culprit and best place to start.

What say the experienced guys here? @Igofar - Your thoughts?

 

[Catmandu2]

Option 3) - All of the above

 

[Shawn K]

Yeah, that's kind of what I'm thinking, too.

 

[Coop]

Option 4. the 14mm bolt holding the rear caliper is out.

 

[Igofar]

Standing by the
PM me a contact phone number, and I'll call and get you sorted out.

 

[Rob20111]

When stuck it would be helpful to crack open the bleed screw and see if it releases the brake. If yes then that would indicate a fluid issue rather than mechanical.
Otherwise a good flush and bleed (correct sequence for linked brakes) and pull the caliper for inspection of pads, pistons, slider pins etc.
Clean re grease and re assemble.
Have you recently done any work on the brakes?

 

[SMSW]

Honda recommends changing the brake (and clutch) fluid every two years. Doing it sooner simply keeps the components of the brake system cleaner and gets rid of any tiny air bubbles. Your bike is 17 years old - it certainly won't hurt to service the brakes including a bleed. If you are going to replace the SMC, a complete bleed (there really is no other type) is mandatory. Don't forget to grease the pivot bearing for the front left caliper assembly (SMC pivot on the fork).

 

[Jeff F]

Option 4. the 14mm bolt holding the rear caliper is out.

I thought this too. It could be true, but when the caliper stopper bolt loosens off the whole caliper rocks forward and pinches the brake line slamming on the rear brakes. A very rude thing to have happen to you. Other words come to mind as well.

And a rider would see that caliper thingy out of place, ... if he looks down there that is.

Its possible the caliper falls back into place by itself disguising the problem, but prolly not.

 

[Shawn K]

After talking to Larry the ST Whisperer (), I've decided to bite the bullet and install a new SMC, some OEM brake pads front and rear, and a full system flush/bleed. I'll take a look at my rear caliper bracket soon, and I may replace it as well.

Since I'm doing that much, I might as well strip the bodywork, bleed the clutch, flush and fill the coolant, check the valve clearances, wire up the Cancel switch on my Rostra cruise, replace the tail light bulbs, and whatever else comes to mind. I'll call it "doing my part to stimulate the economy".

 

[Igofar]

When stuck it would be helpful to crack open the bleed screw and see if it releases the brake. If yes then that would indicate a fluid issue rather than mechanical.
Otherwise a good flush and bleed (correct sequence for linked brakes) and pull the caliper for inspection of pads, pistons, slider pins etc.
Clean re grease and re assemble.
Have you recently done any work on the brakes?

Not always true.....if a piston is sticking, canted, or crooked for whatever reason, and you release pressure from the line, it may/could allow the caliper to straighten itself and appear to correct the problem.
You need to determine if it is a fluid/pressure issue, or a binding with pressure causing it issue.

 

[Blackpowder70]

I went through the same issue just months ago. I ended up replacing the SMC, new OEM pads front and back. Then full brake fluid change and bleed. Oh and had to bite the bullet on a new rear rotor due to warping from the rear brake dragging. IGOFAR helps guide me through the repair.

 

[socket462]

I am fairly new to ST1300'S.. What is an SMC? Valve?

 

[Obo]

I am fairly new to ST1300'S.. What is an SMC? Valve?

The secondary master cylinder. It's on the front wheel by the brakes and handles the linked braking.

Here's a thread on it: https://www.st-owners.com/forums/threads/st1300-secondary-master-cylinder-rebuild-smc.133460/

 

[Shawn K]

SMC = Secondary Master Cylinder

It's the pivoting part on the left fork leg that the brake caliper attaches to, and is part of the linked braking system that activates the rear brake when the front brakes are applied.

 

[Shawn K]

@Obo - We must have hit Enter at the same time.

 

[Obo]

Took me a bit to look up the link for the article but yes, great minds think alike.

 

[pmatulew]

I'm right there with you. Realized the other day coming off a highway jaunt that the bike wouldn't roll. Had to pry the rear caliper loose with a big screwdriver. Rear rotor cooked.

Had the rear caliper apart and didn't find any answers there. Spent some time searching here and followed the symptoms. Rear locked or dragging? Clunky clatter from the front? Worse when it gets hot? "Here's your sign!"

Checked the SMC and it wouldn't move at all. Took it apart and it was stuck and gunky. It wasn't too nasty so I cleaned it out and put it back together. (If you decide to refresh yours, make sure the snap ring is fully seated.) Short commute today and it might be okay. Unfortunately now I've lost trust in it. Not good for a healthy relationship.

Following sage advice from village elders I ordered a complete replacement assembly so I can change it out and be done with it. Will see how I feel about it once the part arrives.

 

[Shawn K]

(If you decide to refresh yours, make sure the snap ring is fully seated.)

I decided to avoid the Christmas rush and just replace the entire SMC assembly and replace all the brake pads with OEM pads. So far, it seems to work a treat. Weather permitting, I'll be out defying Governor Leghorn this weekend.

Oh yeah... use OEM brake pads. Pretty significant physical differences from aftermarket.

 

[SMSW]

Checked the SMC and it wouldn't move at all. Took it apart and it was stuck and gunky. It wasn't too nasty so I cleaned it out and put it back together. (If you decide to refresh yours, make sure the snap ring is fully seated.) Short commute today and it might be okay. Unfortunately now I've lost trust in it. Not good for a healthy relationship.

Replacing the SMC has solved the problem for others here who reported the same - a corroded or gunked up SMC. It will probably make your brakes work like new.

 

[Blackpowder70]

Been through the bad SMC and cooked rear brake rotor. I ended up replacing the SMC and full set of OEM pads. But I recommend a full brake fluid change and bleed while your at it.