well rear brake locked up

the Ferret

the Ferret

Daily rider since May 1965
Joined
Feb 5, 2008
Messages
1,940
Age
74
Location
So-Oh
Bike
21 NC750 14 CB1100
2025 Miles
004127
Wife and I were out for a nice leisurely evening ride. We were coming up to a stop sign 2 miles from home when all of a sudden the rear brake locked throwing us into a slide. I managed to keep it up. After a minute at the stop sign it started to roll so i headed for home but it was dragging bad. i made it home but the rear brake disc was fire red, and it smelled horrible. Sat for a few minutes and I was able to push it into the garage. Guess I will have the shop pick it up and access the damage. Nuts.
 
Classic symptoms of a smc (secondary master cylinder) lockup. Lots of threads to be read,,, on the topic. Unsafe to ride until a new one is installed,,, and then go through the entire proper brake system bleed process. I was right were you likely are,,, about 18 month ago. Who ever tackles your brake system (and verifies that the rotor is not warped,,, and rear caliper is not damaged) needs to spend some time reading up on the whole process. Experts on this forum will be your best source of information,,, Cat'
 
If you do your own maintenance, I'd suggest doing it yourself. Its not difficult, but you will spend the time doing it right whereas paid mechanics (unless you have a good mechanic) might take shortcuts. And you don't know what corners they might have cut unless you ask.

As an example, I took our car back to Toyota for a 40K check (free since we bought the 2 yr old car from them last year). I was told the brake pads were worn down (they were correct - I checked and measured them later) and I needed new pads and rotors. This is a 2015 car w/ 41K miles on it. I asked if they change the brake fluid and flush the system. Nope, they don't do it unless a caliper is replaced. "Its not needed", I was told. So I asked our regular mechanic, and pointed out that brake fluid is hygroscopic. He said yup, it is, but people don't want to pay for it, so we don't do it unless asked or the system is opened.

Were I in your shoes I'd order a new SMC and replace it, then take the old one apart and see if I could salvage it - then I'd rebuild it and put it on the shelf for future use.
 
Well, that sucks! Glad you were able to get home without too much trouble.

Looks like the CB will be getting some more attention...
 
I'm not capable of this repair. It will be going to the shop.

Yea Pat, CB will see some more miles lol
 
I had that happen on my 2010 a couple of years ago, only I was right in front of my house, so I didn't drag the rear disc like you had to do to get home.

I had to rebuild the SMC, the Rear MC and the rear caliper. Then bleed the entire system.
 
Not being a ST13 owner, yet? Is there any way of releasing this brake pressure to enable you to ride on, albeit I would think with restricted braking. It seems it would be a bit of a nightmare if on a long ride days from home. Or is it all about preventative maintenance beforehand?
Just interested to know. Glad you got home safe, must have been a bit of a moment!
Upt'North.
 
Yea Doug, Di was on the back. A bit of a fright for her as i didn't have time to explain what what happening at the moment. She thought I hit an animal she said.

I have my bike brakes serviced regularly, smc cleaned, fluid bled, new pads, but I do ride daily in all weather. 109,900 miles on this one.

Thinking about it last night, and knowing others have had the issue, I am sort of afraid of the bike now. Might be time for another bike.

I am headed down to the shop on my CB in an hour or so, and will have them pick it up and have a look at it, but it might just be a write off/trade in at this point.
 
i have had this happen also , thats why i carry a spanner as an emergency to release the pressure
cause by this . it not safe when the hot fluid shoots out :eek:

but its a slow drive home and its gets you out of a bind.

regards

tony
 
I'm thinking. Why not disconnect it completely? Like don't need it!
 
Upt' North said:
Not being a ST13 owner, yet? Is there any way of releasing this brake pressure to enable you to ride on, albeit I would think with restricted braking. It seems it would be a bit of a nightmare if on a long ride days from home. Or is it all about preventative maintenance beforehand?
Just interested to know. Glad you got home safe, must have been a bit of a moment!
Upt'North.
Click to expand...


Because the SMC is low on the front wheel of the bike where It can pick up all kinds of water and muck, while it’s a good idea to regularly change the brake fluid once a year, you can still have problems with water entering the SMC and causing corrosion. I think it unlikely this problem happens all at once. For that reason I recommend putting the bike on the center stand with the bike in neutral and spin the rear wheel to check for binding. I would do it every day on a trip At least once a month otherwise.

You definitely don’t want to be having close calls like the OP had!
 
Upt' North said:
Not being a ST13 owner, yet? Is there any way of releasing this brake pressure to enable you to ride on, albeit I would think with restricted braking. It seems it would be a bit of a nightmare if on a long ride days from home. Or is it all about preventative maintenance beforehand?
Just interested to know. Glad you got home safe, must have been a bit of a moment!
Upt'North.
Click to expand...

If you carry 8 mm spanner or socket, you can release the pressure to free it up (easier with a MP bleeder check valve and a short piece of hose so you don't get sprayed).
HOWEVER, since the brake system is LINKED you will not be able to operate EITHER of the brakes without it locking up again.
So yes, you can release the pressure and gently ride if off the road, however, if you chose to ride it home, you would be doing so very carefully without touching the brakes :rolleyes:
 
Trump said:
Because the SMC is low on the front wheel of the bike where It can pick up all kinds of water and muck, while it’s a good idea to regularly change the brake fluid once a year, you can still have problems with water entering the SMC and causing corrosion. I think it unlikely this problem happens all at once. For that reason I recommend putting the bike on the center stand with the bike in neutral and spin the rear wheel to check for binding. I would do it every day on a trip At least once a month otherwise.

You definitely don’t want to be having close calls like the OP had!
Click to expand...

Good habit to get into, however, if you want to be sure, spin both wheels, as the front wheel dragging can active the SMC and cause the rear wheel to lock also.
 
Igofar said:
If you carry 8 mm spanner or socket, you can release the pressure to free it up (easier with a MP bleeder check valve and a short piece of hose so you don't get sprayed).
HOWEVER, since the brake system is LINKED you will not be able to operate EITHER of the brakes without it locking up again.
So yes, you can release the pressure and gently ride if off the road, however, if you chose to ride it home, you would be doing so very carefully without touching the brakes :rolleyes:
Click to expand...
I think I have to disagree with this, unless my understanding is in error. As I am looking at the service manual and how the front brake works I see this: The front brake lever applies pressure to the outer pistons of both front calipers, then the SMC activates the proportional control valve and applies pressure to the rear outer brake pistons. So, if you open the bleeder valves of the rear caliper there should not be any pressure applied to the rear caliper from the front linked system, when the front brakes are applied.
 
Igofar said:
Good habit to get into, however, if you want to be sure, spin both wheels, as the front wheel dragging can active the SMC and cause the rear wheel to lock also.
Click to expand...


Whoa o a thanks for that never occurred to me. These linked brakes are more diabolical than I imagined!
 
Thanks Ray. We had just done 31 miles of a 33 mile loop of 168 left and right 55 mph curves around my house.. Luckily it happened on a straightaway as I was coming up to a stop sign.

Talked to head mechanic at the shop today. He also rides a Goldwing with SMC. He said if his ever locked up he would just bypass it, which is what Goldwing Trikes do and what he is suggesting to do to mine. New caliper rebuild, new mc rebuild and a new rotor he's guessing before he gets it on his bench for an actual inspection next week.
 
Thanks for the replies, Larry and STB, I think I can see both points, ie if you effectively disable the rear brake then you would be left with front brakes only but also as it is linked wouldn't this also disable the front brake. Hand on heart I don't understand the system well enough to make my own decisions but it's a very interesting conundrum. I think that the answer would lie in whether the only connection is the SMC or is there an auxiliary link.
Thanks again and I'm sure the discussion isn't over. I hope not anyway because it is extremely relevant to every ST13 owner. I'm not one yet and there are no immediate plans to change that but I can't see many alternatives as a replacement in due course.
Upt'North.
 
This SMC linked braking system is a definite negative for the St1300 beast. I try to be proactive and do all kinds of preventative maintenance but it seems this locking brake phenomenon can just appear out of the blue. Not something I want to deal with on a long ride.
 
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