ST1300 - rear brake drag

mdee

Joined
Jul 8, 2022
Messages
7
Location
Billerica, MA
Bike
2003 ST1300A
Hello, this is my first post to this forum. I have been riding motorcycles, and occasionally self-mechanicing them for 30+ years.
I have briefly read the articles 'ST1300 Brakes - Avoiding the Pitfalls 2020' and 'ST1300 - Brakes - SMC Remove and Refit', which helped educate me on the (too complex) brake system.
This Summer I bought a 2003 ST1300 ABS, 26000 miles, from original owner. I have not done any mechanic work on the bike and no one else has since I bought it. I have ridden it total of 200 miles, on short rides. My longest ride was 2 hrs. I did not notice any brake drag during those rides. I have used both front lever and rear pedal regularly while riding.

Yesterday's ride after about 10 miles I felt braking (not me applying the lever / pedal) when I let off the throttle. Unsure of which wheel, front or rear, I rode 1 mile home. Immediately at end of that ride, the rear caliper / rotor / wheel were hot. I could not turn rear wheel by hand. The front rotors were cool and the wheel turned ok by hand. A couple hours later, once cooled, the rear wheel would turn by hand, but not easy.
Now on center stand and jacked front wheel off ground, turn individual wheel by hand testing: Pressing the foot brake pedal stops each rear and front wheel. Pulling hand brake lever stops front wheel, but not the rear wheel.

Does the SMC action require the front wheel to be spinning while pressing the hand brake lever, to send brake fluid to rear caliper? (I think yes.)
Is there a way to test / see the SMC movement action on the bike?
What should I do to diagnose this issue?
 
Have someone spin the rear for you, or lay beside the bike and use your toe to spin it. Press on the top of the SMC- towards the fork... trying to compress the little plunger there. It should not take a lot of pressure to stop the rear.
If the wheel is hard to turn or has drag you should be able to hears the pads dragging on the rotor!

Having just had to replace a SMC, and reading a lot of stuff on the site..... I think everyone will agree that a 2003 with 26,000 miles is a prime candidate for SMC failure, especially if the brake system hasn't been fully flushed about every 2 years at most.

There are a couple of people on this site that know these bikes inside and out, up and down. I suspect the title of this post will catch their attention soon!

Scott
 
Prepare to go on hold while he chases a rattlesnake out of his garage!!!

(It will give you time to actually do all the little tasks he has been telling you to do)
 
TerryS said:
Can it find lost 10mm sockets? Asking for a friend...
Click to expand...
It's all in the training. Does a hunting dog point at an eagle or turkey vulture? Not owning such a dog, I really don't know the answer to this so the question is rhetorical. Which brings up a better question, why not have trained 10mm socket sniffing dogs?
 
Thanks to the members of this forum and their Articles, I have learned much. Including that the rear brake pedal activates all three pistons of the rear caliper.

With bike on center stand, I have been testing. With rear caliper on bike, I used flat crowbar to pry the outer brake pad tab away from rotor to release the pads dragging on the rotor. It requires much leverage to pry them open enough to eliminate the drag. Then when I step on the brake pedal, the rear wheel again locks tight. Leaving bike sit overnight, the drag reduces some.

To find if the pistons are stuck, and to isolate each brake line circuit, I opened each of the two rear brake line bleeder screws individually, then pried:
First, I opened the middle bleeder screw. About an inch of fluid self-drained and a few very tiny air bubbles. The fluid is amber color. Prying did not retract the caliper pistons and did not push brake fluid out the bleeder screw. I closed the bleeder screw.
Second, I opened the outer bleeder screw. Prying easily retracted all three caliper pistons and pushed couple inches of fluid out the bleeder screw. The fluid is same amber color as from the middle bleeder screw. Tiny air bubbles, more than a few, in the fluid. I closed the bleeder screw.
Then there was no brake drag and the rear wheel would spin free.

I know the brake fluid is old and needs to be replaced. I will do that after resolving the issue. The three caliper pistons retracted easy using the crowbar, thus they are not the cause. I assume the rear master cylinder is not the cause, because the two brake line circuits originate at same point at the rear master cylinder. The remaining components in the outer pistons circuit: Brake Lines ; PCV ; SMC ; Delay Valve.
Something is behaving like a one-way valve after the brake pedal is released.
 
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