Questions on diagnosing brake drag

Joined
Aug 25, 2006
Messages
16
Location
Alabama
Bike
2006 ST1300
I just got back from my first Spring ride to check everything out and got the dreaded brake drag. I guess it's dreaded, I never heard of the problem before reading here about it after getting back. I think this actually happened to me once a few years back but I parked the bike when I got home (thank goodness I was a block away after riding for 4 hours) and the problem had disapeared when I came back to it. I never had another problem until today. It started dragging, I tapped the foot brake and it quit, so I came home. The bike is an '06 and it's never had the brakes touched. It's only got 23,000 miles on it.

1) How do I diagnose exactly what the problem is? I assume it's the SMC but I'd like to be sure before buying a new one.

2) Assuming it is the SMC, do I have to get this from the dealer?

3) Again, assuming it's the SMC, is it necessary to rebuild all the cylinders? Would replacing the SMC and bleeding everything be sufficient?

I've read here that rebuilding the SMC can be tricky. I'd be more comfortable replacing and maybe rebuilding the old one at my leisure as a spare. Maybe.
 
Joined
Jan 8, 2011
Messages
7,065
Location
Arizona
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2007 Honda ST1300A
Search the articles section on avoiding the pitfalls, that should get you started. If you need further help, PM me a contact phone number and I will call you on the white courtesy phone and try to assist you.. :call:
 
Joined
Nov 1, 2009
Messages
387
Location
North Plainfield, NJ
Bike
'06 ST1300A
I just got back from my first Spring ride to check everything out and got the dreaded brake drag. I guess it's dreaded, I never heard of the problem before reading here about it after getting back. I think this actually happened to me once a few years back but I parked the bike when I got home (thank goodness I was a block away after riding for 4 hours) and the problem had disapeared when I came back to it. I never had another problem until today. It started dragging, I tapped the foot brake and it quit, so I came home. The bike is an '06 and it's never had the brakes touched. It's only got 23,000 miles on it.

1) How do I diagnose exactly what the problem is? I assume it's the SMC but I'd like to be sure before buying a new one.
Diagnosing brake drag on the ST1300 is pretty straight forward, the most difficult task will be remembering to have a 8mm wrench on-hand. As this event is most likely to be 'roadside', a high degree of caution is needed. Traffic maybe nearby! The brakes will be hot! The muffler will be hot! The brake fluid will be hot, and under pressure! Brake fluid damages painted surfaces!

1. The next time brake drag is noticed, find a safe place to stop and put the motorcycle up on the center stand.
2. Confirm the rear wheel is causing the drag, by trying to spin the wheel by hand. It should spin with minimal effort.
3. Confirm the drag is not caused by road debris caught up in the rear wheel.
4. The rear brake caliper has two bleed screws, by opening these bleed screws one at a time, the hydraulic brake circuit that is holding pressure can be determined.
5. Carefully open the forward bleed screw (located at center on the top of the caliper).
1. If fluid exits under pressure, this indicates that the hydraulic circuit from the rear master cylinder is not releasing properly. Close the bleed screw.
2. Try to spin the rear wheel by hand.
3. If the rear wheel spins, the problem most likely involves one or more components between the rear brake caliper, and the rear master cylinder.​
6. If the rear wheel is still dragging:
7. Carefully open the rearward bleed screw (located at rear, on the side of the caliper).
1. If fluid exits under pressure, this indicates that the hydraulic circuit from the secondary master cylinder is not releasing properly. Close the bleed screw.
2. Try to spin the rear wheel by hand.
3. If the rear wheel spins, the problem most likely involves one or more components between the rear brake caliper, and the secondary master cylinder.
4. If fluid exited under pressure from both bleed screws, this may indicate that the hydraulic circuit from the rear master cylinder is not releasing properly.​
8. If the rear wheel is still dragging:
9. As the opening of the two bleed screws of the rear brake caliper has released all hydraulic fluid pressure in the caliper, any continued brake drag is most likely due to a mechanical issue preventing the brake pads from releasing.
2) Assuming it is the SMC, do I have to get this from the dealer?
Not necessarily, purchase the part from your favorite parts supplier. The current replacement secondary master cylinder part number is: 06454-MCS-G03

3) Again, assuming it's the SMC, is it necessary to rebuild all the cylinders? Would replacing the SMC and bleeding everything be sufficient?
Assuming the problem is the SMC, then replacement, and bleeding maybe all that is needed. However this is a good time to flush & bleed the entire hydraulic brake system.

I'm including a couple of links to some sketches of the Honda Dual Combined Brake System as used on the ST1300, for your amusement.

DCBS Components

Linked Brake System
 
Last edited:
OP
OP
Joined
Aug 25, 2006
Messages
16
Location
Alabama
Bike
2006 ST1300
Sorry I'm just now getting back to this. Thanks for the info. Fortunately I'll be doing this in my garage, not the side of the road.
 

Kevcules

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2008 ST1300
Sorry I'm just now getting back to this. Thanks for the info. Fortunately I'll be doing this in my garage, not the side of the road.
I think he meant if your brakes suddenly started to drag while you were riding and left you stranded on the roadside, then following his instructions will help you determine what and where the problem is coming from.
I just bought an 08 and am learning about the dreaded SMC failure. I just bled my clutch and brake systems with some help and a few emails to Igofar , so hopefully with good maintenance , I won't have any issues. Good luck with yours....
 

Mellow

Joe
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The bike is an '06 and it's never had the brakes touched. It's only got 23,000 miles on it.
Well... 11 years old and no brake bleeding maint at all? That's the first issue, I would start there.. it might be your only problem if you're lucky, just contaminated fluid w/crud in it that's affecting optimal operation of the system...
 
OP
OP
Joined
Aug 25, 2006
Messages
16
Location
Alabama
Bike
2006 ST1300
Well... 11 years old and no brake bleeding maint at all? That's the first issue, I would start there.. it might be your only problem if you're lucky, just contaminated fluid w/crud in it that's affecting optimal operation of the system...
Good point. Can it cause the brakes to actually stick, as opposed to just degrading their performance?
 

Mellow

Joe
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'21 BMW R1250RT
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Good point. Can it cause the brakes to actually stick, as opposed to just degrading their performance?
Absolutely, you might have moisture in there or crud and that can cause the fluid to expand rather than hold pressure and release that pressure. Also, the crud could be hindering the flow of the fluid somehow.
 
OP
OP
Joined
Aug 25, 2006
Messages
16
Location
Alabama
Bike
2006 ST1300
Well in that case I have a 2006 Infiniti and a 2006 Chevy truck that probably need flushing too. :)

One more thing - I've seen references here to the proper sequence to flush/bleed the brakes as given in the service manual. All I have is the owners manual which doesn't mention it. I did a (very) quick look through some links but did not see it outlined. Can someone point me to a link if there is one or even where I can get the service manual?
 
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