Linked system de-linked

[rossilvr]

Hello all,

I have (or better say had) a very strange cause of my rear break drag (see "Irresolvable rear brake drag" thread I have posted previously). After reading everything regarding the rear break drag on this great forum, and after trying to fix the problem myself for a year, and after having the bike at a HONDA dealer for one month and replacing the Secondary Master Cylinder, delay valve, proportional control valve, rebuilding the rear master cylinder and all break calipers, following the right procedures while bleeding, checking all parts for mechanical wear, you name it... ...I had no other option. I am not by any means suggesting to anybody to do this!!! It just seems that for me it was the only option.

Yes, I would still rather fix the problem but after spending so much money with no result and with the riding season at full swing I had no other option. I want to ride "drag free"

And finally after "20K+ dragging" kilometres I had a pleasant ride to work today.

So what did I do?

Drain the SMC/rear break circuit as per the manual. There are two hoses running from the rear caliper (middle piston and the outer two pistons) to the rear master cylinder (MC). They are attached on top of each other on the MC by a doublehole bolt (or however it is called).

I used to lower hose (going to the middle piston /rear caliper) and attached only that one to the MC by a singlehole bolt. Done.

So I now have a separate front and rear break on my ST. I would say the stopping power is down by maybe 10% which I am ok with regarding the neverending story with my rear break. The front break stopping power feels the same.

The next thing I am going to do is order two steel braided lines for the rear break so I can run one to the middle piston and the second one to the outer two pistons - this will increase the stopping power. Now with the one piston it is not sufficient.

And I am goign to fill up the Secpndary master cylinder (left front caliper) with break fluid in plug it up so it doesnt move so much when I apply the front break. And actually I can now also get two steel braided lines for the front break and get rid of all the complicated plumbing of the front break.

As I said, it is kinda sad I couldnt solve this and after so long and so much money I am sure it is some stupid little thing not functioning properly. The ST is a great bike and I dont want to give up on it. I may look for a total with a working break system and install the whole thing once I get my hands on it.

rossilvr

 

[Blrfl]

Your system isn't entirely de-linked. The fronts are still actuated by the rear pedal.

--Mark

 

[rossilvr]

Your system isn't entirely de-linked. The fronts are still actuated by the rear pedal.

--Mark

Hello Mark,

actually it isn`t. The lower hose goes only from the rear MC to the caliper. I have the breaklines off the front mid piston so if what you say would be true I would have break fluid all over the place. I am using the green line form your picture that is on the right side from the break pedal. I do not have the ABS model so I do not have the modulator. Just one hose from the pedal to the piston.

rossilvr

 

[nldaniel]

Oh my, you did fully de-link it.

By doing it this way, you disabled 4 of the 9 pistons, likely to be a sizeable chunk of braking power thrown away.

I considered a similar approach when my SMC kept on giving me problems. I considered removing and/or blocking the line from the SMC to the rear caliper, leaving all other lines intact. This way you would at least retain full front braking power.

I recommend you look into this possibility, to regain some of the lost braking power.

Regards, Dani

 

[bkra13]

Just remember that the bore in the rear master cylinder probably isn't sized correctly for the 3 pistons on the rear caliper. Your braking performance may actually go down.. someone may need to do some volume testing on that..

 

[rossilvr]

Oh my, you did fully de-link it.

By doing it this way, you disabled 4 of the 9 pistons, likely to be a sizeable chunk of braking power thrown away.

I considered a similar approach when my SMC kept on giving me problems. I considered removing and/or blocking the line from the SMC to the rear caliper, leaving all other lines intact. This way you would at least retain full front braking power.

I recommend you look into this possibility, to regain some of the lost braking power.

Regards, Dani?l

That is great thought and I considered it as well. But then for some reason the rear pedal starts pumping break fluid in to the two outer pistons in the rear calipers and starts dragging as well.

Did you solve your SMC problem?

 

[nldaniel]

The rear pedal feeds the outer pistons in the rear caliper trough the SMC only. blocking the line from the SMC to the rear caliper will stop the pedal from applying force to the outer pistons.

my problem was really solved after rebuilding the SMC. however, during the rebuild I changed rear pads and introduced a new problem. I bent one of the tabs on the anti-rattle spring, causing my inner brakepad to sit crooked, causing drag. I thought it still was the SMC.. Now my rear wheel does 2 revolutions after a firm push.

 

[rossilvr]

You are absolutely right - that is something I didnt realize. I think I have a problem with the feeding hose that goes form the rear master cyclinder into the reservoir. That is that last possible cause of my drag. IF it is some debris in the rear MC causing the drag and me changing all the parts/valves - that will be unbelievable. Will let you know. Taking it apart tonite.

The rear pedal feeds the outer pistons in the rear caliper trough the SMC only. blocking the line from the SMC to the rear caliper will stop the pedal from applying force to the outer pistons.

my problem was really solved after rebuilding the SMC. however, during the rebuild I changed rear pads and introduced a new problem. I bent one of the tabs on the anti-rattle spring, causing my inner brakepad to sit crooked, causing drag. I thought it still was the SMC.. Now my rear wheel does 2 revolutions after a firm push.

 

[bkra13]

Good diagram of the system here..

http://stwiki.notonthe.net/twiki/bin/view/ST13/LinkedBrakingSystem