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Discussion Starter #1 (Edited)
Hi All, I'm a bit of a defender of the DCBS and hope to share my thoughts on the system, so that new owners will have a better understanding of how the system works and how they can improve the Bird's standard braking performance. I read a lot about how riders only use the front brake lever, however they are not utilising a third of the braking performance built into the system (technically not correct but you'll get what I mean :smilebig: ). Using the foot lever, results in generating a lot more clamping force on all three discs, especially the front two disks which is what we want. I ride a Blackbird on the road, track days and motogymkhana. Using the front lever activates two pistons in both front calipers which then causes the front left caliper to rotate and 'activate' the secondary master cylinder (SMC) mounted on the left fork leg. The SMC then applies hydraulic pressure to two pistons in the rear caliper. I have no choice other than to apply front and rear brakes at the same time. However, if i require more braking power (i.e. at the end of a long straight ??), I'll use the rear brake lever which then activates a third piston in all three calipers. Because there is now more hydraulic pressure being applied to all three calipers, the front left caliper will press harder on the SMC which in turn transmits even greater pressure to the two pistons in the rear caliper. Now i have all three pistons in all three calipers doing work. I can also apply a greater pressure through the foot brake lever (i.e. legs are a lot stronger than your right hand!) which further increases hydraulic pressure to the two centre pistons in the front calipers (higher clamping force) which in turn causes the SMC to generate a higher pressure to the two rear caliper pistons. The proportioning control valve (PCV) will however, regulate the pressure to the two rear pistons. If i apply too much pressure with my foot or hand which results in over pressurising the SMC circuit to the rear two pistons, a valve in the PCV will reach a preset level and will open which reduces hydraulic pressure (gradually to a set limit and always maintaining pressure for braking) to the two rear pistons to prevent rear wheel lock up (although it can still lock). But i can still apply greater foot brake pressure to the front centre pistons. That's a lot of clamping force and a lot better braking performance than just using the front brake lever! I didn't bother mentioning the delay valves function in the two front calipers centre piston circuit. No electronics involved. At least, I think that's how the Honda Dual Combined Braking System (DCBS) works. Thanks to fellow CBRXX.com members for the two SMC valve images. Please let me know if you have a different thought on the system. Cheers :thumb:

DCBS Front.PNG DCBS Rear.PNG DCBS1.JPG DCBS2.JPG DCBS3.JPG DCBS4.JPG DCBS5.JPG DCBS6.JPG SMC Alignment.jpg SMC check valve assembly 1.JPG SMC check valve assembly.jpg
 

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I'd like to also add that the delay valve also works as an anti dive unit as it brings the fronts after the rear has been activated.
 
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Discussion Starter #3
I'd like to also add that the delay valve also works as an anti dive unit as it brings the fronts after the rear has been activated.
Hydraulic pressure from the rear master cylinder is applied directly to the front left caliper without delay. When pressure rises to a set level, the delay valve opens and pressure is then applied to the front right caliper at which point you can then apply a great deal of pressure to all centre pistons (especially the front!) giving you a lot of braking power which 'front brake lever only' riders are missing out on. The whole point to my post :) It's more of a squat inducing valve then an antidive unit ;)
 

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Yep
 

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I dont care how it works, But it does work and I love it, Yes, Im a front lever only, Bird rider,
Back wheel locked up one day, when I used the rear brake, The rear pedal piston was covered with grime and wouldnt let go,
Bit of a clean up on the side of the road and all was working again,
Every now and then I use the back brake pedal now just to make sure its still working,
Coming down a long steep gravel road, I use the gears and back tyre to slow down,

Compared to my Bonnies 8 inch twin leader, Which I refused to use as it put me on the deck,
Locked up if you even breathed on it,
It was back to second and drop the clutch, Harsh, But it worked also,
 
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Nothing beats a good braking technique....... long gone are the bad old days when HD riders used to only use the rear brakes on their raked out 70's choppers (and many riders died as they just couldn't stop in time......).

I use both brales, all the time, but I vary the pressure used at each end to suit the application. There is an excellent Utube video I saw on the KTM forum..... best I've ever seen that explains the why/how/what for, really well...... I'll try to find it again - it's a brilliant reminder of why we need to refresh our thoughts and break any old habits...... a few minutes viewing could save a life.... :eyebrows:

PS I searched and searched, but couldn't find the video, so ask Dr Google if anyone wants to refresh their braking technique's........ it's well worth doing just to make sure no bad habits have crept in over the decades..
 

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Hi, I've been looking up as much as I can about the linked brakes on Hondas. I have a VFR which has a slightly different SMC position, but many similar problems... Currently my rear brake is locking up due to the SMC and I'm waiting a rebuild kit.
I was just wondering what your thoughts are on the plastic valve inside the SMC. It isn't documented on the ST1300 or VFR service guides. I thought it was a one way valve at first until I found the 0.25mm hole. I feel it's purely to assist in bleeding, as without it when trying to bleed the front (rear circuit) brakes it could suck old fluid or air from the rest of the circuit through to the front... Has anyone drilled or removed the spring in it?

Does this happen to a lot of Blackbirds? (I was thinking of getting one but after this VFR linked brakes issue I'm put off anything Honda until I'm confident in my ability to repair them).

Also does anyone include this SMC as part of regular maintenance? I plan to use ACF50 grease around the piston as I ride all seasons, to hopefully prevent any future issues.
 

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I wouldn't modify that puck in any way. Take note of its orientation. Then carefully take it apart clean it out and put it back. It's a very simple design that if kept clean and fluid swapped every 2 years max should never be an issue.
 
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I wouldn't modify that puck in any way. Take note of its orientation. Then carefully take it apart clean it out and put it back. It's a very simple design that if kept clean and fluid swapped every 2 years max should never be an issue.
I will also say since wrapping the PCV bleed nipple in ptfe tape to avoid air ingress during bleeding (not covered the hole in the end) that I also find it very hard to pull fluid through via vacuum. Foot pedal pushes fluid thru easily. Anyone else notice this?
 

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I've always used pedal or the handle to bleed the systems. Vacuum only works to get the bulk of the fluid into the system. Then I use the handles to finish always. Then I'll quick flick them with the cover off the masters to work out the last bits of air.
 

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I will also say since wrapping the PCV bleed nipple in ptfe tape to avoid air ingress during bleeding (not covered the hole in the end) that I also find it very hard to pull fluid through via vacuum. Foot pedal pushes fluid thru easily. Anyone else notice this?
Ahh so that is where the pcv bleed nipple is fitted! Birds W/S manuals say bleed the PCV but there are no bleed nipples on any of the Birds I have ever worked on.
I also use manual methods to bleed the system on the Bird even though I have a vacuum bleeder (I'm old school) .... but I add in a manual pump of the secondary master cylinder push rod when bleeding the rear caliper just to make sure that it sees new fluid.
 
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