Ok, so to start, one of my first posts on this board was to ask about removing the linked brake system on my (yet undelivered!) 2005 VFR. I was advised to hold the thought and get some miles in first, because I might just like them. Fast forward in time. I've been considering a front fork swap for a while now. But, now that I'm sort of attached to the linked brakes, I'm not sure I want to give them up!
So, give it some thought here and there. What's the big deal? Why are they so nice?
What I came up with for myself is the following, in order of importance based on my personal tastes and priorities:
1. I like how the secondary action of the rear being activated helps settle the chassis when getting ready to pitch into a corner.
2. I like how the front end dive is lessened due to the rear activation causing the rear of the bike to squat slightly.
2a. Especially when riding with a passenger.
3. It has been proven that linked brake systems reduce stopping distance.
So here's my thought and the point of discussion... When the front-rear brake links are deleted, one has a choice of how many of the 3 rear pistons to drive with the rear brake pedal. Most I have seen, block off one piston and simply change out the rear master cylinder to appropriately drive the remaining 2 pistons.
Why not "link" the unused piston back to the front brake master? Ok, so the factory setup drives that lone rear piston via a secondary master cylinder located on the left fork leg(I'm talking 6th gens here). The engineered pivoting action of the left front caliper actuates the secondary master and forces fluid to the rear via the PCV(proportion control valve). Obviously forks from a non-LBS bike will not have the provisions for this setup. Yeah, yeah, all this has been hashed out in other threads already, ok, the REAL point then - find a way to send reduced fluid flow to that lonely rear piston via the MAIN master cylinder, the one at the handlebar.
First thought, is to run a 3-line setup on the front(single line from master to junction tee, + 1 line to each front caliper). Add to this 3-line setup a double banjo bolt which would allow a 4th line to run through the bike to the single rear piston.
The problem there, is that this will apply full line pressure to that rear piston, and I’m not sure this is will yield the desired effect. The desired effect being just enough pressure to create just enough drag to squat the rear a bit…
I need to research the Proportion Control Valve a bit and see what it's specific functions are. Also try to find out how much pressure is applied to the single rear piston via the secondary master on the left fork. This will likely involve calculating sizes of the secondary m/cyl piston and the rear brake piston. I believe the brake lines internal sizes are the same throughout.
Running straight line (meaning, no valving or restriction, just tube) from a splitter at the front MC to this thing which you could mount in place of the old secondary under-seat MC to the rear caliper would give you adjust-ability and what should be a decent mounting location. Tuning will be "fun" but a lot of tuning is anyway. ATGATT fo sho.
[image: View Post]KPerham, on 10 May 2010 - 09:37 AM, said:
Wait, what...?
Don't you already have linked brakes?
Just work on the forks.
Yes, I do. I started this topic to possibly work out a way of keeping some form of linked brakes, after swapping to non-stock forks. Whether I swap or not will be a new topic at another date. I have resprung my forks and have Gold Valves sitting on a shelf... but I still desire USDs and radial monster brakes.
Why did H employ the secondary MC instead of the PCV?
It may be that after you go the PCV route, you may not like the result.
I started to write about the reason why I think so, but couldn't come up with a sane one that I would be willing to commit to 'paper'.
All I'm saying is that PCV is cheaper to manufacture (methinks) than the whole messy set-up that H went with. Yet they still did what they did.
OK. Here goes... :blink:
Maybe it's because PCV will put out a steady % of the pressure exerted by the MC, while the secondary MC driven off the caliper will modulate its output pressure based on the conditions? IDK...
Food for thought.
Yeah, the secondary MC setup gives you a reduction in effect at low speeds. I believe that the brake link is effectively dead below 5 mph. Prop valve is going to give some effect all the way to zero forward motion.
I'm not convinced on the LBS.
I'm not trying to be a condescending jack hole, but YOU are the PCV. Go ahead and use each brake as you see fit...
On the other hand, if you are just looking for an engineering challenge: Have at it! :fing02:
"Radial monster" calipers aren't going to have any provisions for multiple LBS lines so I'm not really sure what you're after here. By not feeding individual pistons, I'd think you would lose the real benefits of LBS and the overall nice balance of the 6gen version.
[image: View Post]KPerham, on 10 May 2010 - 10:13 AM, said:
I'm not convinced on the LBS.
I'm not trying to be a condescending jack hole, but YOU are the PCV. Go ahead and use each brake as you see fit...
On the other hand, if you are just looking for an engineering challenge: Have at it! :fing02:
You jackhole! :dry:
:biggrin: I agree with you, I have seat time on non linked bikes(all my track time was on my F4i). I think it would be cool to keep at least part of the linked brakes. More of an engineering challenge.
[image: View Post]FotoMoto, on 10 May 2010 - 10:14 AM, said:
"Radial monster" calipers aren't going to have any provisions for multiple LBS lines so I'm not really sure what you're after here. By not feeding individual pistons, I'd think you would lose the real benefits of LBS and the overall nice balance of the 6gen version.
Didja read my first post Doug?
Here's a pic to help illustrate what I thought of doing.
[image: Attached Image: VFRLBS.jpg]
[image: View Post]SEBSPEED, on 10 May 2010 - 10:40 AM, said:
Didja read my first post Doug?
Errr, not really. It timed out due to length. :computer-noworky: :goofy:
Going by your diagram, it looks like you lose all the benefits of the rear brake pedal activation partially controlling the front. Again, without control of individual pistons on the front calipers, I see no real "balance" like the 6gen system has and that you value. The front master from any other system won't be designed for additional "help" from the rear. Your schematic looks, to me, like a partially reversed gen 1 LBS design circa 1990.
Ahh, skip all this mental masturbation and adapt a new cbr abs system plus forks to it! :warranty: :laughing6-hehe:
[image: View Post]FotoMoto, on 10 May 2010 - 11:04 AM, said:
[image: View Post]SEBSPEED, on 10 May 2010 - 10:40 AM, said:
Didja read my first post Doug?
Errr, not really. It timed out due to length. :computer-noworky: :goofy:
Going by your diagram, it looks like you lose all the benefits of the rear brake pedal activation partially controlling the front. Again, without control of individual pistons on the front calipers, I see no real "balance" like the 6gen system has and that you value. The front master from any other system won't be designed for additional "help" from the rear. Your schematic looks, to me, like a partially reversed gen 1 LBS design circa 1990.
Ahh, skip all this mental masturbation and adapt a new cbr abs system plus forks to it! :warranty: :laughing6-hehe:
Well, all the stuff I really like about the LBS, is currently controlled by the front master. I don't use the rear for much of anything, so I would be fine with having the unbalanced system.
I guess, to put it in a nutshell, I'm looking to squat the rear of the bike via the front master alone, and without applying excessive rear brake pressure.
[image: View Post]SEBSPEED, on 10 May 2010 - 11:24 AM, said:
I guess, to put it in a nutshell, I'm looking to squat the rear of the bike via the front master alone, and without applying excessive rear brake pressure.
[image: View Post]KPerham, on 10 May 2010 - 11:26 AM, said:
[image: View Post]SEBSPEED, on 10 May 2010 - 11:24 AM, said:
I guess, to put it in a nutshell, I'm looking to squat the rear of the bike via the front master alone, and without applying excessive rear brake pressure.
[image: View Post]SEBSPEED, on 10 May 2010 - 01:13 PM, said:
Nobody wants to play engineer with me?
LOL - I'm an engineer and really dont wannna play engineer with ya.....I'm sure Honda went through all the gyrations that you're thinking of screwing with..... you could just practice using the rear brake....(I'm still stuck on liking brakes separate fr/rr for light bikes.)
Not my kind of engineering, sorry. To be honest this kind of thing is exactly why I would rather revalve, respring, etc the existing forks on the 6th gen and keep the LBS. Well, that, and the cost/hassle factor of a swap to something else.
The thing I will say about this is if you want a simple linked brake system, this works to an extent, and if you want to link back to the fronts you can just build the same system in reverse direction. But what I think makes more sense is to just go towards the rear with pressure and not have it duct pressure back to the front when the rear is applied.
The master cylinder is going to have to be larger because of the extra fluid displacement, by a noticeable percentage of increase.
[image: View Post]SEBSPEED, on 10 May 2010 - 09:21 AM, said:
I need to research the Proportion Control Valve a bit and see what it's specific functions are. Also try to find out how much pressure is applied to the single rear piston via the secondary master on the left fork. This will likely involve calculating sizes of the secondary m/cyl piston and the rear brake piston. I believe the brake lines internal sizes are the same throughout.
Thoughts/Questions/Comments/Concerns?
This is exactly how the braking system on the GL1500 Gold Wing works. I'm not sure theirs even uses a proportioning valve at all, i.e. that one piston on the front wheel only ever gets activated if you use the rear brake, and the rear brake is never activated by use of the front lever.
Have you ridden a 5th-gen lately? I know the linked brakes on the 5th-gen have what some consider a brake balance which is less comfortable than the 6th-gen. Maybe if you ride one and you don't like that it will tell you that nothing but the 6th-gen system will do?
I would love to play engineer here! But alas, there are other problems.
I would personally like to keep the rear giving 1 piston up front some lovin, but if it meant getting USD forks, I guess I could give that up.
Your system is actually pretty simple. And other than the 1 piston in the front, I don't see what the issue is.
Slap some SP2 forks/brakes on, get the adjustable PCV, and run SS lines throughout. :491:
As mentioned it would no longer be so speed sensitive, but that's the price you pay for shedding the only overly complex part of the system, going from back to front. I've started a thread like this before, and the answer was just a simple "no". But I'm glad you want to look into it!
I wanted to keep my original functionality, possibly by stealing the forks/brakes off something that came with what I wanted. With a great lack of outside help, I came up with only two options. Concours 14, and the VFR1200. Neither would be particularly affordable or readily available. And the Conny has electronically controlled (and adjustable) linked brakes/ABS.
I don't think it would be all that difficult of a system to at least rig up and try, though I'm sure it would be lots of fun bleeding that system out.
Going to have to crack open the good ole fluids book and get the whole physics on it, but don't think it's that far of a push. You should be able to get away with the stock MC. It's only one piston, and it's going to be with reduced pressure.
Great topic Seb... I've given this some thought also, and I think Magicman is close with the "adjustable" PCV.
But...
You might find once you have reached high pressure under front braking... the fluid will want to flow to the rear brake. You might find while this flow is happening, you might lose some front braking, and the lever travel will be greater than normal. You may get away with it using a larger dia MC, but then that too has disadvantages. This is just backyard engineering thinking here.
I think this is why Honda went with the 2nd MC on the left fork... so that it didn't affect the front mc actions.
I had an ungaily idea: find a way to attach a cable to the brake lever, and it can actuate a little cable operated m/c under the tank, ala a Guzzi V50.
[image: View Post]Vee-Ef-Ar, on 10 May 2010 - 10:31 PM, said:
Great topic Seb... I've given this some thought also, and I think Magicman is close with the "adjustable" PCV.
But...
You might find once you have reached high pressure under front braking... the fluid will want to flow to the rear brake. You might find while this flow is happening, you might lose some front braking, and the lever travel will be greater than normal. You may get away with it using a larger dia MC, but then that too has disadvantages. This is just backyard engineering thinking here.
I think this is why Honda went with the 2nd MC on the left fork... so that it didn't affect the front mc actions.
My mind boggles on how you can achieve this <headache>... but I'll be watching.
Excellent point. Not sure if that would actually happen if the system was properly bled, but a good point nonetheless. Idea #2 was to run the same splitter up front, but instead of running the rear line from the splitter, run it directly from the master using a double banjo bolt. Would actually make the line shorter too, I think. As long as there is positive pressure from the master cylinder, all seals & lines are in good shape, there shouldn't be any feedback of fluid.
[image: View Post]timmythecop, on 10 May 2010 - 11:59 PM, said:
I had an ungaily idea: find a way to attach a cable to the brake lever, and it can actuate a little cable operated m/c under the tank, ala a Guzzi V50.
Idea #3 was to use a small diameter line (-2, normal brake line size is -3), to push a slave that would actuate a secondary master for the rear. Very similar to the way the VFR clutch works. Cable would be easier/lighter/cleaner/cheaper, aside from figuring out how to make it work in the first place.
Since we would have a bit of "free weight" to play with(removal of stock LBS nets ~10lbs), I think it's fair to say half of that could be added back in and still be able to call the project a success... Hence, finding a way to tap into the speed sensor and actuate that second master electronically with a relay controlled servo could be an option too... with a greater application of force on the SMC depending on speed... (now I'm going out on a bit of a limb!) ... might be easier on an '06+ since the fuel map goes by gear, where you might use a greater force per gear.
Have you thought about using a height or weight sensing proportional valve? You could fab a linkage between the swingarm and the valve and have a brake line running directly from the front master cilinder.
[image: View Post]V4 Rosso, on 11 May 2010 - 06:03 AM, said:
Have you thought about using a height or weight sensing proportional valve? You could fab a linkage between the swingarm and the valve and have a brake line running directly from the front master cilinder.
Nope, care to elaborate on how they would work in this application?
The same as they do on the rear brakes of a car (pre ABS era). It acts as a normal proportional valve where the brake line pressure to the rear brakes is reduced with the increased brake line pressure of the master cilinder. Only now it is further reduced depending on load by adding or lessen the spring preload of the PCV. Preload is set by a mechanical contruction that 'measures' the vertical distance between a fixed point on the vehicle and the rear axle. The harder you decellerate the more weight is put on the front and the more the tail is raised and the less brake pressure can be applied on the rear brakes. You could e.g. put the LSPCV on the swingarm just behind the shock and attach the arm that puts preload on the LSPCV spring to the top shock mount.
So if I clamp onto the front brakes, and it starts to nose dive, the rear brake would let off? That kinda sounds counter intuitive... I thought the point was to GET rear braking to make it squat?
I know the inverse wouldn't be better either, making the rear want to lock up (or trigger ABS) when the weight is off it.
I think a consistent amount of braking in relation to the front would be best. Especially in a panic stop. I want to know EXACTLY how the bike is going to react, with as few variables as possible. Going 2up would completely change the braking with your suggestion.
[image: View Post]magicman, on 11 May 2010 - 09:19 PM, said:
So if I clamp onto the front brakes, and it starts to nose dive, the rear brake would let off? That kinda sounds counter intuitive...
Maximum brake line pressure would be reduced, yes. To get the rear to squat you need maximum braking force at the rear. With an LSPCV you can put more initial brake pressure at the rear and it is automaticly adjusted when the load on the rear tire (grip) decreases.
There are LSPCV that have machanical sensors that measure the height (load) between the erar axle and the vehicle and there are LSPCV that put more preload on the valve spring (reduce brake line pressure to the rear brakes) by means of a steel ball that pushes against the valve spring through inertia.
[image: View Post]SEBSPEED, on 10 May 2010 - 01:13 PM, said:
Nobody wants to play engineer with me?
Yeah I'm in. And as a rider that uses the LBS on his 5th gen to help with his slow feet, I'd like to work this out, so that one day can fit USD's to my VFR.
The only thing I see you losing with your diagram is the secondary MC. It does two things. One it controls the engagement of that single rear piston based on the front wheel applying torque to the Secondary mc through the caliper linkage. So if the front wheel is not trying to rotate forward, that one rear caliper piston does sero, zip, nada.
Now does that matter, I'm not sure. I mean I can't really think of a moment when out riding that I want the front wheel to be completely stopped, that the rear brake caliper using one piston would matter (I mean short of a burnout).
The big question is what size is the piston in the secondary MC? Its going to impact whether you can just plumb to the pcv or whether you have to get an aftermarket adjustable pcv.
Remember the pcv reduces the pressure transmitted to that rear piston in relation to what pressure that MC on the fork leg was developing. That MC could have the same pressure slope as the MC on the bar or it could be a very different rate. Measure the bore and stroke of the SMC and compare it to the bar mounted mc.
IF they are right in line, then you could source a new mc that would yield the proper pressure slope for the area of all the pistons and just plumb the pcv.
If not then you are going to need a new mc and the 3rd party pcv to make it all work.
Its either that or you seriously consider adapting the CBS/ABS from the CBR.
Does anyone know if the cbr 1000 abs forks r long enough? Ive been searchin for a few days to try and find where someone posted the fork length but cant find it anywhere. Even searched cbr forums. The reason i ask is because i would like to upgrade my suspension but want to keep the abs. So goin with somethin that already has abs is the logical next step. But since i live in bfe i dont have access to a dealership like most do.
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