Un-Linking Front Brakes on 2nd Gens (and later)

[Fred W]

This thread was split off of a troubleshooting discussion about soft rear brake situation on a second Gen FJR. It was posed in that thread that the FJR linked braking system may not be all that desirable t some riders, but nobody has yet described exactly what technical problems would need to be overcome to do that.

The way that the FJR's Linked Braking system is designed is different than some other manufacturer's "linked" systems. It only links one of the front brake caliper pistons to the rear brake pedal (under certain predetermined conditions) but not the reverse. The rear brake does not get applied when pulling the front brake lever. One front piston is dedicated to the rear foot pedal. The linking is designed to only apply that one front piston after a set, fixed fluid pressure level has been exceeded in the rear circuit, and then there is a proportioning valve to apply pressure on the one front piston and the rear caliper together.

The upside of this kind of a linked system is not entirely clear. Maybe someone else here will be able to explain the intended goal of having it.

One of the down sides of having this type of linked system is that the front brake power (mechanical advantage at the lever) is reduced by 25% since one of the four front caliper pistons is dedicated to the linked function from the rear.

Another disadvantage is that one cannot be certain that the front brake will not be applied when jabbing at the rear pedal, which may be something you want to do under certain circumstances.

Yet another disadvantage is that the added complexity of the linked system makes the rear brake less reliable and more difficult to service properly. There are far more problems and complaints with the rear brakes on 2nd Gens and later than with the old 1st Gen's unlinked system.

Considering these disadvantages some owners may want to un-link their brakes (at their own risk of course).

This thread is to discuss what sort of problems one might encounter in undertaking such a project, and how that might be accomplished by someone assuming they were willing to take on the risk of such an unauthorized modification of their own brakes.

Neither I, nor anyone else on any internet forum, are responsible for your safety. You should not make unauthorized modifications to the braking system on your motorcycle as it may result in an unsafe condition for you and any passengers you are carrying. This thread is not a tutorial on how to defeat this feature. It is a only discussion of what would happen if one were to defeat it, and how it might have been done.

 

[Cosmin]

Hi Fred,

Thanks for splitting the topics, I know this has been debated for some time but I didn't find a thread which has a positive output...
(related threads:
https://www.fjrforum.com/forum/index.php?showtopic=140782
https://www.fjrforum.com/forum/index.php?showtopic=28486
https://www.fjrforum.com/forum//index.php/topic/8137-linked-and-abs-equipped-motorcycles/page-1
https://www.fjrforum.com/forum//index.php/topic/7746-linked-brakes-and-abs/)

BTW - has anyone on the forum SUCCEEDED a delink?
In my case the main reasons why I would want that are:

1) being able to use ONLY rear braking in curves; today as soon as the front is engaged (while using rear braking) there is a dive plus the trend of a 'raised' motorcycle from leaning position. This is the main reason I miss my previous 'classic' brakes motorcycles on winding roads;
2) having the possibility to use rear brake only while going downhill on non-tarmac roads.


If I remember correctly, our bikes have 5 connections on the ABS module:

- feeding from rear master cylinder;
- feeding from front master cylinder;
- output to proportioning valve (and further to rear caliper);
- output to metering valve (and further to front right caliper - 2 pistons);
- output to the other 2 pistons in right front caliper and all 4 from left front caliper.

I found these guys (https://www.whaccessories.com/Spiegler.htm) who can provide some custom brake lines/hoses/connectors. Basically what we need:

- a custom rear hose from rear caliper to the relevant ABS port; I think from threads-size point of view also the existing one (which connects to the proportioning valve) fits - it's just a matter of bending a little the metal pipe from the end of the main hose (don't know if this could jeopardise the integrity of the line);
- a plug to block the ABS port which was going to the metering valve (or plug the exit from the metering valve);
- a custom short hose which should interconnect the upper right caliper feeder with the lower one (including a long banjo bolt which should pass 2 overlapped connected hoses ports - I am not sure I explained accurately).

That's it, job done

A few immediate effects:

- higher force might be needed to be applied on the lever for front pump since it was not designed/sized to feed 8 but only 6 pistons;
- no change in rear lever force needed. Though a sooner ABS intervention might be noticed in emergency brakes especially with low/no weight on rear (no pillion, no luggage);
- for those who use only front brake in most situations a bigger dive could be noticed due to increased front brake force;
- don't know if the plugged connection on the ABS could cause further issues during bleeding operations?!
- otherwise - you'll notice the pleasant effects of using separate brake circuits front/rear

))



Now please let me know what I've potentially missed from the plan...

 

[RossKean]

With respect to Gen II rear brake problems, I wasn't aware that they were any worse than Gen I. In fact, there have been a lot of Gen I ABS failures compared to later FJRs. (I realize that this has nothing to do with linked brakes.)

One comment on restoring the fourth front piston pair to work with the front lever, You won't get back all of the potential (4 piston pair) braking capacity because the lower right pair is smaller diameter and will provide less braking force than the other three piston pairs.

Interesting topic. I don't think I would consider the modification since I have had NO issues with the way the current system works. I don't need a solution for what is (to me) a non-existent problem.

One suggestion is to make sure that the modification is easily reversible. This could be important when it comes to selling your bike. If the purchaser has an accident that could be attributed to brake function in any possible fashion, plan on hiring a lawyer because the purchaser will. When it comes down to it, ANY accident could be attributed to a brake function issue if the prosecution has the right "expert" witness.

 

[Ignacio]

To be clear, I am casting stones at this. I'm not one that thinks that I will (or need to) try and out-think Yamaha engineers on this.

One of the down sides of having this type of linked system is that the front brake power (mechanical advantage at the lever) is reduced by 25% since one of the four front caliper pistons is dedicated to the linked function from the rear.

This 2006 Review when it first came out suggested otherwise. "Take heart, expert rider, the system is supposed to be pretty unobtrusive; the front brake is separate from the rest of the system."

This thread is to discuss what sort of problems one might encounter in undertaking such a project, and how that might be accomplished by someone assuming they were willing to take on the risk of such an unauthorized modification of their own brakes.

I would think the most simple would be to go buy the braking hardware from a Gen 1 non-ABS bike (i.e. brake lines, master cylinders) and revert back to like it's 2003. Why stop at just the linked brake part? Why not take other things out while you're at it that some people think are undesirable?

You might get lucky that you could somehow use existing calipers with some semi-custom plumbing or maybe a subset of the ports. But then you might not and then have to also worry about calipers and forks.

And then I'm not sure if the engineers dialed in their suspension with linked brakes in mind....

Yet another disadvantage is that the added complexity of the linked system makes the rear brake less reliable and more difficult to service properly.

Consider me one of those that thinks this is related to some people not servicing them properly and probably wouldn't also service a non-linked system properly either.

Sorry, but it just adds up to the notion to me that if you really don't like linked brakes that have been in FJRs for now over a decade...you should go buy a Gen 1 non-ABS bike and be done with it. Probably far easier and less risky for the demographic that your giant red disclaimer hints at.

 

[Fred W]

Let me clarify:

The proposed goal is not to eliminate the ABS. ABS good. Keep ABS.

The proposal is to only eliminate the rear to front linking, which was introduced with the 2006 model year. Going back to non-ABS 1st Gen is not desirable. Going back to the earlier version non-linked ABS braking system of a first Gen is not desirable either as the ABS on 1st Gens was a cruder system. Maintaining the superior later version of ABS of a 2nd Gen (and later) would be desirable after eliminating the linking function.

Can anyone explain what the linking was intended to accomplish? I can not for the life of me figure that out.

 

[Ignacio]

Can anyone explain what the linking was intended to accomplish? I can not for the life of me figure that out.

Googling I found this article:

The advantage of linked brakes is that the rider can control brake bias between front and rear wheels, within the limits of the system. At speed, linked brakes help balance braking between front and rear, making front trail braking in corners more predictable.

Translation: To make it easier for 90% of non-hardcore-racer riders mash the brakes more often and receive generally better outcomes than a non-linked bike.

Let me clarify:
The proposed goal is not to eliminate the ABS. ABS good. Keep ABS.

Noted. But, still the same principle: Collect and install parts from a Gen 1 ABS bike and go back to 2005. Not all of those 12-14 year old ABS blocks are froze-up quite yet.

 

[Cosmin]

First of all - it's obvious that this topic is addressed to those who are considering the de-linking. It was discussed several times about the associated risks (like at a bike resell etc) and about the fact that many consider the delink useless.

So, getting back to those who are evaluating such a mod, some additional facts:

- the linking was installed first on (mainly touring) bikes especially for balancing the brake forces rear/front and avoid/diminish wheel lock risk in emergency situations;
- in many cases linked brakes do not get along well with sport riding on curvy roads (mainly due to the lack of possibility to use the rear brake ONLY);
- one interesting linked brake system is the one used in BMW: pedal activates rear brake ONLY, lever activates front calipers plus one piston in the rear. So rear braking on winding roads is not affected;
- the changes proposed in the topic above are quite popular on other bikes - for my previous CBR1100 XX (Blackbird) I used a delink kit from UK without issues (straight forward installation procedure - indeed, no ABS involved but Honda CBS was also quite complicated with a third master cylinder etc). So also for FJR if we find a kit or hoses produced by a dedicated brake accessories manufacturer no issues should occur, so people should not be that reluctant.

 

[Bounce]

The upside of this kind of a linked system is not entirely clear. Maybe someone else here will be able to explain the intended goal of having it.

The first time I heard about it was when the GL1800 was introduced. They link a pot to the front via the pedal and also a pot to the back from the hand lever. The intent was to mitigate the impact of stops where a rider used only the pedal without any front input leading to kicking out the rear or, vise vera, washing out the front.

The use of both brakes is taught in MSF but (at least at the time) the majority of riders out there hadn't taken an MSF and the myth of flying over the handle bars if you used any front bake was still out there.

 

[Fred W]

One comment on restoring the fourth front piston pair to work with the front lever, You won't get back all of the potential (4 piston pair) braking capacity because the lower right pair is smaller diameter and will provide less braking force than the other three piston pairs.

Valid point. The unified brake caliper cylinders are different diameters, which would result in differing amounts of piston thrust for a given amount fluid pressure.

Left side Caliper cylinder inside diameters 30.23 mm × 4

Right side Caliper cylinder inside diameter (for unified brake) 33.96 mm × 2, 22.65 mm × 2

The upper right pistons are slightly larger than the cylinders on the left side caliper, which would produce slightly more thrust for a particular amount of fluid pressure than the pistons on the left side, and the lower unified pistons are significantly smaller, which would cause a lot less thrust force per amount of fluid pressure.

The ratio should be linear. So the upper pistons will clamps the pads at 33.96 - 30.23 / 30.23 * 100 = 12.3% more than the left side pads, and the lower (unified) pistons will clamp the pads at 22.65 - 30.23 / 30.23 * 100 = 25.1% less than the left side pistons.

It would still be an increase in total brake force, but not 33% as you would expect by increasing from three pairs to 4. It would be a (22.65 / (33.96 + 30.23 +30.23)) * 100 = 23.98% increase in front brake force. Still worthwhile, IMO.

And the front brake pads would continue to wear unevenly, as they do now.

 

[Fred W]

Basically what we need:
- a custom rear hose from rear caliper to the relevant ABS port; I think from threads-size point of view also the existing one (which connects to the proportioning valve) fits - it's just a matter of bending a little the metal pipe from the end of the main hose (don't know if this could jeopardise the integrity of the line);

- a plug to block the ABS port which was going to the metering valve (or plug the exit from the metering valve);

- a custom short hose which should interconnect the upper right caliper feeder with the lower one (including a long banjo bolt which should pass 2 overlapped connected hoses ports - I am not sure I explained accurately).

That's it, job done

I agree, that seems to be all that is needed.

And actually, you may be able to leave the rear brake line as stock, and leave the proportioning valve in there doing nothing since there will be no unified brake line path anymore, there is nothing to proportion it to. But eliminating the proportioning valve (eventually) would be good for simplicity.

A few immediate effects:
- higher force might be needed to be applied on the lever for front pump since it was not designed/sized to feed 8 but only 6 pistons;

I don't think so. Because of the increased total slave cylinder area the front brake lever may need to move further, but the brake lever effort will be reduced by the increase in area, and the increase in friction area will result in more brake power applied to the front wheel.

- no change in rear lever force needed. Though a sooner ABS intervention might be noticed in emergency brakes especially with low/no weight on rear (no pillion, no luggage);

I agree, the rear ABS may actuate easier because you will no longer be diverting fluid to the front unified brake circuit. But you'll also have a stronger rear brake for the same reason. It's possible that eliminating the proportioning valve would reduce fluid resistance even more.

- for those who use only front brake in most situations a bigger dive could be noticed due to increased front brake force;

Well, not really. Front end dive is proportional to total front braking power and softness of front suspension, but you would naturally use less lever effort to produce the same amount of total front brake power to stop from a given speed in the desired distance. So brake dive shouldn't change.

What you might find is that it is easier to set off the front ABS due to the increased available braking power.

- don't know if the plugged connection on the ABS could cause further issues during bleeding operations?!

That is an unknown and well worth considering. Maybe use a bleeder screw as the plug for the ABS block port?

 

[Bill Lumberg]

I have found no issue with the linked brakes on my 14, and I was very happy with the fully linked/servo'd brakes on my old RT. But I did encounter folks that had issues with worn out components on older bikes, and they wanted to go caveman and keep the bike running without spending money on repairing the OEM system. I think the exploration would benefit those folks. Not to mention these discussions always learn me stuff I didn't no about how these systems function.

 

[Mr_Canoehead]

The upside of this kind of a linked system is not entirely clear. Maybe someone else here will be able to explain the intended goal of having it.

The first time I heard about it was when the GL1800 was introduced. They link a pot to the front via the pedal and also a pot to the back from the hand lever. The intent was to mitigate the impact of stops where a rider used only the pedal without any front input leading to kicking out the rear or, vise vera, washing out the front.

The use of both brakes is taught in MSF but (at least at the time) the majority of riders out there hadn't taken an MSF and the myth of flying over the handle bars if you used any front bake was still out there.

^^ This^^

I still come across riders (mostly on cruisers) who tell me that they don't use the front brake.

 

[Cosmin]

A few immediate effects:- higher force might be needed to be applied on the lever for front pump since it was not designed/sized to feed 8 but only 6 pistons;

I don't think so. Because of the increased total slave cylinder area the front brake lever may need to move further, but the brake lever effort will be reduced by the increase in area, and the increase in friction area will result in more brake power applied to the front wheel.

This is actually a valid concern: in order to actuate the additional 2 pistons, the front master cylinder needs indeed a longer travel but also slight increased effort. At least that's what I experienced in the past on the Honda Blackbird but I got used to it. A friend of mine who was frequently going on track with his Blackbird finally installed a radial-type front master cylinder (after delinking) and improved significantly the front brake feel and confort.

 

[Fred W]

The effort increasing doesn't make any sense. But, the Honda linked system was/is different than the FJR's as there was an additional master cylinder on one of the front calipers that actuated the rear brake under heavy braking. Removing that may have caused increased lever effort? Not sure.

I still believe that lever effort would be reduced on the FJR if you went from 3 pairs of pistons to 4.

 

[Cosmin]

I still believe that lever effort would be reduced on the FJR if you went from 3 pairs of pistons to 4.

I don't want to start an argument - I just remember from the Blackbird that together with longer travel of the lever the sensation was also of extra effort needed, perhaps it was just an impression?! I'm too lazy to start digging in memories for some physics formulas and compute pressure (P=F/S etc ) ) and try to conclude on this but I have another tangible example: some years ago when I upgraded the brakes of a previous sports-car I changed only the front calipers with those from the model with higher power (2 pairs of pistons instead of one pair - overall an increase of ~40% in pistons area) but I didn't touch the master cylinder and servo. The immediate effect was some sort of lack of help from the servo (increased effort from the pedal). The model from which I 'borrowed' the calipers had from factory also increased diameter master cylinder and 1 inch higher diameter servo.

 

[RossKean]

I think that physics will tell you that "Work" (moving the pads in) is a function of force times distance. Moving the pads to the point of contact for four pairs is more "work" than 3 pairs. Since the cross-sectional area of the master cylinder hasn't changed, the increased volume of hydraulic fluid that will be needed is going to translate to a longer stroke.

This, however, has nothing to do with braking power. After the point of contact, the only work (in physics terms) is bulging the lines with the increased pressure. I don't know if it is possible to predict what's going to happen with a specific amount of pressure on the lever. You can calculate the total number of pounds of pressure being applied to the rotors with a given pressure on the brake lever based upon the relative area of the MC piston and the slave pistons but can you calculate whether it is more effective to have 12 square inches of brake pad contacting the rotor at 100 PSI pressure vs 16 square inches at 75 PSI? (both should take similar force on the lever) There is stuff going on at microscopic levels that I don't understand - i.e. compression of pads, temperature changes and how the textures of the pads, sintered metallic particles and rotor surfaces interact. I suspect that smarter people than me have worked all of this out and there is a clear answer (somewhere)?

Perhaps this is the sort of thing you have to try and then adjust the theory accordingly? Anyway, I will be interested in the result; even if I have no intention of de-linking and trying it myself. FJR brakes (front and rear) have plenty of stopping power (for me) and I have never experienced any control issue with respect to the front linked piston. I have never felt that the front wheel behavior was compromised while using the rear brake. Your experience may differ...

 

[Fred W]

I have no intention of modifying my brakes either. As others have said, they work fine as is. This is more of a winter time mental exercise (for me) than the planning of a modification.

Maybe there is an error in my logic somewhere. Here's how I thought of the physics:

When you change the size of the pistons in a hydraulic system, to get increased mechanical advantage, and therefore more force delivered by the slave per unit of input force at the master, you could either reduce the diameter of the master cylinder or increase the diameter of the slave cylinder. In either case it would require the master to move further to produce a given amount of movement of the slave, but the power of the movement would be increased by the same amount.

Adding a 4th pair of pistons is the equivalent of increasing the area of the slave cylinder, so more total clamping power will be applied to the brake pads per lb of force on the lever, at the expense of more lever motion being required to apply that lb of input force.

The increase in area of the added brake pads is a wash. Total friction is independent of the contact area (Ref) so the increased hydraulic force of the added pistons should produce more frictional force at the wheel.

 

[RossKean]

I agree with it being more interest and mental exercise.

You can calculate total force based upon the relative areas of the master and slave pistons and the force per square inch with the pad area thrown in. I understand the theoretical aspects of force/friction/area as per the reference you provided.

The theory, however, breaks down when you consider the physical real world interactions. The same friction over a smaller area means that the temperature at the point of contact will be higher. A significant temperature change will affect the coefficient of friction by affecting the chemical and physical properties of the materials in contact.

Also, your article mentions that the theory breaks down if you are getting enough force to cause the object to "dig in". This is exactly what happens when you consider the sintered metallic particles interacting with the rotor surface. The effects of pad (and) rotor ablation will vary as a function of the amount of pressure at the point of contact - the "tearing" force will be in some way proportional to the absolute pressure at the contact point. Sort of the way that tires wear faster with aggressive braking and acceleration. With the tires, the contact area remains the same but the forces per square inch are higher with aggressive riding. The same total energy (work) applies in each case. Whether braking requires more lever force or not remains to be seen but brake temperatures and wear should be less.

I am not sure how this will translate to the real world but I am sure that it isn't necessarily as simple as it would seem at first glance. Again, let's do the test and adjust theory as needed.

(This is me sitting here waiting for a Nor'easter and a foot of snow expected to hit later today. I expect that it has already hit your area.)

 

[Fred W]

The biggest obstacle to this idea of delinking is that the brake system on the FJR was designed as a system. We are (mostly) all in agreement that having ABS on a street bike is of considerable value. That ABS was designed to operate with the braking power of the linked design. The big unknown, which creates a potential safety problem, is that none of us know exactly what effect if any de-linking would have on the function if the ABS system. Add to that the possible liability / insurance concerns and the idea becomes increasingly less palatable.

But getting back to the question I asked earlier, what exactly was the goal of the Yamaha design engineers when they came up with this particular flavor of unidirectional brake linking?

If their goal was to idiotproof the system for riders with the bad habit of using only the rear brake, then they really didn't go far enough. Unlike the Honda Goldwing system described in that article as "Integrated Braking" where the front and rear are applied in a nearly correct front/rear bias when using only the pedal, the amount of front braking you get from the rear pedal of the FJR is too little to make pedal only use a safe option.

Physics says that at maximum brake force the weight shifts forward onto the front end and unweights the rear tire, completely in good traction, so that the vast majority of the available brake force is coming from the front wheel. Unless the rear pedal is capable of lifting the rear wheel and producing maximum front brake power, which the FJR's linked system is not, then doesn't a design encouraging the improper use of the rear pedal alone become detrimental to overall rider safety?

And if the intent wasn't to do that, then what was it intended to accomplish?