Rear Brake Pedal Sinks When Releasing Front Brake

dduelin · Jul 10, 2016

The proportioning valve divides hydraulic pressure from the rear pedal between the rear caliper and the fronts. It's calibrated to give the rear caliper most of the braking pressure from the pedal until the brake pedal is pressed past a certain crossover point. With just a little pressure on the rear brake the valve proportions little or no pressure to the front calipers. The PCV allows use of the rear brake alone when trail braking, dragging rear brake against throttle for slow speed maneuvers, and when braking downhill on gravel or dirt.

MidLife · Jul 11, 2016

dduelin said:
The proportioning valve divides hydraulic pressure from the rear pedal between the rear caliper and the fronts. It's calibrated to give the rear caliper most of the braking pressure from the pedal

Dave, remember our earlier posts on that? Rear Pedal goes straight from Rear Master to Rear Middle Piston. It is not routed through the PCV. Only SMC to Rear Outers is routed through the PCV. So 100% of the pedal pressure goes to the Rear Middle.

dduelin said:
It's calibrated to give the rear caliper most of the braking pressure from the pedal until the brake pedal is pressed past a certain crossover point.

What you are describing here is the behavior of the Delay Valve. The Delay Valve is the valve that opens up after more pressure is applied to the pedal. Pressure will then go from the Rear Master through the Delay Valve to the Middle Fronts.

dduelin said:
The PCV allows use of the rear brake alone when trail braking,

As said, the PCV is downstream of the SMC. Its purpose is to limit the pressure to the Rear Outers, to prevent lock up.

If you squeeze the front to the grip in an emergency, pressure will go to the Front Outers and SMC will activate the Rear Outers, passing through the PCV. But the PCV will limit the pressure to the Rear Outers to prevent the rear to lock up.

When you are trailing off the front lever, you are relieving pressure on the Front and Rear Outers. Trailing off the pedal relieves pressure on Front and Rear Middle.

What Igofar is pointing out, is that at speed, most the rear braking power is controlled by the front lever, not the pedal.

dduelin · Jul 11, 2016

Ok, I did not understand the plumbing but I do know that light pressure on the brake pedal sends little to no pressure to the front calipers. Thanks for explaining how it actually works. If it is the delay valve and not the proportioning control valve the end result is the same. Honda's LBS in the ST1300 allows use of the rear brake with no or very little front brake which is helpful in certain situations.

In the context of this thread and of cornering techniques, if you have pedal drop it is not normal and can be carefully bled out. If you have pedal drop and you use trail braking you know that when you ease off the last few % of front lever and still have rear brake lightly applied the pedal sinks just when you still need the last bit of rear brake to set corner speed and it takes more pressure or a quick pump to create a hard pedal. The ST benefits from use of the rear brake to settle the suspension while hustling. At the moment of no more front brake I want feel through the pedal to the caliper to the contact patch as accurate as possible instead of correcting with more force or a quick pedal pump for the drop. With no drop the feel through the pedal to the tire is linear when the fronts are eased off.

"What Igofar is pointing out, is that at speed, most the rear braking power is controlled by the front lever, not the pedal."

I hope that my description above clarifies that I'm not talking about most of the rear braking power and none of the front. I'm talking about a delicate touch, a small amount, because at increasing lean angles past turn-in light pressure on brakes is all we can get away with and all that we need. Trail braking to the apex is an advanced skill and it's not for everybody. This might even bring out a reply or two that trail braking has no place on the street and it doesn't if it's not understood and not practiced. If you do understand it and practice it then pedal drop wouldn't be tolerated because it changes the forces acting on the contact patch just when we need changes the least and as much feedback as possible.

Igofar · Jul 11, 2016

Good explanation MidLife.

Igofar · Jul 11, 2016

dduelin said:
Ok, I did not understand the plumbing but I do know that light pressure on the brake pedal sends little to no pressure to the front calipers. Thanks for explaining how it actually works. If it is the delay valve and not the proportioning control valve the end result is the same. Honda's LBS in the ST1300 allows use of the rear brake with no or very little front brake which is helpful in certain situations.

In the context of this thread and of cornering techniques, if you have pedal drop it is not normal and can be carefully bled out. If you have pedal drop and you use trail braking you know that when you ease off the last few % of front lever and still have rear brake lightly applied the pedal sinks just when you still need the last bit of rear brake to set corner speed and it takes more pressure or a quick pump to create a hard pedal. The ST benefits from use of the rear brake to settle the suspension while hustling. At the moment of no more front brake I want feel through the pedal to the caliper to the contact patch as accurate as possible instead of correcting with more force or a quick pedal pump for the drop. With no drop the feel through the pedal to the tire is linear when the fronts are eased off.

Dave, go out to the garage and try this....
Spin the rear tire, then push your smc forward. This should stop your rear wheel instantly!
Now have someone push the rear end of your bike down, raising the front wheel off the ground, and spin the front wheel then apply the foot pedal.
Amazing ain't it, the pedal stops the front wheel as soon as its applied :rofl1:

dduelin · Jul 11, 2016

I assumed as much. It's one thing to describe leading a horse to water and and another thing to ride that horse to the water on a curvy trail.

Igofar · Jul 11, 2016

I guess I'm just jealous that I do not possess the super powers or ability to ride using the force like a Jedi warrior. So your implying that your skill allows you to ride your bike using only the rear brake at will, by feel?
You may want to look at that plumbing diagram again, as anytime the rear pedal is used, it operates the center pistols on all three calipers.

dduelin · Jul 11, 2016

Maybe it's when the motorcycle is moving faster than we can turn the front wheel by hand and slight pedal pressure is applied the delay valve allows just a small % amount of front caliper pressure compared to the 100% amount to the rear caliper. That small % amount to the fronts will stop the front wheel in the lay on the floor and turn the wheels garage exhibition right away but in a dynamic riding situation like trail braking or low speed skill maneuvers it's effectively like no or very little front brake at all, and isn't that what matters, how it works in motion? Whether it's my skill or not, without a doubt the LEOs and other riders that compete in skill rodeos and gymkhanas on STs can ride the rear brake against the clutch friction zone without adding enough front brake pressure to upset the bike in the incredibly tight circles and turns they make.

At the end of it I think we both agree that pedal drop is not normal and can be bled out so the linked brakes work as Honda and The Force intended.

MidLife · Jul 11, 2016

dduelin said:
Ok, I did not understand the plumbing .......

Looks like you had (or have) a VFR? The VFR is plumbed closer to what you were describing earlier, as far as PCV from the Pedal to the Rear is concerned. Maybe that's what stuck in your mind. Honda has so many flavors of linking schemes, not easy to keep up.

dduelin said:
If you have pedal drop and you use trail braking you know that when you ease off the last few % of front lever and still have rear brake lightly applied the pedal sinks just when you still need the last bit of rear brake to set corner speed and it takes more pressure or a quick pump to create a hard pedal.

A matter of personal preferences here. You probably have ridden millions of miles and your brake touch is way more sensitive than mine and you are using advanced techniques. Am more of the occasional and slow poke rider. The front lever engages most of what I need most of the time, all the outers, front and back, this is up to 2/3 of the total available braking power, more than what I would usually need. Only touch the rear for emergencies to add the remaining 1 /3 of power front and back (or also for slow/gravel maneuvering, as you said, or steep downhills).

So by the time I lean in, I am off the pedal anyway and no chance for a pedal drop to become a worry in mid turn and am doing all the brake trailing off on the way to the apex from the front lever (which still engages a respectable share of the rear anyway). It also allows to rest the ball of my foot on the peg, which helps me with staying loose on the grip and bike stability. Again, that's what's working for me. But may also explain why there are others on this board who are not too worried about the drop and just living with it?

MidLife · Jul 11, 2016

Igofar said:
...... as anytime the rear pedal is used, it operates the center pistols .......

Surely more effective than deer whistles!

Igofar · Jul 11, 2016

dduelin said:
Maybe it's when the motorcycle is moving faster than we can turn the front wheel by hand and slight pedal pressure is applied the delay valve allows just a small % amount of front caliper pressure compared to the 100% amount to the rear caliper. That small % amount to the fronts will stop the front wheel in the lay on the floor and turn the wheels garage exhibition right away but in a dynamic riding situation like trail braking or low speed skill maneuvers it's effectively like no or very little front brake at all, and isn't that what matters, how it works in motion? Whether it's my skill or not, without a doubt the LEOs and other riders that compete in skill rodeos and gymkhanas on STs can ride the rear brake against the clutch friction zone without adding enough front brake pressure to upset the bike in the incredibly tight circles and turns they make.

At the end of it I think we both agree that pedal drop is not normal and can be bled out so the linked brakes work as Honda and The Force intended.

While I agree 100% about bleeding will remove it, we must agree to disagree on how your able to trail brake on a bike with linked brake system.
I am sure you will find that when you talk to some of the LEO's that ride the ST1300's that they understand and know that they are simply dragging all their brakes and using engine power and clutch to ride through it.

Update:
Well it appears I was wrong with my last comment about all officers knowing their bikes etc
I spoke with a couple motor officers tonight that do ride ST1300's.
One was a former HD rider and the other from a BMW.
Turns out neither knew their bikes had linked brakes :rofl1:

The both did point out that you would fail motor school if your brake light came on! Clutch & throttle only I was told.

dduelin · Jul 12, 2016

Igofar said:
While I agree 100% about bleeding will remove it, we must agree to disagree on how your able to trail brake on a bike with linked brake system.
I am sure you will find that when you talk to some of the LEO's that ride the ST1300's that they understand and know that they are simply dragging all their brakes and using engine power and clutch to ride through it.

I've already mentioned in posts #23 and #28 that slight pressure on the rear brake pedal sends very little to no effective pressure to the front calipers and allows almost all the braking to be accomplished by the rear brake. This allows trail braking with the rear brake doing most of the braking. I wrongly attributed the front/rear bias to the proportional control valve but the end result is the same. A light touch on the pedal applies almost no front brake. I know this is works in application if I got the plumbing wrong. Mea culpa. I dug around to find out how Honda accomplishes this with the LBS on the ST1300. Here is something that came from the original press packet distributed at the ST1300's release in 2002:

"Linked brake systems use complex hydraulic plumbing with proportioning and delay valves to activate different pistons in each brake caliper. The Honda Linked Brake System (LBS) uses triple piston calipers on two front disks and one rear disk. Each of the three pistons on each caliper are independent, so activating only one piston produces about one-third of the potential braking force on each caliper.

Squeezing the front brake lever activates the outer two pistons of both front calipers, plus the middle piston of the rear caliper. The rear brake pedal activates the two outer pistons on the single rear caliper, plus the middle pistons on both front calipers. Applying the fronts also provides about 30% of rear braking--not so much as to cause a rear wheel lockup. Applying the rear pedal contributes to approximately 30% of maximum front wheel braking."

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. At slow speeds, trailing the rear brake helps control speed without bringing the bike to a sudden stop."

The key is that the LBS passes only 1/3rd of the total braking force applied by the pedal to the front caliper and 2/3rds to the rear. A light touch on the rear applies a correspondingly much lighter touch to the front brakes........pressure is applied to the fronts but so little as to not make itself known as if it would be if the bias was 50/50.

A riding exercise that illustrates how little front can be applied with the pedal trailing off is to take the bike smoothly to about 30 mph with intent to slow to 25 rather quickly. Using the front brake to brush off 5 mph will readily compress the forks. Using the rear brake to scrub off 5 mph doesn't compress the forks nearly the same amount and when the pedal is eased off the forks don't extend and upset the suspension.

T_C · Jul 12, 2016

dduelin said:
"Linked brake systems use complex hydraulic plumbing with proportioning and delay valves to activate different pistons in each brake caliper.

I thought there was a few seconds delay between rear brake pedal and 'effective' front brake engagement. So long as you were just momentarily using a little rear brake you wouldn't really feel it up front.

Igofar · Jul 12, 2016

dduelin said:
I've already mentioned in posts #23 and #28 that slight pressure on the rear brake pedal sends very little to no effective pressure to the front calipers and allows almost all the braking to be accomplished by the rear brake. This allows trail braking with the rear brake doing most of the braking. I wrongly attributed the front/rear bias to the proportional control valve but the end result is the same. A light touch on the pedal applies almost no front brake. I know this is works in application if I got the plumbing wrong. Mea culpa. I dug around to find out how Honda accomplishes this with the LBS on the ST1300. Here is something that came from the original press packet distributed at the ST1300's release in 2002:

"Linked brake systems use complex hydraulic plumbing with proportioning and delay valves to activate different pistons in each brake caliper. The Honda Linked Brake System (LBS) uses triple piston calipers on two front disks and one rear disk. Each of the three pistons on each caliper are independent, so activating only one piston produces about one-third of the potential braking force on each caliper.

Squeezing the front brake lever activates the outer two pistons of both front calipers, plus the middle piston of the rear caliper. The rear brake pedal activates the two outer pistons on the single rear caliper, plus the middle pistons on both front calipers. Applying the fronts also provides about 30% of rear braking--not so much as to cause a rear wheel lockup. Applying the rear pedal contributes to approximately 30% of maximum front wheel braking."

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. At slow speeds, trailing the rear brake helps control speed without bringing the bike to a sudden stop."

The key is that the LBS passes only 1/3rd of the total braking force applied by the pedal to the front caliper and 2/3rds to the rear. A light touch on the rear applies a correspondingly much lighter touch to the front brakes........pressure is applied to the fronts but so little as to not make itself known as if it would be if the bias was 50/50.

A riding exercise that illustrates how little front can be applied with the pedal trailing off is to take the bike smoothly to about 30 mph with intent to slow to 25 rather quickly. Using the front brake to brush off 5 mph will readily compress the forks. Using the rear brake to scrub off 5 mph doesn't compress the forks nearly the same amount and when the pedal is eased off the forks don't extend and upset the suspension.

You've still got it wrong Dave...
The front lever operates the outer pistons (2) per caliper on the front rotors only = 4 pistons
When they grab the rotors, the SMC then goes to work sending the signal to operate the outer two pistons on the rear caliper = 6 pistons.
The foot pedal operates the center piston on all three calipers = 3 pistons.
When you use both brakes, front and rear lever at the same time, wait for it....you use how many pistons?
So when you think your using less force, its simply because when you use just the foot pedal, your only applying one piston to each caliper.

Igofar · Jul 12, 2016

You cannot "trail" the rear brake only by using just the foot pedal, you are simply using one piston on all THREE calipers when you apply the foot pedal. You are applying braking to both wheels whether you realize it or not.
You may find out the hard way, thinking your just using your rear brake, when going into a turn and finding sand or debris on the road and having your front wheel slide out from under you because the pedal is ALSO applying braking force to the front wheel. What you are in affect doing by using just the rear brake pedal in an attempt to trail brake, is just using one piston, thus less braking.

MidLife · Jul 12, 2016

Igofar said:
You cannot "trail" the rear brake only by using just the foot pedal, you are simply using one piston on all THREE calipers when you apply the foot pedal. You are applying braking to both wheels whether you realize it or not.

At speed, left center front will cause the SMC to engage and activate the rear outers (with less force than if front lever was engaged though, but will still activate) so you end up with 2 on the front and 3 on the rear.

Igofar · Jul 12, 2016

You are correct, you replied before I could edit my reply.
Thank you for your reply.
Yes you are using more pistols in the rear due to the smc, however you are still not trail breaking because you are also using the front brakes by using the rear lever.

MidLife · Jul 12, 2016

Igofar said:
......however you are still not trail breaking because you are also using the front brakes by using the rear lever.

Not sure we have the same understanding of "trail breaking"?

The instructor at my MSF course back then explained "trail braking" like it is defined in Wikipedia today:

"Trail braking is a motorcycle riding and driving technique where the brakes are used beyond the entrance to a turn and are gradually released up to the point of apex."

If any braking is done beyond the tip-in point, front or rear, it is "trail braking".

Recently, Rekoob recommended the book "Sport Riding Techniques" by Nick Ienatsch which expands on "trail braking". A good article from Nick on "trail braking" can also be found here .

Igofar · Jul 12, 2016

Good point and information on what the technical term means.
However, the point I was trying to make was you can't separate the front and the rear system of the brakes while applying them at any point in the turn no matter how gently, easy, or pressure used.

Igofar · Jul 12, 2016

All this talk of technical riding techniques is way over rated!
Real skill is blasting down a blue groove and backing into a turn on a bike that does not have any brakes.
Try pitching your steed sideways at 80 mph plus in a controlled slide with nothing but throttle control with a dozen other riders trying to do the same thing within inches of each other :rofl1:

Rear Brake Pedal Sinks When Releasing Front Brake

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