How Do the Brakes Work

Joined
Apr 23, 2017
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2008 ST1300 ABS
So I spooned on tires, rear pads, new rear bearings. I just for a joke wanted to spin the wheels and check out the brakes. On the center stand, I leaned the bike on front tire. Spun the rear with my hand and squeezed the front brake. Nothing. Put the bike on the rear and spun the front and hit the rear brake, the front tire stopped. I have ABS. Is this normal in a no run standing position? Or regardless, the front brake should have stopped the rear to when I spun it? No engine running, just standing/sitting, nothing on. I should have tried to search for this one, but I don't think I would have posed the right words to do a search for it. Still learning this bike.
 

CruSTy

My Perception is my reality.
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The front lever should apply the front and if there is rotational load on the left front caliper the SMC will apply rear caliper. The rear foot brake should apply the rear and front calipers using different pistons. It has a complex hydraulic system which includes a secondary master cylinder mounted on the front left caliper. Add the ABS and Bleeding can be a challenge. There are some good diagrams posted here somewhere. This may be one of the most discussed topics here. I will add a link if i find them.

[url]http://stwiki.notonthe.net/bin/view/ST13/LinkedBrakingSystem





[/URL]
 
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ST Gui

240Robert
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EA6BMECH said:
On the center stand, I leaned the bike on front tire.
Are you mis-remembering? The front tire should already be on the ground when the 1300 is on the center stand.

There is an extra bit below the left front caliper is the Secondary Master Cylinder. In proper working order activating the front brake causes the SMC to grab the front rotor. If the rotor is spinning the SMC is torqued causing pistons (2?) in the rear caliper to apply pressure to the rear rotor. Since the bike wasn't moving there was no braking applied. (I think I got that right.)

There's a lot to know about the care and feeding of the SMC as well. It's often overlooked by those of us who think the LBS is just magic.

Your brakes would seem to be responding normally. The Linked Brake System is complicated but separate from your ABS (which has no effect in your test scenario). If I got any of that wrong you'll know shortly. You're not the only one still learning!


CruSTy said:
This may be one of the most discussed topics here.
Ain't that the truth. But of the MDT it probably has the most factual information.
 

wjbertrand

Ventura Highway
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Test the function by pulling forward on the left front caliper while someone else tries to spin the rear wheel. Try it again without pulling on the front left caliper and compare and you will see how it functions. As said before there's no forward movement of the left front caliper unless the front wheel is rotating when the brakes are applied. This is all hydraulically managed so does not depend on electrical power and is independent of the ABS system.
 

dduelin

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You can check the action of the front-to-rear link by lying on the ground next to the left side of the bike. Head towards the front, feet to the rear. The left front brake caliper is mounted on a bracket that pivots on lower part of the fork leg. Take a hold of the caliper on the bracket and push it forward. It will (should) move slightly to the front about 2-3 mm. This applies the rear brake through that pushrod that connects the caliper to the top of the fork leg. Do this a few times to get used to pushing the caliper forward on it's pivot. When released it should move back to the relaxed position. It doesn't take much effort and you certainly do not want to topple the bike off the stand.

Now push the rear wheel with one foot to rotate it. It should easily move with a push of the foot. It won't really spin but it will easily move. Do this a few times to practice moving the wheel with a foot shove. When you have that down push the caliper forward while trying to rotate the rear wheel. The action of the caliper moving forward should prevent you from being able to move the rear wheel. If you have a helper they can rotate the rear wheel while you push on the front caliper.
 
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OP
OP
EA6BMECH
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2008 ST1300 ABS
Dang!! Haha! I feel like one of the "New Kids on the Block". All the years messing with bikes and I'm stumped. I'll check it all out. Thanks for the info peeps!! :)
 
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I go through understanding the brake system all over again every year when I service it- new brake fluid, and a good bleeding. It's not simple! However, once it is bled, I forget all about it for the rest of the year-it's THAT dependable. I have tried a MityVac hand pump vacuum bleeder, but I keep coming back to the Motion Pro check valve type bleeder for an easy time of it.

There are many good articles on here on the brakes,well worth the reads!
 

CruSTy

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Bleeding the brakes on the ST1300 can be a challenge, but the procedure is the same either with or without ABS.
The procedure may be the same but ABS provides more places for those pesky air bubbles to hide.
 
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The procedure may be the same but ABS provides more places for those pesky air bubbles to hide.
No such thing as a free lunch. We get the advantages of ABS, the added complexity of the system with the ABS hardware, plus its cost and maintenance issues. How many of us are going back to buggies, buggy whips, and horses in lieu of cars and motorcycles?
 
OP
OP
EA6BMECH
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:doh1: That's right...........as I slouch in my chair..........:oops: Well I hope to stick my head in the door at TWO and talk to some of ya.:)

Are you mis-remembering? The front tire should already be on the ground when the 1300 is on the center stand.

There is an extra bit below the left front caliper is the Secondary Master Cylinder. In proper working order activating the front brake causes the SMC to grab the front rotor. If the rotor is spinning the SMC is torqued causing pistons (2?) in the rear caliper to apply pressure to the rear rotor. Since the bike wasn't moving there was no braking applied. (I think I got that right.)

There's a lot to know about the care and feeding of the SMC as well. It's often overlooked by those of us who think the LBS is just magic.

Your brakes would seem to be responding normally. The Linked Brake System is complicated but separate from your ABS (which has no effect in your test scenario). If I got any of that wrong you'll know shortly. You're not the only one still learning!




Ain't that the truth. But of the MDT it probably has the most factual information.
 

jfheath

John Heath
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So I spooned on tires, rear pads, new rear bearings. I just for a joke wanted to spin the wheels and check out the brakes. On the center stand, I leaned the bike on front tire. Spun the rear with my hand and squeezed the front brake. Nothing. Put the bike on the rear and spun the front and hit the rear brake, the front tire stopped. I have ABS. Is this normal in a no run standing position? Or regardless, the front brake should have stopped the rear to when I spun it? No engine running, just standing/sitting, nothing on. I should have tried to search for this one, but I don't think I would have posed the right words to do a search for it. Still learning this bike.
There's plenty of good stuff on here about the braking system - but since you ask a question that is more to do with the behaviour, I'll put a brief summary in this post. David (Annas Dad) has posted his detailed information on each of the components - which is excellent. Other stuff you will find in the articles section.

When the bike is in the garage - stationary, on its centre stand - perhaps with a jack under the sump to raise the front wheel slightly:

1) Apply the front brake lever.

Both front brakes grab the two front disk rotors. The front wheel cannot be turned. If the front wheel isn't spinning, there is no effect on the rear brake. The front brake lever applies pressure to the two outer pistons of both front calipers equally.

2)Apply the rear brake pedal.

The rear pedal applies pressure directly to the rear caliper centre piston.
The rear pedal also applied pressure the front caliper centre pistons. The pressure is moderated by the delay valve, which allows the front left centre piston to be applied first. Increasing the pressure on the pedal allows the front right centre piston to be applied subsequently.
With the bike in the garage like this, the pressure from the rear pedal flows from the front left caliper, through the secondary master cylinder (which is part of the front left caliper bracket) and to the two outer pistons of the rear caliper.

The pressure on this line is moderated by the proportional control valve - this ensures that as the pressure applied from the rear brake pedal increases beyond a certain point, the pressure on the rear pads decreases. Yes really. This is necessary when the bike is moving due to the effect of the Secondary Master Cylinder (SMC). See 3 below.

3 The secondary master cylinder (SMC). When the bike is on the open road:

This is activated as a result of the front left caliper grabbing the disc rotor when the bike is moving. This will happen when the front brake lever is applied (activating the to front outer pistons), and also when the rear brake pedal is applied (activating the front left centre piston). In both cases, the SMC is activated, which acts like a second brake lever, and applies pressure to the rear two outer pistons, via the proportional control valve (PCV). The PCV ensure that under heavy braking, the effect of the SMC does not apply too much pressure to the rear brakes, which could result in a lockup on the rear wheel.

4 The ABS

Detects the presence of a lockup in either wheel separately, and momentarily reduces the pressure in the brake lines to the corresponding caliper, before then re-applying it. Repeatedly and very quickly.

General

If the piston in any of the 3 master cylinders is not able to return to its original state, then the pressure in the brake line cannot be relieved, and brakes drag. This problem rarely occurs in the front or rear master cylinder, but due to its position on the front wheel and the angle at which it is positioned, the SMC on the 1300 seems to be more inclined to this type of issue. Regular and thorough change of fluid and bleeding is required to prevent the build up of old fluid, sludge and crud. I do mine every year. It should not be left longer than 2 years, due to the rate at which brake fluid is able to absorb water.
 
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