Give me a Brake

[Chris09]

So... I love these brakes, I mean don't get me wrong, I still haven't figured them out, but having looked at that entire burnt mess yesterday I thought I'd go out and actually have a look at what I bought and have been blissfully riding for the last year.
Two things; first, I had to see if I had that right splash of coolant on the valve cover since I have added a few ounces of coolant, maybe I need a new brass tee, and second to check my brakes.
I've lost some coolant over my first twenty five hundred kilometers, when I first got the bike there was a very small puddle under it a couple times but nothing since, it seems that my 09 has a drain hose for the water pump weep hole vs earlier versions and I imagine that maybe it's the mech seal, will check after this weekend when I dissemble it, but meanwhile,
I noticed that my left front caliper has less pad thickness than my right; I'm guessing 3/16" plus compared to closer to 1/4" on the right, both discs seem very good with no glazing or grooves.
So... I revisited the brake system information here and relearned that when the pedal is pressed hydraulic pressure from the pedal master cylinder is applied to the rear caliper centre piston and the proportioning valve rear reservoir input port.
The rise in rear reservoir input port pressure channels fluid pressure sequentially to the left front caliper centre piston, and the right front caliper centre piston.
It seems [ or should I say, it sounds like ] that under moderate pedal braking, right front caliper centre piston actuation may not occur.
So... habitual moderate pedal braking might wear out front left caliper pads.
What I don't understand is....
Between left and right caliper actuation, through the operation of the PCV as a strict result of pedal operation, how much rear outer piston actuation occurs [comes into play and when] as a result of SMC actuation of the left caliper?

bit of a typo there, reservoir instead of PCV on some lines, and this is all with no actuation of the lever [front MC]

And then it seems there's a "break away" pressure, where PCV output pressure drops in relation to input pressure, where I guess, you can actually lock up the rear wheel, and still be able to roll the front tire [like you need to do sometimes] when the PCV input pressure decides...
What... It sucks to be you?

I know that by the time you get there, the ABS [if you've got it] will activate and you should never see it, and I know [as obviously Honda does] how useless rear braking other than balance through a ____ storm is when you're hauling down the center of gravity barely within a foot of the handle bars is while you're straight up, but especially while you're braking through the turns you need a better understanding since you can't separate them, wonder if you might be better off without that SCM activation in the twisties.

 

[aniwack]

It sounds like you've got a cracked three way T. Grab a new 16961-MK7-000 and swap it out yourself. It lives on the right side on the line that returns to the radiator from the engine feeds.

 

[Sadlsor]

@Chris09 insofar as braking in turns, it seems you may be overthinking the linked braking / LBS.
There is no evidence that the ST is dangerous in corners. It's a big bike made for sporty touring, but it's not a WBS racing machine, or a race replica.
If you consistently have to brake hard in turns on the streets, I submit you may need to revisit the proper approach speed and proper entry speed.
Yes, you can brake in corners, and the LBS is actually designed (through the aforementioned proportioning valve) to smooth out, or balance, the brakes front to rear if you are hamfisted on the front binders. This should actually reduce the tendency to break loose the rear end.
I get trail braking and all that, and so long as you are smooth with your inputs, your fears or concerns about the perceived disadvantages of the linked braking should not become reality.
We as riders, should always strive for being smooth with the controls, as a matter of practice.
Don't overthink this (braking in turns), it's not a routine problem that needs to be fixed.

 

[Upt' North]

Wot he said, don't brake in turns. It's not big and it's not clever............
Ride and enjoy.
Upt'North.

 

[dduelin]

Just fix the brakes and they are fine for as fast and as late as you choose to trail brake.

 

[SMSW]

It has been my understanding that the contact patch works to keep you upright. If you brake in turns, you are adding another component to the contact patch's job, and said brake force retarding the bikes speed leaves less force to keep you upright. I know some experts talk about braking with the bike leaned over, but those guys are experts, and usually younger (and highly experienced with sliding along on the ground). For the rest of us, braking before the turn, like @Sadlsor described is the best way to go. YMMV, of course.

 

[jfheath]

That's not a bad undserstanding of the system in your post #1 - not quite right, but you have the general gist.

The brake pedal operates the rear centre piston directly. It also operates the front left centre piston without any hinderance, but not so the front right centre piston. The delay valve on the right fork leg, does not allow the front right centre piston to operate until the pressure from the pedal is enough to overcome the force of a spring inside the delay valve. If you don't press hard enough, the front right centre piston doesn't operate at all.

The brake pedal also operates the two outer pistons on the rear caliper as the fluid from the rear reservoir is fed into the Secondary Master Cylinder (SMC) - which is an integral part of the front left caliper bracket - and it is forced past the primary seal of the SMC to activate the rear outer pistons. That is when the bike is not moving.

When the bike is moving, the SMC gets in on the act. As soon as the front left brakes are applied (which happens whether you press the brake pedal or squeeze the front brake lever, the SMC is moved forward as the brake pads grab the rotating front disc. This moves the SMC piston to push fluid to the rear outer pistons. It doesn't matter what the rear pedal is also doing to the two outer pistons - the SMC is going to win out.

In both cases the fluid from the SMC goes through the proportional control valve (PCV) before reaching the rear outer pistons. This is a clever little device, again based on springs, which ensures that the pressure from either the brake pedal or from the SMC or a combination of both can not be allowed to increase beyond a safe limit. In fact, beyond a certain point, as the pressure increases, the pressure to the rear outer pistons actually decreases. Presumably this is to compensate for the fact that with higher braking forces, the weight of the bike moves to the front wheel and the rear wheel is likely to be getting lighter, and more likely to lock up. The Proportional Control Valve (PCV) is located on the right hand side of the frame, underneath the upper tank, just forward of the ignition coil. There is a bleed valve a little further to the rear, just behind the ignition coil, which is sometimes referred to (mistakenly) as the PCV.

Whether the right hand pads wearing down less quickly than the left pads is due to the effect of the delay valve, I don't know. I suppose if you use the brake pedal a lot for slow speed manoeuvring then the right hand front pad will never be used. Me - I hardly ever touch the brake pedal, except to add additional stopping power in an emergency. But I ride so that they don't happen that often. The front brake lever effectively causes all three sets of outer pistons to be applied. In which case I would expect the wear to be even on the front.

But there are other factors. On wet roads in Yorkshire, UK, the left hand side of the road has more muck and abrasive material in it, which gets splashed up into the brake system. The left hand side of the bike always dries dirtier than the right. So the right hand side is using wet and dry sandpaper, the left is using coarse grit.

II take note of what is going on with the pads, and check the pad springs and the movement of the caliper to make sure things can move properly. And replace all the fronts at he same time.
If you don't know what I mean by that last statement, check out Avoiding the Pitfalls for an explanation.

The ABS - actually I cannot remember it every activating except when I have deliberately tested that it is working. That combined braking system seems to be doing an excellent job in keeping the rear from locking up - which I have had on a normally braked ST1100 as the rear end got a tad lighter.

As for how much do the rear brakes get applied by the SMC ? Well the Honda OEM pads are much thicker for the rear, and they always wear out first. But the rear wheel gets all of the road muck kicked up from the front wheel - so coarse grit sandpaper again. Whichever brake you apply the SMC operates - therefore so too does the rear brake. And the movement on the SMC is only about 1mm - there's not much finesse to it. Try lying next to the bike, turning the rear wheel with your foot and operating the SMC - it takes very little effort to stop the rear wheel from moving with a moderate press of the front left caliper bracket. And it releases immediatley the pressure is removed.

That's if it is working correctly.

 

[Chris09]

Thanks for all the help, I was trying to find one of the diagrams I had seen on this site or linked from here before posting for reference, and I forgot about the delay valve entirely. I'll be getting back to those diagrams and rereading John's explanation [thanks again].
My operation of the bike represents 2.5 of the 36 k total and I haven't done any braking through turns probably at all, but I do have a tendency to bring the pedal in progressively after initiating some maybe greater than moderate [lack of a better explanation for not real hard braking] straight line stops.
I didn't look at anything when I bought it so I can't say what the wear conditions were initially, I don't know if that represents my braking habits, the previous owner's, the original purchaser's or some combination, but now I will watch where it all goes from here.
The bike is very clean, SMC operates nice, clevis and boot look great and the general appearance and condition of everything on the bottom and what can be seen through the fairing parts caused me to believe the PO claim that it hasn't seen any rain could be true. All the discs are in exceptional condition, there's no road sand / salt evidence, no marks on the radiator, 33k / 12 years - 2.5k / year average so its plausible. I don't think I've got the result of much difference in abrasive stuff one side over the other vs the rear too much but could be wrong.
It seems with any new bike I like to find where the rear will lock up while braking hard on the front, and then I feel like I know how they'll work, and then they pretty much last forever, but obviously with this system it's a whole different ball game; maybe I just should get in the habbit of sticking to the lever and let the system manage the rest.
But... If you do find yourself wanting to apply a light amount of braking that you know you should have thought about a few degrees of tilt before, you'll want know exactly what to expect. [You meaning me of course].

 

[Chris09]

Realized that I kind of messed up on my loss of coolant explanation there, I was reading of the coolant leak described on another member's post where he found it on the valve cover. It motivated me to take a look in that area on mine. So far can't find anything but I haven't removed any of the fairing, just peeked between the cracks with a mirror and trouble light. I've only added about two ounces or so over my 2.5 k, would like to get a couple more rides not too far from home before I take it all apart. Sounds like that tee should have been a factory recall.

 

[Sadlsor]

It seems with any new bike I like to find where the rear will lock up while braking hard on the front, and then I feel like I know how they'll work, and then they pretty much last forever, but obviously with this system it's a whole different ball game; maybe I just should get in the habbit of sticking to the lever and let the system manage the rest.

When speaking strictly of STRAIGHT-LINE braking, I will have to disagree.
The fact is, it's widely accepted that approximately 70% of our stopping power will come from the front brakes.
It is further accepted that for maximum straight-line braking power, both brakes must be used. (Whether accepted or not, common sense dictates max brakes=max stopping power.)
When you NEED 100% stopping power to avoid a crash, you will revert to habit; i.e., how you ride in practice. It is conceivable that 3 - 5 feet shorter stopping distance can mean the difference between a hit and a near-miss.
The shortest stopping distance will be the result of applying the brakes to the point just before either wheel locks up, or the ABS kicks in. This is called threshold braking, and this is why quick stops should be routinely practiced on your bike. The very best riders practice quick stops regularly.