CBS causing me problems

[ewganhoff]

I think the linked brakes on the PCX are an accident waiting to happen.

I'll start by mentioning that I've been riding for 15 years and have had/ridden many bikes big and small from 50cc twist and go through 600 sport bikes to GSX1400. I have never had as many front wheel lock ups while riding in the wet as I do on the PCX.

I am still on the original tyres which are really crap in the wet, but that can't be the whole reason why the front has locked so many times while braking in a straight line.

I'm not Rossi, but I do like to ride by feel, and I do like to break quite hard in the wet while keeping within the limits that I'm expecting. This method has never caused me any trouble before, but with the PCX the front can just go with no warning and I think I've figured out what the problem is.

On a PCX, the front brake works 2 of the pistons in the front calliper and the back brake lever works the rear drum and the 3rd piston in the front calliper. I think this system is robbing me of feel at the front brake lever and to me, that's a very bad thing, especially in the wet.

The other "feature" of the linked brakes that could be adding to the problem is that there is an intensional time delay (correct me if this is not true) between the back brake lever being pulled and the 3rd piston actuating. This means that when I pull the brakes to a point that I think the tyres/conditions can handle I initially get the braking force I was asking for, but after a short time delay the 3rd piston in the front actuates WITH NO EXTRA PRESSURE AT THE LEVER! This means that the front is suddenly asking for more braking force than the tyres/conditions can handle.

I know I'm used to riding much bigger/faster stuff and this is only meant to be a commuter scooter, but I want to be able to ride it in the same style. I know how much braking force I want, but this system seems to give me more than I asked for, which I think is dangerous.

Another problem is that, while riding in crappy conditions like ice or snow, I've learnt to use an intentional rear wheel skid to help me determine the available traction. I can't do that either.

Has anyone unlinked the brakes?

[maddiedog]

Unlinking the brakes isn't too difficult if you're mechanically inclined. The CBS system has a relatively complicated sets of interlinks. Your best option would likely be to bypass the entire subassembly and replace the entire brake cable. (Honda part 43510-KWN-671 / #10 from the BRAKE MASTER CYLINDER (CBS) page of the microfiche is the subassembly you'd bypass). If you want to take this path, I can post up pages from the microfiche here. Note that you will have to disassemble basically the entire bike to get behind the headlight to properly run the new brake cable. You'd really have to buy a service manual to do that, or be very comfortable with taking tupperware off of bikes.

As for the "feature" of a time delay, that actually doesn't exist. The engagement time of the front / rear is entirely linked to how tight the cable for the rear brake is. Nothing more, nothing less. Put your bike up on the centerstand. Look underneath, to the left of the back wheel. See the drum brake actuator? The brake line is hooked in with an a circular nut that you can tighten. I keep mine as tight as it can go without binding on the wheel, so I get almost 100% rear brake out of my CBS unless I'm really braking hard. Try that, it will help some.

Oh, and welcome to the forums!

[dustin91]

That nut also helps adjust the brake lock, which as far as I know not *one* person uses!

[mikelx5]

i only to park on a hill

[gn2]

There's a really simple fix, stop riding like a dick.

[you you]

There's a really simple fix, stop riding like a dick.

I'm with gn2 on this. Most riders with your experience generally ride more smoothly and use the brakes less in the wet

Especially on a teeny scooter

[ewganhoff]

Cheers for the reply, Maddie, I've been lurking for about a year so I know some of the main protagonists on here. OK, so there is no time delay, I'm not sure where I got that from, but at least it's not part of the problem. Unlinking the brakes does sound like too much of a pain in the butt. What would happen if I took the 3rd piston brake line off the calliper and blanked off the hose and the calliper? Would it effect the rear brake, or the front? I know I would lose the use of the third piston but the front brake is strong enough when only the front brake lever is applied.

I'll try tightening the cable down at the drum actuator, maybe it's looser than I thought. What determines the force applied to the 3rd piston's master cylinder and how does the cable interact with it? If, for example, I completely undid the cable down at the drum actuator, would the 3rd piston still work when the back brake lever is pulled?

gn2 and you you, I take your points, this isn't a problem if I'm pottering along and braking very gently, but the fact remains that my slightly aggressive braking style has worked on every other bike in the wet. And I don't mean that I'm braking as hard as I do in the dry, I'd be on my arse at the first puddle, but on other bikes I can brake to a point where I don't think I should brake any harder and hold that force on the levers. With the PCX the front has tried to tuck on me way before I think I'm near the limit, which makes me think that it's the linked brakes that are not letting me get a proper feel for the grip available or the force I'm applying to the brake pads.

gn2, nice to see that you didn't treat me any differently just because we're neighbours!

[gn2]

The CBS is reported to have a rear 70/30 front split on the braking effort.
If you use the CBS alone you can't lock the front first unless there's ice or diesel etc.
You just need to take time to adjust to the different braking system.
The technique I used on the PCX was to use the left lever and only add right lever if necessary.
Not saying this is the correct way, but it worked for me over 18,000 miles with zero lock-ups in all weathers.

[you you]

Cheers for the reply, Maddie, I've been lurking for about a year so I know some of the main protagonists on here. OK, so there is no time delay, I'm not sure where I got that from, but at least it's not part of the problem. Unlinking the brakes does sound like too much of a pain in the butt. What would happen if I took the 3rd piston brake line off the calliper and blanked off the hose and the calliper? Would it effect the rear brake, or the front? I know I would lose the use of the third piston but the front brake is strong enough when only the front brake lever is applied.

I'll try tightening the cable down at the drum actuator, maybe it's looser than I thought. What determines the force applied to the 3rd piston's master cylinder and how does the cable interact with it? If, for example, I completely undid the cable down at the drum actuator, would the 3rd piston still work when the back brake lever is pulled?

gn2 and you you, I take your points, this isn't a problem if I'm pottering along and braking very gently, but the fact remains that my slightly aggressive braking style has worked on every other bike in the wet. And I don't mean that I'm braking as hard as I do in the dry, I'd be on my arse at the first puddle, but on other bikes I can brake to a point where I don't think I should brake any harder and hold that force on the levers. With the PCX the front has tried to tuck on me way before I think I'm near the limit, which makes me think that it's the linked brakes that are not letting me get a proper feel for the grip available or the force I'm applying to the brake pads.

gn2, nice to see that you didn't treat me any differently just because we're neighbours!

Still think the answer is to ride more smoothly in the wet. It's less macho but nobody will know except you.

[gn2]

I aim to not use the brakes other than for when I have to come to a stop.

[you you]

I aim to not use the brakes other than for when I have to come to a stop.

I hate stopping. If I'm out for a ride why do I want to stop. It's expensive enough to go.

[dasshreddar]

To give your combo brake less "front" you need to loosen the adjuster screw at the cbs, then tighten the adjuster at the rear wheel.
I loosened mine about 2 turns, and I would say mine is about 15% front 85% rear, instead of the stock 30-70ish% split.

[ewganhoff]

Using just the rear lever doesn't provide nearly enough retardation for my liking. I have read about, and tried, the "don't use the brakes to slow down, use the throttle" style of riding but I get bored after about 30 seconds. Not dissing it, it works for some people, but it's not what I'm into when I'm on two wheels.

I understand that it is me that is the problem, and that riding more gently will mostly alleviate the issue, but I'm still pissed off that I've been forced to by this bike and it's always been good on others.

To me, this system is more dangerous in the wet than non-linked brakes. Honda might have added safety for someone with no experience or someone who's just happy to take it easy all the time, but they have removed some(maybe a lot) of the control that many riders would be capable of exploiting.

[ewganhoff]

Dasshreddar, I'll give it a try, I would welcome any improvement.

[PKrellner]

That nut also helps adjust the brake lock, which as far as I know not *one* person uses!

Brake lock?

Yeah, I know it's there and I did try it once but it does not work.

Why put it on the bike if it's worthless?

[dasshreddar]

Dasshreddar, I'll give it a try, I would welcome any improvement.

You should be able to get no front brake if you keep loosening the cbs screw...
Or just remove the cbs and get a new longer rear cable.

I think just a rear cable brake is kind of weak, that is why I chose to keep the cbs...
I would personally remove the cbs, if there was a easy rear disc solution for the PCX.

[maddiedog]

Cheers for the reply, Maddie, I've been lurking for about a year so I know some of the main protagonists on here.

I'll save GN2 the usual PM asking him to be nice then. As usual, he has a bit of a point though. Regardless, that's unproductive to the issue we're discussing.

What would happen if I took the 3rd piston brake line off the calliper and blanked off the hose and the calliper? Would it effect the rear brake, or the front? I know I would lose the use of the third piston but the front brake is strong enough when only the front brake lever is applied.

I see no reason that wouldn't work. The CBS has a separate master cylinder, so I don't think the front brake would be adversely affected.

What determines the force applied to the 3rd piston's master cylinder and how does the cable interact with it? If, for example, I completely undid the cable down at the drum actuator, would the 3rd piston still work when the back brake lever is pulled?

In the CBS assembly, you pull on the lever from the handlebar and it simultaneously pulls the rear brake line and engages the brakes by pressurizing the master cylinder. I'm going off the microfiche (I don't have my bike disassembled), but from what I can tell, it doesn't look adjustable. It does appear as though undoing the drum actuator would still engage the front brake though.

I did notice the spring that actuates the piston in the master cylinder is referred to as a "delay spring," which is where I'm guessing you got the delay concept from. It's non-adjustable, whatever it is.

Here's a diagram from Honda showing the two systems are separate hydraulically, which should support the idea of blanking off the hose/caliper, although I don't think that's necessarily the path of least resistance.

cbs.PNG (93.58 KiB) Viewed 4169 times

I think your path of least resistance may be to just drain all the hydraulic fluid from the CBS. It'll effectively do the same thing. Note if you try this and I'm wrong -- which has happened before, you're doing experimentation here, you'll have to take apart at least your windshield and the meter cover below it to access the CBS master cylinder to rebleed that system. If that happens, I'll happily post up the pages outlining that procedure for you. That would be considered "fair use" and not violate copyright. My theory: Draining out the hydraulic fluid from the CBS bleed valve through the front caliper should completely disable the front brake on the combi brake lever, with absolutely no effect on the front brake lever's functionality.

Evidence to support my theory:
1. The service manual explicitly states two separate routines for bleeding the CBS and the main front brake. This implies the systems are discrete.
2. The line from the adjuster (in this how-to) has an almost-direct passthrough to the rear brake. There is a lever in the CBS assembly that appears to actually give greater mechanical advantage to the rear brake than you do at the lever. I've shown this below in a very professional-looking mspaint diagram:

combi.PNG (153.49 KiB) Viewed 4169 times

Proceed at your own risk, and report back if you attempt this.

[Mgalutia88]

Two quick points ewganhoff.
First, the IRC tires from what i hear really give poor traction in dry and wet on both the pcx and the cbr 250r. The alternate Donlop TT 900 tires seem to be great (my pcx 150 came with them). I have NEVER had the front tire skid and I ordered aftermarket pads and shoes for more braking force if you get my drift.

Second, what if you tied the two sides of the front caliper together with a jumper line? straight across the caliper? Try it with a rubber line and then fab up a hard line? Many auto parts stores can make lines in store, or you could always visit a hydraulic shop and see if someone wants to make something for you.

[gn2]

Its worth bearing in mind that adjusting the CBS splitter to reduce the split to the front does not transfer the lost braking effort to the rear, so instead of going from 70/30 to say 85/15 you actually only get 70/15.
Draining the centre pot would have a worse effect.
You would be reducing your overall available braking effort and increasing stopping distance.

[maddiedog]

Its worth bearing in mind that adjusting the CBS splitter to reduce the split to the front does not transfer the lost braking effort to the rear, so instead of going from 70/30 to say 85/15 you actually only get 70/15.
Draining the centre pot would have a worse effect.
You would be reducing your overall available braking effort and increasing stopping distance.

How can you adjust the center splitter though? I see nothing about that in the service manual.

You'll only increase stopping distance if you can't lock with the front caliper only. You can.