Topic: SOFT front brake - i'm outta ideas...

[singedebile]

Hot air rises! 
i had a similar experience, and here's what i did. 
i tactically acquired my wifes hairdryer and w/ brake lever tied to handlebar and bars turned to the left,  i gently heated every component of my system.  paying closer attention to any transition, especially the brake light switch and banjo intersections.  i did this every 30 minutes for about 2 hours while i worked on other stuff on my bike. i was pretty surprised at the bubbles still coming out of the MC when i finally pumped it.

i hadnt heard it before ..interesting idea, good thinking!

[Franky]

Hi there

Just wanted to let you know, that the main reason for the poor brake power was the misalignment i spoke of in a previous post.

I messed around with more washers and a bit of bending and it keeps getting better. It's fine for now. I think next winter I'll look into replacing the fork, brakes and all with something more modern.

Thanks for your all your help guys

[Oddjob]

I'm wondering if you've done what I did once and fitted the caliper incorrectly, was before I became a bike mechanic and the 500 was a new model bike back then so it wasn't that easy to find a person who actually knew a great deal about disc brakes on bikes. Anyway I'd installed the mudguard mount behind the caliper pin top mount, this made the caliper sit at an angle in relation to the disc, like yourself I got pressure but very little braking power, this kept getting better as the pad wore down at an angle to match the disc. I spotted it when I took the caliper off one day to check pad wear and started kicking myself for being so stupid, the piston pad was worn at about 30 degrees. Bought new pads, moved the mudguard brace to the outside of the caliper pin top mount and everything was fine afterwards.

[Oddjob]

When I purchased my first CB550, the PO had stripper the bleed nipple so badly that I knew it wouldn’t come out without snapping off in the caliper, but the brakes needed bleeding so I removed the caliper and pumped the lever until the piston was just about to fall out. Then I emptied the master cylinder reservoir and refilled it with fresh fluid before I pushed the caliper piston all the way back in again. You wouldn’t believe how fast the air was purged from the lines. I repeated this procedure a couple more times before remounting the caliper and the system worked perfectly.

It’s very similar to forcing the brake fluid through the bleeder up to the master cylinder, but you don’t need a hypo and there is no fluid spills to contend with.

wow that's really good info I will have to give that ago.  makes allot of sense.

2 problems with that Roach, firstly your supposed to replace brake fluid at least every 2 years, I do mine every year regardless, you need to do this because brake fluid absorbs water, whereas brake fluid has a high boiling point water does not, so water in your fluid is a very BAD idea, if it boils it turns to steam, you can compress steam unlike fluids, so you end up with no brakes. This method would leave unchanged fluid around the piston area where you really don't want it to be.
Secondly you stand a good chance of flipping the master cylinder seal back on itself, if you flip it back it no longer seals against the bore of the cylinder and thus no longer pumps fluid or it partially seals and you get horrible brakes as a result, the seal is designed to push forward thus pushing fluid down the lines, as the fluid comes back up the lines it flexs a little to allow this, as the amount of fluid going down and back it quite low it can cope with this, a large amount like your suggesting will stand a good chance of overpowering it's limited amount of flex thus flipping it back on itself, you can dismantle the MC but TBH who really wants to do that very often if at all.

[tlbranth]

Odd - I agree that brake fluid should be changed regularly and often and I'm probably wrong about this but the Japanese started using that concertina rubber thingy on top of the fluid waaaaaay back to prevent absorbtion of water. It seems to me that water would have a tough time being absorbed into such a system. But the fluid does get funky.

[Oddjob]

Water gets into every hydraulic system regardless of how you try and keep it out. The very hygoscopic nature of hydraulic fluid means it sucks this water up, you can't see it as the fluid absorbs the water. You cannot run the system in a vacuum, even the MC res cap has a breather hole in it, changes in air temp cause condensation to form on the inside of the MC, fluid splashing around inside the MC as your riding draws this condensation into the system. It's a very vicious circle and that's why every motor manufacturer recommends you change the fluid on a periodic basis, just changing half of it doesn't cure the problem, if the fluid around the piston is water saturated then your in big trouble, the first area of the braking system that gets hot is the pad/disc, this transfers into the caliper, very soon the caliper is very hot, try touching one after a run, you don't realise just how much your using the brakes and just how much heat your generating, a hot climate is even worse as the brakes take longer to cool down between each use. Once the caliper gets to a crucial heat level any water in the brake fluid will start to boil, as soon as it does your brake effectiveness will drop off rapidly, when it turns to steam the lever will come back to the handlebar as you'll be compressing the water in it's steam form.
Lastly, what's heavier oil or water? we both know it's water, so the water in the fluid will try to go to the lowest point of the system which will be the caliper/piston area, leaving that crucial area unchanged is a recipe for disaster IMO.
Not trying to preach here, just trying to enlighten members who may not know this and could be hurt or killed by that lack of knowledge

[TwoTired]

Water gets into every hydraulic system regardless of how you try and keep it out. The very hygoscopic nature of hydraulic fluid means it sucks this water up, you can't see it as the fluid absorbs the water.

Agreed.  (With the exception of silicone fluid which is out there, but not recommended by me.)

You cannot run the system in a vacuum, even the MC res cap has a breather hole in it, 

No sir, there is a belows in every MC for bikes I seen; certainly on Hondas.

changes in air temp cause condensation to form on the inside of the MC, fluid splashing around inside the MC as your riding draws this condensation into the system. It's a very vicious circle and that's why every motor manufacturer recommends you change the fluid on a periodic basis, just changing half of it doesn't cure the problem, if the fluid around the piston is water saturated then your in big trouble, the first area of the braking system that gets hot is the pad/disc, this transfers into the caliper, very soon the caliper is very hot, try touching one after a run, you don't realise just how much your using the brakes and just how much heat your generating, a hot climate is even worse as the brakes take longer to cool down between each use. Once the caliper gets to a crucial heat level any water in the brake fluid will start to boil, as soon as it does your brake effectiveness will drop off rapidly, when it turns to steam the lever will come back to the handlebar as you'll be compressing the water in it's steam form.

An interesting theory, for sure.  Water does enter the system through osmosis of and the seal membranes.  Mostly the adverse effect is compromising the corrosion inhibitors.  I don't know of any support for the "steam theory".  But, I would be willing to review test reports or other supportive analysis toward it's validity.

Lastly, what's heavier oil or water? we both know it's water, so the water in the fluid will try to go to the lowest point of the system which will be the caliper/piston area, leaving that crucial area unchanged is a recipe for disaster IMO.

Wait. Oil?  Where did that come from, and how did that get into the brake system?  The scenario you forward is only true for Silicone brake fluid.  DOT3, 4, and 5.1 all absorb the water and distribute it solution.

Not trying to preach here, just trying to enlighten members who may not know this and could be hurt or killed by that lack of knowledge.

I'm all for enlightenment, and am more than willing to share.  I sure would prefer to enlighten based on reality/factual info, though.

Cheers,

[TwoTired]

Most master cylinders have a bellows to seal the system from air. I've also seen fluid many years old still look like new. If the system is tight no worries about moisture at the master cylinder area. Storing the machine indoors along with fine weather riding is different than leaving the sucker out in the elements and driving in rain. A  blanket statement like you must change your fluid by this date is a bunch of BS. I'd be more concerned with  rubber wear debris contaminating the fluid over a long time. The brake fluid in my car is basically 12 years old and the thing still stops fine. The only fluid exchange happened 7 years ago when I replaced a wheel cylinder and had to bleed the thing. For that matter the coolant is original and being that it has over 250,000k it can self destruct for all I care.

The water can go through the seal membranes via osmosis.  The absorbtion rate is highly related to humidity levels and direct exposure to water contact.

Without testing the fluid to see how much water has been absorbed, you can't know if there is enough water to cause a problem or negate the corrosion inhibitors in the fluid.  So, it is far cheaper to simply change out the fluid periodically.
12 year old fluid may still be ok if it has been in an H2O deprived existence for all that time.  Then again, your brake system will still function with part of the internals corroded.  The point is to prevent that corrosion, especially in more complex ABS systems.

Since I'm on a roll...
I will caution you about engine coolant turning acidic.  I've seen it eat through an aluminum water pump housing in as little as 4 years.

I'm certainly no saint when it come to changing fluids per timetable.  But, I am aware of the possibilities and consequences, and can live with the guilt. 

Cheers,

[tlbranth]

Didn't mean to start a ruckus. I was just sayin'....

[Oddjob]

Water gets into every hydraulic system regardless of how you try and keep it out. The very hygoscopic nature of hydraulic fluid means it sucks this water up, you can't see it as the fluid absorbs the water.

Agreed.  (With the exception of silicone fluid which is out there, but not recommended by me.)

You cannot run the system in a vacuum, even the MC res cap has a breather hole in it, 

No sir, there is a belows in every MC for bikes I seen; certainly on Hondas.
As far as I can recall the master cylinder lid has a small pinprick hole.

changes in air temp cause condensation to form on the inside of the MC, fluid splashing around inside the MC as your riding draws this condensation into the system. It's a very vicious circle and that's why every motor manufacturer recommends you change the fluid on a periodic basis, just changing half of it doesn't cure the problem, if the fluid around the piston is water saturated then your in big trouble, the first area of the braking system that gets hot is the pad/disc, this transfers into the caliper, very soon the caliper is very hot, try touching one after a run, you don't realise just how much your using the brakes and just how much heat your generating, a hot climate is even worse as the brakes take longer to cool down between each use. Once the caliper gets to a crucial heat level any water in the brake fluid will start to boil, as soon as it does your brake effectiveness will drop off rapidly, when it turns to steam the lever will come back to the handlebar as you'll be compressing the water in it's steam form.

An interesting theory, for sure.  Water does enter the system through osmosis of and the seal membranes.  Mostly the adverse effect is compromising the corrosion inhibitors.  I don't know of any support for the "steam theory".  But, I would be willing to review test reports or other supportive analysis toward it's validity.
This is not a theory, literature is out ther on the web confirming that condensation does occur inside an hydraulic system, most components are metal especially the master cylinder, there is air inside the master cylinder, if the metal suddenly goes cold the water suspended inside the air will condense onto the metal, sudden altitude changes can cause this, we've all ridden somewhere where the air has suddenly gone very cold, areas like this will cause condensation to occur.

Lastly, what's heavier oil or water? we both know it's water, so the water in the fluid will try to go to the lowest point of the system which will be the caliper/piston area, leaving that crucial area unchanged is a recipe for disaster IMO.

Wait. Oil?  Where did that come from, and how did that get into the brake system?  The scenario you forward is only true for Silicone brake fluid.  DOT3, 4, and 5.1 all absorb the water and distribute it solution.
Ok poor choice of words but principle still aplies, the water suspended in the fluid will move down the system, gravity causes this. Saturated or contaminated hydraulic fluid boils at a much lower level than fresh fluid, typically at a level of normal braking temperatures, it's documented that old or low quality fluid is also susceptable to boiling at normal braking temps, it's called vapour lock. Don't believe me then google brake vapour lock. Brake fluid is designed to boil in excess of 300c, water as we both know boils at 100c, if water is suspended in the fluid what would boil first? boiling water turns to steam, steam can be compressed, hence vapour lock. 12 year old fluid is not advisable, it may still work but it will be contaminated, we've all seen black brake fluids, black fluid still works though BUT the hotter the brakes get the more chance of vapour lock, you may not drive hard enough to get to this level so you think everything is still fine, however like a ticking bomb it's just waiting for a set of circumstances to happen. Once you've crashed the fluid changes back from a vapour to a liquid making the cause of the accident difficult to determine.

Not trying to preach here, just trying to enlighten members who may not know this and could be hurt or killed by that lack of knowledge.

I'm all for enlightenment, and am more than willing to share.  I sure would prefer to enlighten based on reality/factual info, though.

Cheers,

As I've said google it, there are reams of factual info out there written by people far more enlighted than us, I don't profess to be an expert of brake fluid but I do believe it when the brake fluid experts say things will happen and provide all the evidence to support their theorys.

[Oddjob]

Didn't mean to start a ruckus. I was just sayin'....

LOL it's not a ruckus it's just a discussion and like a lot of discussions sometimes people can get a little OTT. I take no offense, if I'm wrong I'm wrong it's not the end of the world and it won't be the first time.

[Duanob]

I'd like to go back to the OP post about the mis-aligned caliper. Please clarify. The caliper assembly is supposed to pivot. There is an adjustment screw with a spring that you align the caliper pads to the disc for the easiest rotation of the front wheel. Did you adjust that screw?

[Franky]

@Oddjob: You nailed this one! The mudguard was indeed on the wrong side! The PO must have done this, and I didn't notice since it doesn't look wrong at all. Also, when I got the bike and replaced the pads, they were worn in the same way as you described. I swopped the position and got rid of the washers I added and it's OK now. Like you did ages ago, I too kick myself for being so stupid! I was so darn focused on all the bleeding! I even have the 360T sitting next to it with the correct assembly Jeeez!

@Duanob: Yes, tried adjusting the screw and all, but as you can tell from the above; issue solved!

Thanks for all your help and patience guys :-)

BTW: here's a site I keep about my CB550 build. It's in danish, but the dates on the left and pics are for all :-)
http://www.franky.dk/cbriders/?12.05.2011-nyt-saede-laves,86

[Oddjob]

RESULT!!!

It was only when you mentioned about adding washers that I remembered the mudguard problem. It's very easily done if your fitting the caliper mount after you've fitted the mudguard, I'm betting your not the only one on this forum who's experienced this so posting the solution may just prompt other members to check their caliper position.

Glad to help.