rear disc makes noise, not bearing right?

[Guest ratchethack]

For anyone who either didn't follow, didn't buy my argument , won't read boring posts of more than a few paragraphs in length, or simply didn't care (see above), I humbly submit exhibit A (scroll down at link below for photo of heat-annihilated rear brake disk). I would especially call your attention to the comment, "my back wheel locked up on the highway". Evidently, Enzo doesn't quite get it either:

 

http://p209.ezboard.com/ftherollingcrowmot...icID=1418.topic

[Martin Barrett]

won't read boring posts  of more than a few paragraphs in length

 

Yeah, but Enzo has a nice flowery article with pictures as well

[dlaing]

For anyone who either didn't follow, didn't buy my argument , won't read boring posts   of more than a few paragraphs in length, or simply didn't care (see above),

Heh, I guess I bought your argument.

I just posted to http://www.v11lemans.com/forums/index.php?showtopic=5695&hl=

that I did not think that the lever clearance was the reason for his brake lockup.

But my money is still on a sticky piston, although water in the fluid is a close second place...perhaps even a combination of the two.

Glad Enzo did not crash and get hurt.

People, please don't procrastinate on the brake service!

There have been a few rear end lockups whether by brake or bearing.

[Guest ratchethack]

I thought I'd already beaten this one to death, but today somehow I find there's nothing quite like the sheer joy of another maniacal flogging of the proverbial dead horse.

 

I figure it's impossible to know, at any given time, with 100% certainty, that you've got ALL the air, and/or ALL the water out of any brake system. In fact, there's probably always at least a trace of each in there, no matter how surgically clean and thorough you are with your bleeding regimen. Next, as soon as you use the brakes the first time after thorough cleaning, you've got an accumulation (however small) of brake dust trapped between the caliper and the pistons. If allowed, it'll happily grow into a dense, malignant, semi-solid mass. Similarly, because brake fluid is powerfully hygroscopic, drawing water out of the air RIGHT THROUGH the plastic fluid reservior and flexible brake lines (!), both water and air, including water vapor (from the water) have a magical way of accumulating in brake systems over time, never diminishing.

 

If you're following me so far, it's an easy step to conclude that some combination of the 3 - air, water, and crud - is always at work, conspiring against proper operation of the rear brake by trying to induce those pads to drag, just dying to initiate the heat cycle that can seize your brake. Now by pro-actively taking the probabilities of significant accumulation of each of "THE BIG THREE" down to low levels on some kind of a regular basis, my opinion is that you're more'n likely about as safe as safe gets, and for all practical purposes, you can be free of any concern. That's where I like to be.

 

Now be honest and ask yourself this: How many riders (yourself for example ) - or any dealers, for that matter, on behalf of a rider - do you think pay much attention to any two, or even one of the 3, let alone ALL 3? I now (thankfully I'm sure! ) rest my case.

 

A good check of the state of "THE BIG THREE" is to feel the edge of your rear disk after a long ride, where you're not on the brakes for long stretches. If it's hotter than the fronts, it might be high time for a go at it.

 

BTW - I like next to ZERO free play in my rear brake lever. As long as I've maintained my rear brake per above at every tire change, it hasn't given a hint of drag, not even the telltale "backup groan". . I find the fronts don't need even half the attention that the rear seems to require, but then that's just me, and of course and as always, YMMV.

 

Ride safe

[dlaing]

There are apparently two types of freeplay, lever freeplay and activation freeplay.

I suspect you are saying that you have zero lever freeplay.

The critical freeplay is activation freeplay.

What is the measured difference between these two, I don't know.

Heck, I have never measured activation freeplay.

It does not really matter what the difference between the measurements is, as long as they engineered some difference into the master cylinder.

Now I do believe you are fine if you set the freeplay to zero lever movement, but I think it is reinsuring to know that their is some lever freeplay, just a mm or two, to guarantee that we have activation freeplay.

If you have zero activation freeplay or less, the caliber pistons cannot ease back any further than the master cylinder allows it, so if you get heat, you will get expansion of the air in the system and it will try to push the master cylinder back, and if it can't go back to the positive freeplay, where the valve is open for fluid return, than the caliber pistons will push the pads in to the rotors, the heat will get greater, the pressure will get greater, the pistons will push even harder on the pads against the rotor, the rear will lock, you may crash, and you may die.

So, I suggest you have some lever freeplay, so that you can be sure you are safe.

And as Ratchet suggested, SERVICE the brakes or DIE! He did say something like that, right?

[Guest ratchethack]

as Ratchet suggested, SERVICE the brakes or DIE! He did say something like that, right?

57438[/snapback]

As I recall, in one of my previous meandering diatribes on the subject, I suggested something to the effect that unless the root causes of rear brake dragging are well understood, somebody's gonna wind up in a ditch at a time and place not of their own choosing... As first my Pal, LeMans Dan, then Guido, and now Enzo (just to name the ones I know about) have very evidently all come so close to fully demonstrating.

 

It took me nearly 10K miles on my own bike a year ago to come to the point where I had an understanding that care and feeding of the V11 rear brake for practical safety purposes wasn't quite the same as with any machine I've ever owned.

 

At first, I was incredulous that it couldn't be bled properly without taking the caliper off the swingarm. Next came the discovery (before I realized the requirement for stepped-up attention to regular cleaning and proper bleeding) that the rear disk seemed to be abnormally hot after extended rides - much hotter than the fronts - and that I was going through rear pads too quickly and noticing too rapid wear of the disk. After that came the realization that on top of all of this, I think because of the position of the caliper under the swingarm, that it tends to accumulate caliper piston-jamming crud at an unusually rapid rate. NOTE: All of this was observed maintaining at least 2mm free-play at the lever.

 

My last significant realization was that the "backup groan" is a wake-up call. I now think of the groan or squeal as a cry for attention to the causes - and not for action that only temporarily relieves the symptoms (increasing the free play at the lever)...This, my friends, I maintain is exactly what will put you or the next guy in the ditch.

 

In summary, attempting to cut through all my wordy analysis and now 2 year-long discovery process, I'd say that:

 

1. The V11 rear brake requires special attention exceeding that required by most other motorcycle rear brakes. This is due both to it's high susceptability to accumulation of brake dust and crud, and the fact that it can't be bled properly using bleeding procedures that work just fine with most other motorcycles. Someone posted a bleeding procedure that calls for leaving the caliper on the bike and pressing the pistons all the way back in their bores to get "virtually" all the air and water out. Now it may just be me, but I'm not happy with "virtually" safe brakes. I find that taking the caliper off isn't much of a chore, (you've got to get it off to get the crud out anyway!), and I'm far more confident knowing with certainty that it's been bled with the bleeder nipple pointing UP, and at least ALL the air is OUT.

 

2. I maintain that because the V11 rear brake is abnormally sensitive to conspiratorial attack by "THE BIG THREE" (air, water, and accumulated crud), it's at the very least UNWISE to rely solely on adding free play at the lever as a "solution". I consider this false insurance. I've demonstrated, at least to my own satisfaction, that no amount of added free play at the lever is atonement enough for neglect of a proper defense against the THE BIG THREE (the root causes). With THE BIG THREE out of consideration, I've been confident with next to ZERO free play at the lever - and no symptoms whatsoever.

 

There now. Have I finally made a coherent point without stepping on my own foot (- err...brake)?!

[dlaing]

There now.  Have I finally made a coherent point without stepping on my own foot (- err...brake)?!

57469[/snapback]

Bravo!

...and yah, I'll agree that you are fine with NEAR zero freeplay. Especially since you are the mechanic/rider.

But for me, I want a visibly noticeable amount of freeplay. Just a couple millimeters...and not used as a band-aid for a ruptured artery, as you pointed out.

On a somewhat related issue, this article is manadatory reading:

http://www.guzzitech.com/V11S-BrakeLosspic-Patrick.html

[pete roper]

Re: expansion of brake fluid, I'd offer one important correction to what you've stated - it's not expanding brake fluid that causes the brakes to drag.  The coefficient of heat expansion of brake fluid is imperceptably small, by careful design - for the exact purpose of preventing heat-induced drag in hydraulic brakes.  Brake fluid is also designed to have a boiling point that's as high as possible for the same reason. 

50634[/snapback]

 

 

Sorry, but that's complete poppycock! Of course brake fluid will expand when heated. The reason why a brake will drag when it's not being applied is either because the pedal or linkage is adjusted in such a way that the master cylinder piston can't return to the end of it's stroke so the relief port is still closed while the brake is not in use or else the relief port is blocked by something else, although this is fairly rare as the pressures built up inside the system will be fairly high if the brake is dragging and heating the fluid and that will tend to pop out any blockage. If the brake lever/linkages are adjusted right the piston will return to the beginning of it's stroke so the port is open. That being the case the system can't pressurise as any expansion of the fluid, either by heat applied to itself or by the vaporisation of any H2O that has been absorbed into it, simply bleeds back into the reservoir via the relief port.

 

Your other points about the accumulation of crud and the importance of bleeding the system fully are more than valid and correct but I'm afraid you've got a bit confused on that one.

 

One of the major problems with the brakes on almost all *modern* bikes, be they Brembos or Nissin/Tocikos is that the wretched pistins don't come with dust/crud seals that work! If you look at the old O8 callipers they have a heffty and substantial dust seal and these rarely seize up if bled properly and regularly. All the newer calipers seem to have next to nothing in the way of crud-excluders and the buggers seize up at the drop of a hat, especially if you're unlucky enough to live in a place where they put salt on the roads in winter. What makes this particularly vexatious with Brembos is that the company refuses to sell rebuild kits to the great unwashed public due to concerns about litigation! This means that if your calipers seize you have to buy new ones!!!!!! Having said that I think the V11's use an O5 on the back don't they? In which case you probably can get rebuild kits and they *may* still have a decent seal. Any-which-way they still require more care than some due to their stupid location as you mention.

 

Pete

[Guest ratchethack]

Hey Pete - so I'm off base, eh? Well, you're a Pro of formidable credentials and I'm just a piker with some tools in my garage shop and opinions based on my own relatively meager experience, so I'm inclined not to question your point of view. I do, of course, like everyone on this and half a dozen other forums, respect your opinions most highly. But I gotta disagree with you on brake fluid expanding with heat.

 

Admittedly lacking a career in mechanics or direct racing experience, my reasoning is all I have to go on here. I reckon I understand the basics of hydraulic brakes pretty well, having been through both automotive and bike brakes from end to end on many of my own vehicles many times over the years. Pretty basic stuff, mostly. To me, logic dictates that if heat could expand brake fluid to any appreciable degree, hydraulic brakes simply wouldn't operate as effectively as they do under the normal range of operating temperatures (including racing), nor would they be anything close to safe either on road or track. My take is that they'd be locking up all the time rather than my impression, which is: not in recent memory (heated to the point of boiling notwithstanding). Now unless I miss my guess, you've sent more'n a few sets of hydraulic brakes rapidly around the bend on more'n a few occasions?? So no doubt your experience trumps mine by a light-year or 2!!

 

So now that I've buttered you up, I'm gonna whiz you off more than dropping an Ambo flyhweel on your sore toe. Would you happen to have access to technical standards data that shows the thermal coefficient of expansion of brake fluid in normal operating ranges? I don't even know where to look for it. I'd sure like to know for certain if you're right. If so, I'll gladly apologize most profusely for questioning The Master, and at that point I'll change my brake setup accordingly, in defiance of my observations. You might at least be able to point me in the right direction on a source for the data?

 

[ducks under keyboard in anticipation of incoming]

[dlaing]

FWIW the reason a thermometer works is because of the thermal expansion of the fluid (mercury or alcohol)

So, yes the brake fluid will expand.

I am pretty sure that the more air in the fluid, the more it will expand, and if there is boiling water in the fluid, the expansion will be fast, possibly too fast for the fluid to pass back into the resevoir.

[pete roper]

Whoa!!!!! Firstly lets cut the crap about 'the master' OK? those who have met me, Keith Baldini for example, will, (I hope!) back me up when I say I have absolutely NO pretensions to being a 'Master' of anything, apart from maybe 'bation'. I was in no way trying to devalue your observations, in fact I thought I was agreeing with most of them!

 

The fact remains that the CofE of brake fluid is to all intents and purposes irrelevant to braking as long as the linkages are adjusted so the relief port opens when the brake is released. If this isn't the case then, as the fluid heats up it will expand and hold the pads in contact with the disc and from there on it's a viscious circle.

 

What will happen with repeated, hard, applications of the brake is that the pads will transfer heat to the pistons and thence to the fluid. As you pointed out an absence of H2O in the system is vital because if the temerature behind the pistons reaches a temerature higher than the boiling point of water at whatever pressure the system is running at the water turns to steam. Water is a liquid and as such is every bit as good as a hydraulic fluid as brake fluid in terms of *transporting pressure*. The problem occurs if the water mollecules become so excited they become a gas. Gasses are compressible, whereas liquids are, (to all intents an purposes!) not. Once you have a gas in the system, be it air or steam, then the pressure you exert in the system spends it's time squishing the gas rather than pressing the pads against the disc and urning the kinetic enery of the bike and rider moving forwards into heat!

 

In real, everyday, terms the problems caused by water in the fluid are far more likely to be related to damage to seals, pistons and the accumulation of crud that looks like oysters than water vaporisation in your brake fluid. Don't believe me? Next time you've been for a good, hard, flog on your bike hop off and grab the CALIPER. Not the disc you silly boy, unless you want blisters to die for But I doubt VERY much you'll find the calipers themselves are too hot to touch.

 

I wholeheartedly agree with your advice on the care and maintenance of the rear brake. I reckon it's a frontbottom of a design, and as I said, the newer calipers aren't designed with longevity in mind All I was trying to do was correct what I saw as an erroneous and confusing statement in an otherwise valid piece.

 

Vis-a-vis data on brake fluid expansion? Stick some in a beaker, mark it's level, stick a thermometer in it and then heat it with a blow-torch! try not to breathe too near it You'll soon see how much it expands with heat, you don't need some bloody chart to work it out! The other thing is of course to remember that the amount of the fluid that will actually be getting hot is very small! It's not a superconductor so anything apart from the few cc's behind the calipers and in the last inch of the hose is going to be completely irrelevant. Unless it actually boils, (Unlikely.) it's not really going to have an expansion issue unless the relief port is blocked. The fact it is built to have a very high boiling point means that this too is not something that is often an issue unless there is something wrong with the braking system or you're planning on doing 140-0MPH stoppies time after time after time in a Nascar!!!!

 

Pete

[Guest ratchethack]

Pete, I'm glad we at least seem to be in full agreement on the importance of proper bleeding of brakes, but of course I'd expect this! Now when you said, "Sorry, but that's complete poppycock!", somehow, I initially got the silly idea that you thought my statements that you quoted, and possibly my entire post as well, were "complete poppycock!" You may or may not have noticed, what with all that butter slathering in my last post, that I hadn't retreated from my position one iota! Well, I'm not gonna do it here either so please accept my apologies in advance for repeating myself where I find it otherwise difficult to reply...

 

The fact remains that the CofE of brake fluid is to all intents and purposes irrelevant to braking as long as the linkages are adjusted so the relief port opens when the brake is released.

Agreed! Now I believe we've come to the crux of a critically important disagreement here! I maintain, as before, and as you've stated here yourself, Pete, (no doubt borne of your long experience), that because the thermal COE of BF is irrelevant to braking, this in itself is an indicator that it's thermal COE is therefore imperceptibly small. Where we seem to differ is that I reckon it's so small that for all practical purposes, in a reasonable state of purity, it's thermal COE may be assumed to be ZERO within normal operating temp ranges - again, by careful design.

 

In order to head off what might be costly and painful mistakes for riders of the venerable V11 , I've been attempting to get the focus off of the "falsely accused" here, and on to the real perpetrators, the root causes of rear brake seizure in our Guzzi's, which I think many have been overlooking (again - what I'm calling THE BIG THREE - air and water in the fluid, and accumulated crud in the caliper). Unless I'm missing the mark completely here, I think that what we have here is a situation where many have already - and will no doubt continue - to attempt to address their rear brake symptoms solely by adjusting more free play into the brake lever. My take is that this will provide only temporary relief, while still leaving them at full risk of brake seizure. I've personally seen freeplay at the lever on these bikes set as loose as an inch - for "expansion safety"!!!! Again, I run virtually NO play at the lever without any symptoms whatsoever.

In real, everyday, terms the problems caused by water in the fluid are far more likely to be related to damage to seals, pistons and the accumulation of crud that looks like oysters than water vaporisation in your brake fluid.

I'm right with you on the longer-term problems caused by water in the fluid also, Pete. Seizure of the rear disk, however, may be somewhat unrelated to the corrosive effects of water, unless neglect of proper bleeding has been allowed to continue for what I reckon might be longer than many on this forum have owned their Guzzi's.

All I was trying to do was correct what I saw as an erroneous and confusing statement in an otherwise valid piece.

Begging your pardon, Pete, but I for one remain unpersuaded re: the thermal expansion of pure brake fluid as a potential root cause of brake seizure. Again, I believe root causes are IMPURE brake fluid, which encompasses 2 (air and water) of what I'm calling THE BIG THREE villians!

Vis-a-vis data on brake fluid expansion? Stick some in a beaker, mark it's level, stick a thermometer in it and then heat it with a blow-torch! try not to breathe too near it   You'll soon see how much it expands with heat, you don't need some bloody chart to work it out!

Having spent some of the most excruciatingly boring and longest hours of my misspent youth in College Physics and Chemistry Labs while my Pals were doing what College kids are suppossed to do (chasing skirts and drinking beer), I believe I know my way around beakers, scientific (valid) v.s non-scientific (invalid) physical measurements, and enough about the application of real-world knowledge gained via experimental data to submit that measuring the volume of temperature-monitored BF in a beaker as you've suggested - sorry - wouldn't be very scientific, though the concept is certainly sound! I'd hypothesize with some confidence, however: Very low (for practical purposes, next to ZERO) significant expansion of pure BF with heat over a normal brake operating temperature range in a properly enclosed flask (properly "bled" free of water and air!) with a fine-gradient graduated pipette attached! If I had access to the necessary apparatus, I expect I'd have credible enough proof inside of 20 minutes. Absent this, I'm relying on my direct experience with brakes.

 

I hacked around the Web again looking for thermal COE of BF without much luck. A few interesting items (that I think support all of my statements fairly well) that were re-stated several ways in several different sources surfaced:

 

1. [Generic brake fluid] "is engineered to have chemical and physical characteristics that do not change as a result of...cooling or heating." and

 

2. "A typical DOT 4 brake fluid has a dry boiling point of 450F right out of the can. A normal brake system annually absorbs 3% of its fluid weight in water, resulting in a reduction of the boiling point to 300F. At the end of year 2, it is very likely that the system absorbs 5% water, bringing the boiling temperature well below 300F."

 

Hmmmm.....May I suggest that "well below 300F" is well within striking distance of "normal" operating temperatures - at the caliper - of both front and rear Guzzi brakes?!

 

But no hard laboratory data on thermal COE of BF was to be found. I'm sure this is because I don't know where to look, but if you'll allow some speculation here, I'd be tempted to throw this finding itself on the pile with the other stuff that suggests that the reason I can't find it is that it isn't important - and therefore, for all practical purposes, it may well be assumed to be imperceptibly small! Now if, on the other hand, it were significant, I'd expect to find the relevant data well publicized. Capiche?

 

Now, as "frontbottom" designs go, (Incidentally, I find this description a propos on several levels! - the brake's location is after all, well - both front and bottom!) this is one of the least interesting of frontbottoms in recent memory - at least for Yours Truly... But more seriously, I think we're onto a real safety issure here. I'm not trying to defend my honor or ego. I'm just after the truth for my own safety and maybe also the safety of others, should I actually manage to flush something out in the course of discussing this that others might also find of value. One of the points I've been trying to illustrate is that being easily misled on this could lead to disastrous consequences, as I believe may already have been demonstrated here recently.

 

Now Dave, when you said,

 

"FWIW the reason a thermometer works is because of the thermal expansion of the fluid (mercury or alcohol) So, yes the brake fluid will expand."

 

Sorry Dave, but you've taken a leap of logic here that breaks the most fundamental rules. The thermal COE of different fluids vary greatly, depending on inherent physical properties. Fluids such as BF may be engineered to exhibit different properties, including thermal COE, as I've previously noted, and as also quoted above. Mercury and alcohol in thermometers certainly expand with heat. It simply doesn't follow from this that therefore all fluids expand with heat. One classic example of inherent physical properties that differ from one fluid to another is illustrated by consideration of the properties of water. Unlike the properties of (as I recall) all other pure liquids, H20 expands when it freezes, while all other pure liquids contract to varying degrees upon reaching the solid state.

 

So, mi Gizzisti, keep yer brake fluid fresh, dry, and free of air. And for God's sake don't believe you're "safe" as long as you've got slop in yer brake lever!

[pete roper]

So, mi Gizzisti, keep yer brake fluid fresh, dry, and free of air.  And for God's sake don't believe you're "safe" as long as you've got slop in yer brake lever!

57548[/snapback]

 

Look, amen to that, but I'm afraid I'll still disagree with your suposition that brake fluid's C of E is so small as to effectively be imperceptible. Why? Well for the simple reason that i've seen MANY bikes over the years that have had all the free play adjusted out of the lever so the master cylinder piston occludes the relief port and the result, (Apart from the obvious one of damage to the braking system.) is that in service, as the brakes do become super-heated the expansion of the fluid WILL cause the pads to lock ever tighter on the discs resulting in loss of performance, (Obviously.) and driveline damage. The thing is that for this to happen the relief port MUST be shut, otherwise the excess volume of fluid caused by expansion will just bleed back through the relief port into the resevoir!

 

Yes, certainly the other factors previously mentioned, the dust, grime and crud that causes caliper pistons to seize can, and will, give similar symptoms, especially on a non floating rotor if one or both of the pistons decides to seize and I'll wholeheartedly agree about the need to bleed early and often!!!! I don't know how many people have actually pulled calipers apart but it is quite common to find all sorts of repulsive looking stuff that seems to simply *manufacture* itself within the brake system! Oysters! False teeth! Clumps of hair! Aardvark smegma! It's disgusting!!!!!

 

Look, I strongly advise people to follow your advice about ensuring that their brakes are well maintained and kept brim-full with nice clean fluid as I would also strongly advise not leaving a HUGE amount of slack in the linkages. As long as the piston in the master cylinder has full stroke and then there is a millimeter or two of free play between the end of the piston and the bell crank, (if fitted.) or the actuating rod that is all that is needed. The piston isn't going to expand more than a couple of mm? How hot would it need to get to do that???????

 

Another thing often overlooked by people is the actual positioning of the pedal itself. Quite often I've seen brakes that seemingly 'Lock on' and the problem turns out to be simply that as the pilot is riding along his foot is pressing on the pedal sufficiently to apply the brake very slightly, Often imperceptibly, but because in doing this the piston in the MC is pushed into such a position that the relief port is closed the rapid heat build up leads to a 'False seizure' which goes away when somebody else rides the bike due to different riding style/smaller feet/whatever but unfortunately it doesn't take much of this sort of abuse to glaze pads and warp rotors!!!!

 

Anyway, I hope you understand that I was not, and never will, intentionally try to give offence or belittle other peoples' contributions. If I see something really daft and dangerous? Yes, I'll say something if nobody else does, but usually there are enough sensible souls out there I don't have to bother. All I was attempting to do here was maintain a robust debate and I hope that no serious offence was taken?

 

Pete

[dlaing]

Now Dave, when you said,

 

"FWIW the reason a thermometer works is because of the thermal expansion of the fluid (mercury or alcohol) So, yes the brake fluid will expand."

 

Sorry Dave, but you've taken a leap of logic here that breaks the most fundamental rules.  The thermal COE of different fluids vary greatly, depending on inherent physical properties.  Fluids such as BF may be engineered to exhibit different properties, including thermal COE, as I've previously noted, and as also quoted above.  Mercury and alcohol in thermometers certainly expand with heat.  It simply doesn't follow from this that therefore all fluids expand with heat.  One classic example of inherent physical properties that differ from one fluid to another is illustrated by consideration of the properties of water.  Unlike the properties of (as I recall) all other pure liquids, H20 expands when it freezes, while all other pure liquids contract to varying degrees upon reaching the solid state.

 

57548[/snapback]

Now John, while you are correct that by itself, you could call my logic faulty, but you missed that I was simply trying to remind you of the fact that all fluids expand when the temperature rises. Ice is not a fluid, so your leap of logic here breaks the most fundamental rules, or in 'Roper Speak' is poppycock!

EDIT I am wrong, water contracts when the temperature rises from 0 to 4 degrees Celcius

Regardless, as far as I know, all other fluids expand when the temperature rises.

EDIT2 wrong again, my chemist girlfriend suggested that liquid helium and liquid benezene may have negative coefficients. (but we are not putting that in our brake lines.)

And as we have pointed out, what is more relevant is brake fluid after just a few months.

I began the statement with an FWIW because if you have freeplay as Pete and I suggest, the thermal expansion is a non-issue, assuming your master cylinder does not stick or seize.

What is more important is the invasion of water and air and other contaminants that lead to sticking pistons and vaporization.

But none the less, if for whatever reason the master cylinder piston does not return to the open position, thermal expansion is significant enough with virgin fluid to be catastrophic. And to top it all off, there is virtually no such thing as virgin fluid.

As you posted some moisture is inevitable and does lower the boiling point significantly.

Again, if the piston does not return to the open position, thermal expansion is more than significant enough with six month old fluid to be catastrophic...and if you live in Seattle, you will be absorbing more moisture than inland than in San Diego.

Moisture and air are an in escapable, but minimizable reality.

What you seem to fail to accept is that freeplay, and recommending freeplay could save lives.

While your setting it to zero lever freeplay is harmless, advocating it may not be a good idea.

I think Enzo may have set his below zero freeplay.

If one sets it to zero freeplay one cannot as easily monitor if the freeplay slips below zero freeplay.

If people do not know that there should be some freeplay, they may just adjust the lever to fit their foot and ride off with less than zero and die after the thermal expansion creeps in, heats up the disk, heats up the fluid, heats up the disk, then the fluid to the boiling point, and then they crash. RIP

I am going to go out to the garage right now and try to measure the difference between lever freeplay and the point that the valve closes.

Be back soon!

[dlaing]

OK, I was too lazy undo the hose from the clips and bring the caliber over to the mastercylinder side, so all I could do was take off my shoe, and depress the lever and push back the pads.

What I could determine was that with zero lever freeplay, the pads were activated perceptibly without any freeplay....sure there could have been a millimeter or so, but very little.

Now this is fine, because it was not until I held the lever down five to ten millimeters,(maybe more or less, I was guestimating my freekin' toe movement) that I reached a point where I could not push the pads back.

But the effort became progressive, not like a toggle switch, but more like shutting a ball valve to stop the flow of water.

 

Ideally, I would like to see a return spring on the lever, or a stiffer spring on the master cylinder.

I could imagine on a bumpy road the lever must hammer at the master cylinder.

Probably no big deal, but it would be nice knowing the lever was not tapping the brake on every pothole.

I suppose an argument for no freeplay is that the lever would develop less momentum when you hit a bump.

Of course I have followed many V11s and never noticed the brake light come on because of bumps in the road.

I have followed riders (not on Guzzis) who rested there foot on the lever as evidenced by the brake light.

 

Also, for what its worth, a bicycle brake fluid, Stendec, says, "• A low coefficient of thermal expansion to reduce system 'pump up'."

Another less authorative site says silicone brake fluid has a higher coefficient than alcohol fluids.

http://www.off-road.com/4x4web/tlcal/v3n1635.htm