V. hot brake caliper

[Dan M]

I put a 2# weight on the lever and that closed the piston 1/10 of an inch beyond the force of the brake lever, and I could start to feel the increased force to roll the bike around. I am sure some friction was occurring before the 1/10 inch. I'd be curious how far it needs to go in before the piston is closed, my guess is starts closing at a little more than 1/14 inch and fully closed at about 1/12 inch.

I guess I am the only one that thinks that that girder could get enough rhythmic momentum on a bumpy road to close it that much.

 

 

The master starts to move fluid as soon as the piston is moved. How far it needs to go before braking action is realized, is determined by how far the pistons needs to move to apply pressure to the pads. The square cut seal relaxes when the hydraulic pressure is relieved, pulling the piston back very slightly. The pads always are in contact with the rotors, there is no mechanism to retract them when the caliper piston retracts. There is just no pressure against them. There will always be some heat generated however slight. I wouldn't be concerned by "warm", it doesn't take much drag to become too hot to hold your hand against.

[dlaing]

Well, it couldn't, Dave. That's exactly my point. Without some additional force holding the relief port closed, and beyond this, dragging the pads for some period of time, there's NO WAY ON THIS PLANET that hitting a bump, by itself, could either start, or contribute to the heat/drag cycle, as you've suggested. A more reasonable (and maybe more interesting) question to ask might be: Could hitting a bump by itself have an effect on the movement of the (otherswise unassisted) brake lever strong enough to first overcome the return spring enough to close the relief port at all -- even for an instant??

 

Not as massive as 2 lb., but "it may well be over a kilogram"??!!

 

Um, a kilo is 2.2 lb., Dave.

 

But let's concentrate on your words above, "momentarily activated" and explore this a little, shall we?

 

[. . . sigh . . .] Somebody's just gotta do it. . . whistle:

 

Dave, first let's make every attempt to be reasonable here, please. I'll make my best honest effort, and I'd appreciate the same. You say you've put weight on the end of your brake lever to determine what it would take to close the relief port. That's fine, and I'm willing to take you at your word on this, but I'm not buying anything remotely close to a kilo (depleted uranium is expensive!!) for your speculation as to what BFG added to his lever, and of course you had no way to measure this as you said you did the 2 lbs. it took to overcome the return spring. Now I'm not likely to disassemble my brake and weigh the components for purposes of this argument. However, I b'lieve we can make valid estimates here that point to reasonable conclusions.

 

I've had all these parts in my hands separately more than once for routine service, and I'm pretty confident in saying that the stock brake lever assembly weighs in the neighborhood of a few ounces total. Let's say 3 oz. Some of the weight of the aluminum lever is offset as measured at the end of the lever -- in part -- by aluminum and additional steel linkage parts on the other side of the lever's fulcrum. That is, gravity and increased G-force effects from a "bump" on the forward end of the brake lever is cancelled out, in part, by the weight of the lever assembly components behind the fulcrum. When the lever is depressed off its resting point, this includes the weight of the piston in the master cylinder, which is of course directly linked.

 

As you've pointed out, and further speculating only for purposes of illustration, if BFG had used the aforementioned depleted uranium for his "splint", he may have raised the weight (and mass) of the lever considerably. Somehow I rather think he used mostly aluminum, possibly with a smattering of other premium bodgery materials. So (being generous here) he may have put as much as an additional ounce of weight as measured at the forward end of what (in total) might now weigh as much as a whopping 3 ounces (yes, I'm considering the steel screw that fixes the rubber pedal, and the pedal itself!) Round figures, I'm estimating (again, being quite generous) that BFG has the equivalent of a total of 2 ounces of normal gravity downforce as measured at the end of a lever arm located ahead of the fulcrum that is not offset by the weight of the lever assembly, linkage, and piston on the other side of the fulcrum. I reckon a postal scale under the lever would be just the thing, and this'd be the end of the story.

 

Now then. If you're accurate in your assessment above in saying that 2 lbs. downforce is what it takes to close the relief port, the question now becomes:

 

How many G's of downforce from a "bump" would it take to get 2 oz. downforce to depress the lever enough to overcome 2 lbs. of return spring force and close the relief port?

 

Since 16 ounces = one pound, and we have 2 lbs. to overcome, it would take 16 G's of downforce just to reach a balance. So I reckon it would take 17 G's or so to close the relief port, and based on feel, possibly upwards of an additional 2 lbs, or another 17 G forces beyond this to actually apply enough pressure to get the brake pads to grip the disk even enough to be detectable at the brake caliper, let alone generate any measurable heat and stopping force at all.

 

Now Dave, how well d'you think the V11 Guzzi by itself, weighing in the neighborhood of 550 lbs (round figures), would tolerate hitting a bump of a magnitude that would generate 17 G's? 17 G's would make the Guzzi weigh 9,350 lbs., or 4.7 tons.

 

As a rider, assuming you weigh 200 lbs. (round figures), how well d'you think YOU would tolerate 17 G's? 17 G's would make you weigh 3,400 lb, or 1.7 tons. How well d'you figure you could tolerate this kind of a "bump" without a G-suit? I b'lieve there are some experienced fighter pilots who can briefly tolerate 8 or so G's without blacking out without a G-suit, IIRC. But how about more than DOUBLE that?!

 

The combined weight of Guzzi and rider at 17 G's would be in the neighborhood of 6.4 tons. Setting suspension considerations aside, how well d'you figure the tires would handle this kind of a "bump"? My Metzeler Z6 rear is rated for a max of 716 lbs. and the Z6 front is rated at a max of 520 lbs., for a total vehicle maximum tire capacity of 1,236 lbs., or .6 tons.

 

So wot you've suggested here, Dave, is a "bump" that would overcome the brake return spring of a magnitude -- just enough to close the relief port, mind you -- of 10.6 times the combined maximum load capacity of Metzeler Z6 tires.

 

Now THAT, my friend, is one walloping, horrific and hellacious BUMP! And this doesn't even apply the brakes! To apply the brakes enough to engage the pads, you'd have to DOUBLE THIS!

 

D'you think these numbers support your conclusion? huh2:

 

Well of course not, silly. Why even ask?! More'n likely , of course, you think my numbers are off by at least an order of magnitude!

 

So with the assumption already safely made that I'm wrong, exactly where d'you now suggest that I've made my mistake(s), Dave?

 

Enquiring minds (well, you know). whistle:

Ygahd! that is some heavy shite

As it turns out the calipers toasted before the girder bodge, so it may be a lost issue.

First of all I would estimate the weight of his girder at the toe pressure point to be well over 2 ounces. Without knowing it, this argument is probably a waste of time. But I guess we could go through the possibilites

I estimate that the weight at the toe pressure point is about 7 ounces.

I suspect it POSSIBLY could be as high as 12 ounces, or, POSSIBLY as low as your suggested 2ounces, in which case I would agree that you are correct.

G-Force?

OK, we have got an estimate of a known force that needs to be overcome, 2lbs.

To my estimate it could take as little as 1.5 lbs to cause drag, but let us go with 2lbs to simplify.

Assuming I am correct that this is equivalent to an 8 oz hammer bouncing up and down with your finger underneath, can you really measure the impact of the hammer in G-Force? G-Force is 9.8 m/s². Whether or not 8 oz moves 32 oz is not determined by acceleration, it is determined by momentum, but of course acceleration is relevant.

I can't figure out the math for this, but I did find that if I dropped a spark plug socket on top of the brake lever from somewhere around 18-24 inches it appeared to deflect the lever enough to activate the brake enough to cause friction.

The sparkplug socket might way 4 ounces, does that mean it impacts with 8Gs from only falling ~20 inches?

Can the bouncing girder have that much momentum?

I don't know, but I would not want to find out with a seized up rear end.

Add GuzziJack's spring to BFG's girder and I think BFG will be able to live long and keep us informed of the time for many years to come.

[dlaing]

The master starts to move fluid as soon as the piston is moved. How far it needs to go before braking action is realized, is determined by how far the pistons needs to move to apply pressure to the pads. The square cut seal relaxes when the hydraulic pressure is relieved, pulling the piston back very slightly. The pads always are in contact with the rotors, there is no mechanism to retract them when the caliper piston retracts. There is just no pressure against them. There will always be some heat generated however slight. I wouldn't be concerned by "warm", it doesn't take much drag to become too hot to hold your hand against.

Thanks Dan That is informative and reassuring.

Still after hearing so many problems, I will try to make a more regular habit of making sure it does not get hot.

Keeping an eye on pad thickness is critical as the pads can wear quickly.

[Guest ratchethack]

I can't figure out the math for this, but I did find that if I dropped a spark plug socket on top of the brake lever from somewhere around 18-24 inches it appeared to deflect the lever enough to activate the brake enough to cause friction.

. . .

8 oz hammer bouncing up and down with your finger underneath. . .

 

Dave, may I respectfully yet sincerely submit that dropping things on the brake lever and bouncing a hammer on your finger in an attempt to illustrate anything useful here is wholly unfounded and entirely irrelevant.

 

May I also respectfully yet sincerely submit (Part II) that you could benefit from elementary lessons in Newtonian Physics, my friend.

 

Professors Wiley E. Coyote and B. B. P. Roadrunner conduct demonstrations regularly somewhere in Television Land every day via re-run cartoons. May I particularly recommend the ones with ACME rockets and archimedian levers long enough to launch stuff like boulders the size of a house up to the tops of cliffs of many hundreds of feet in height. And as we all know, wot goes up (well you know). . .

 

There is no amplitude of "bump" on any road anywhere even marginally survivable by either man or machine that can ever, ever, ever have the slightest effect by itself on a properly operating rear brake in the manner that you have suggested. Such a thing will never, ever, ever happen on yours, mine, BFG's, Wiley E. Coyote's, or B. B. P. Roadrunner's rear brakes by way of road bump-induced G-forces.

 

There are SO MANY other things to worry about that actually have a basis in reality, Dave.

 

Put this one away.

 

Please.

 

[dlaing]

 

Put this one away.

 

Please.

 

What aren't you happy that I agreed that if it weighed 2 oz you would be correct?!?

I suppose I could add weights and drive over a bumpy road with someone watching my brake light.

You would think that if BFG made the girder out of 24 ounce claw hammer, that this would be a problem, right? How about a 16 ounce hammer? How about an 8 ounce hammer?

I really don't know for sure what the cutoff point would be.

With your superior knowledge of physics, please tell me what minimum weight would have to be added to the toe to activate the brakes on a bumpy road...

We know for sure a two pound sledge would activate it.

Regardless of the complex physics involved in the bumps, what if the stiction on the master combines with the mass of the girder?

I am sure the mass of the girder would increase the risk of the stiction on the dirty master keeping the brakes activated.

Or is that another one of you impossibilities?

[Guest Nogbad]

What a load of nonsense on both sides.

 

Can't you and Ratch find something worth fighting over. It's like watching Tom and Jerry.

[Guest ratchethack]

. . .please tell me what minimum weight would have to be added to the toe to activate the brakes on a bumpy road...

Dave, I found a postal scale in my workshop cabinet that I'd picked up to use for something else and forgot I had.

 

Coupla things:

 

1. The in situ weight of the stock brake lever at the end is very close to 2 oz., exactly wot I thought.

 

2. It appears that Nog has nothing better to do today than we do:

What a load of nonsense on both sides.

Else he wouldn't be reading this.

 

3. Assuming it takes 4 lbs downforce to actually induce the brake to drag (just an estimate), a bump would have to exert 32 G's force on the stock lever to activate the brakes, per my above post. I b'lieve this kind of gravitational force would cause the human body, and probably the Guzzi chassis too, to be crushed flat as a pancake under it's own weight. I think this is well past the gravitational force on Jupiter many times over. Maybe Nog will look this up for verification.

 

4. If the brake lever weighed 2 pounds as measured at the end, and my assumption on the requisite force to activate the brakes is valid, it would take the force of a 2G impact to momentarily begin to induce brake drag just from the weight of the brake lever. A bump that induced a 2G force would lurch straight past the max load rating limit of Metzeler Z6 tires, and no doubt even further past the point of bottoming suspension front & rear, depending on rider weight and spring rates, of course. But (again) even then, since road bumps aren't sustained forces, the bumps would be causing infinitessimally tiny heat/drag cycle-inducement relative to simply coming to a normal stop and using the rear brake normally on a normal road on the blue planet.

 

5. By way of illustration and comparison, I have a 20 oz. framing hammer that's only 62.5% of 2 pounds. Holding this hammer makes the weight of the entire stock brake lever seem negligible in comparison.

 

6. Now if for some reason you've decided it'd be a good idea to make your 2 oz. brake lever into a 2 pound medieval war bludgeon, and are ALSO apt to ride on roads that deliver a consistent supply of suspension-bottoming bumps, I reckon you might well have even more peculiar propensities than posting this kind o' dreck on July 4, and a dragging rear brake would be the least o' y'er concerns.

 

Have we kicked this horse dead enough yet, or d'you wanna go another round?

[DeBenGuzzi]

I know what 2 ppl are getting for christmas

[dlaing]

 

1. The in situ weight of the stock brake lever at the end is very close to 2 oz., exactly wot I thought.

 

2. It appears that Nog has nothing better to do today than we do:

 

Else he wouldn't be reading this.

 

3. Assuming it takes 4 lbs downforce to actually induce the brake to drag (just an estimate), a bump would have to exert 32 G's force on the stock lever to activate the brakes, per my above post. I b'lieve this kind of gravitational force would cause the human body, and probably the Guzzi chassis too, to be crushed flat as a pancake under it's own weight. I think this is well past the gravitational force on Jupiter many times over. Maybe Nog will look this up for verification.

 

4. If the brake lever weighed 2 pounds as measured at the end, and my assumption on the requisite force to activate the brakes is valid, it would take the force of a 2G impact to momentarily begin to induce brake drag just from the weight of the brake lever. A bump that induced a 2G force would lurch straight past the max load rating limit of Metzeler Z6 tires, and no doubt even further past the point of bottoming suspension front & rear, depending on rider weight and spring rates, of course. But (again) even then, since road bumps aren't sustained forces, the bumps would be causing infinitessimally tiny heat/drag cycle-inducement relative to simply coming to a normal stop and using the rear brake normally on a normal road on the blue planet.

 

5. By way of illustration and comparison, I have a 20 oz. framing hammer that's only 62.5% of 2 pounds. Holding this hammer makes the weight of the entire stock brake lever seem negligible in comparison.

 

6. Now if for some reason you've decided it'd be a good idea to make your 2 oz. brake lever into a 2 pound medieval war bludgeon, and are ALSO apt to ride on roads that deliver a consistent supply of suspension-bottoming bumps, I reckon you might well have even more peculiar propensities than posting this kind o' dreck on July 4, and a dragging rear brake would be the least o' y'er concerns.

 

Have we kicked this horse dead enough yet, or d'you wanna go another round?

1. Sorry I thought we were taking about BF's Girder

2. Nog, we luv yah dude.

3. I estimate 2#, but why beat a dead horse

4. ibid

5. ibid

6. gotta go watch the fire works!

Happy Independence Day!

Bring back Constitutional Rule!

[docc]

The Nuts and Bolts of V11 LeMans.com has been an 'unmoderated' forum for a long time. I'm having trouble keeping track of which threads to avoid.

 

Usually when two posers, err, I meant 'posters' , bat a thread back and forth like badminton, it's a fair indication the rest of us are 'uninvited.'

 

It's high time you guys took your pi&&ing contest somewhere else.

 

Both of you have had much to offer the rest of us poor ba$tard$ trying to keep these funky bikes running. Yet, is there not some sense of reasonable decorum that suggests when 'enough is enough?'

[belfastguzzi]

Wait a minute!

Did the melt down occur before or after the fracture of the lever?

If after, it certainly could have been the result of a bent master cylinder rod or the massive appendage

Good Heavens! Did you adjust the freeplay after all the duct tape and zip ties!??!

Yes....I know

I was hoping that no-one would mention that...

Now the story has just got complicated again.

 

 

But seriously, whatever the cause, the basic thing is that I'm just interested that the caliper can get so hot that plastic melts. I didn't realise this had happened until later, at home, when replacing the pads. However at the time I did notice that oil was baked onto the brake disc and thought, gosh that must have been pretty hot, considering that I wasn't deliberately using the back brake. The oil was coming back from the cracked timing chest cover.

 

The attempt to fix the pedal could have caused the drag that I was unaware of at the time, on that particular long run. Mind you, the pedal wasn't depressed enough to cause the brake light to come on, as in Leafman's interesting example of another meltdown. Jaap was riding behind me most of the way and his observation was the opposite – the brake light wasn't coming on at all. That was because of the damaged microswitch at the front brake lever and all the braking was being done with the front. For that reason I then sometimes used the bodged rear brake lever, not to brake (especially as I could hear the metal grinding then) but just to give a warning brake light.

 

Leafman is right about the unintentional foot pressure on the pedal being another possible cause. Others have admitted to that habit, especially certain people with policemen's feet. I don't ride with my foot that far forward so I'm pretty sure it wasn't the cause here.

 

I suggest you use the appropriate thread.

[dlaing]

The Nuts and Bolts of V11 LeMans.com has been an 'unmoderated' forum for a long time. I'm having trouble keeping track of which threads to avoid.

 

Usually when two posers, err, I meant 'posters' , bat a thread back and forth like badminton, it's a fair indication the rest of us are 'uninvited.'

 

It's high time you guys took your pi&&ing contest somewhere else.

 

Both of you have had much to offer the rest of us poor ba$tard$ trying to keep these funky bikes running. Yet, is there not some sense of reasonable decorum that suggests when 'enough is enough?'

I don't know what to say.

I'd say sorry, but I am not really very sorry.

I'd take it somewhere else, but Nutz and Bolts is where Ratchet and I thrive.

I kind of understand because I find the arguments frustrating too.

But I find it kind of amazing that we are being told to leave the forum when we are not braking forum rules, not discussing politics, and we are typing our fingers to the bone trying to solve technical problems.

By the way, I think I nailed BFGs problem on the head (But it took a second swing of the hammer)

 

What a load of nonsense on both sides.

 

Can't you and Ratch find something worth fighting over. It's like watching Tom and Jerry.

Brake failure is not worth fighting over?

Okay, from now on I'll just tell Ratchet he is right.

[dlaing]

I must say, Ratchethack and Dlaing make a most curious balance of input. Perhaps you two don't want to hear it, but I've been on this forum a while and the effort put forth by your intense postings is most appreciated.

I like the old docc better.

[mike wilson]

we are not braking forum rules

 

ROTFLMAO

[belfastguzzi]

QUOTE(dlaing @ Jul 5 2007, 07:48 AM)

 

not braking forum rules

ROTFLMAO

ROTFLMBumO?