Rear brake Problem

[Guest ratchethack]

I imagine it is not published because it is a 'trade secret' rather than not being interesting. 

Yeah, it occured to me that it may be a liability consideration. Frickin' lawyers again...

While you cannot use a compound to get an accurate estimation of brake fluid, at least this will put you at the upper limit of expansion.

I believe this is incorrect, if I remember my Physics and P-Chem. In fact, you may have a compound made up of two or more pure fluids, each or all of which alone have a HIGHER CoE than the combined material.

[jrt]

Weird- the website is cutting off my posts. Hell, there's no way I post stuff as long as you do Ratchet, lol.

 

 

 

Here's three patents to look in:

Katz, Donald L.; Esterer, Arnulf K. Hydraulic pressure fluid. (1945), US 2390258

[jrt]

my Physics and P-Chem.  In fact, you may have a compound made up of two or more pure fluids, each or all of which alone have a HIGHER CoE than the combined material. 

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yeah, that's probably true- it's a colligative effect. Neither of the molecules particlarly likes the other one, so you get weird thermodynamics out of the deal.

[Guest ratchethack]

Weird- the website is cutting off my posts.  Hell, there's no way I post stuff as long as you do Ratchet, lol.

Here's three patents to look in:

Katz, Donald L.; Esterer, Arnulf K.  Hydraulic pressure fluid.    (1945),     US  2390258

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Ack! Frickin' PATENT Lawyers.....

 

This is all the same kinda stuff I found myself wading through ad nauseum - but still no CoE. You ain't suggesting CoE can be derived from this, Jason?!

[jrt]

No, I was hoping it would be included in the patent. I didn't think '40s or '50s patents would be that dense, but it won't be the first time I'm naive. I'll do some more searches at work tomorrow where I have access to University databases. Uh, I'll try tomorrow. I might go for a ride instead since it's supposed to be nice.

 

BTW- I'm sorry I hijacked this thread.

[dlaing]

Dave - I can't imagine how heat in and of itself could score rotors?  All brakes function by converting kinetic enerty into thermal energy.  Not all rotors get scored....

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I don't know.

I always assumed scoring was from sand and or dust and or mettalic pads.

But I googled and read a few brake FAQs and they lightly touched on heat as being the culprit.

However I have seen blue disks that were not scored and scored disks that were not blue.

It is true that all disks get hot when braking, and not all get scored, but it is also obvious that how hot they get, varies.

If your pistons are sticking, your pads and rotors will heat up more.

I find it easy to believe that this will, at the very least, increase the risk of scoring, if not cause the scoring.

Has the argument of the day "turned" from global warming to disk heating?

[bigbikerrick]

Rick, I think many of your questions are answered in the link that Dave provided above.  I've gotta post quickly and pick this up later if necessary.

 

OK, now it's time for a little mea culpa .  Dave, I had been searching for the thread you linked in post #3 above, but couldn't find it.  Thanks for posting it.  There's some good stuff there in the little debate we had. 

 

Now here's where I "come clean".  After this debate, I went to a clinical laboratory liquidator and bought a couple of flasks, pipettes, and small stuff and disappeared into the "laboratory" with an industrial thermometer with the intention of accurately graphing out and calculating the CoE of brake fluid.  What happened was unexpected:

 

1.  It was clear that brake fluid DOES in fact expand with heat.  

 

2.  My industrial thermometer only worked within a tiny operating range before it froze up.  It's apparently junk now, and I never found a replacement, so I couldn't proceed with my study.   

 

So PETE WAS RIGHT, and I WAS APPARENTLY WRONG (wot? - no surprise?! ) about the CoE of brake fluid, but I STILL have no way to quantify it.  From what I was able to observe, it isn't LARGE, but it isn't as infinitessimally small as I had suspected, either.

 

Pete's points about the operation of the relief port are important to understand.  Clearly, if you rest your foot at all on the brake lever, you're just begging for trouble.  No getting around Pete's point there.  You stand a better chance of keeping that relief port open with a few mm of free play than with less.  He also said that the CoE of BF is irrelevant, and I've come to agree.  As long as the relief port is functioning and stays operational after the most strenuous heat cycle of one braking application, the CoE is for the most part moot.

 

Now - I've been riding probably 10K miles with next to ZERO free play in my brake lever with NO brake dragging and NO other kinds of symptoms.  Is this significant?  Maybe, maybe not, depending on the attention a rider pays to overall brake system condition, adjustment, and riding habits.  I know many guys who don't have a clue how much play they have in their rear brake, and don't care, since they "don't use it very much."  Well, neither do I, relative to the fronts, but I always pay pretty close attention to my brakes and keep them in good operating order.  I reckon if you aren't sure about the accumulation of the BIG THREE in your brakes (air, water, and caked-on crud 'twixt the pistons and calipers - see link Dave posted above) you oughta have a few mm of free play as Pete suggested.  Me, I'm pretty sure.   Since I ride with the balls of my feet on the pegs, I've eliminated one of the foremost (IMHO) potential initiators of the heat/drag cycle (riding with the relief port closed from unintentional pressure on the brake lever).  I'll continue to do what I've been doing (tight, to the point of ZERO free play) and keep a close eye on it.   IMHO, it has much superior feel this way, y'see, and therefore I get better control...  

 

Dave - I can't imagine how heat in and of itself could score rotors?  All brakes function by converting kinetic enerty into thermal energy.  Not all rotors get scored....

 

Rick - the pads are identical, but once you use them, they take on a directional wear pattern and they should always be re-installed the same way they came out.

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Ratchet, Once again you hit the proverbial nail on the head! I serviced my caliper as you suggested and when bleeding it upside down with the nipple on top ,a large amount of air bubbles came out of the caliper. everything is bolted back together now and NO MORE DRAG : the brake feels much more solid also,as expected. If you ever come to southeastern arizona to ride the sweet roads here, The cervezas are on me,mi Amigo.

[docc]

I've looked back through this thread and just can't find any posts on the 'relief port.' Must be in another thread. What's the skinny?

 

Even with free play, the pedal weight pushes the rod up into contact. I remember one rider who rigged a spring to keep a gap.

[Guest ratchethack]

I've looked back through this thread and just can't find any posts on the 'relief port.' Must be in another thread. What's the skinny?

 

Even with free play, the pedal weight pushes the rod up into contact. I remember one rider who rigged a spring to keep a gap.

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Docc, there's some "inspired" but "partially off-base" discussion (on my part, for which I have fully confessed and repented above) in the thread at the link Dave provided in post #3 in this thread. Pete Roper had weighed in to set me straight (key on the word, "poppycock!" in his post ) with some commentary that included a reference to the operation of the relief port - see post #23 in that thread.

 

The relief port allows any built up "resting pressure" within the brake line - most likely due to expanded air or water vapor displacing the brake fluid - to equalize through the port into the reservoir. The relief port is normally open until the brake lever begins its travel when pressed, at which point it closes. During normal operation, the relief port will open that pressure to ambient as soon as the brake lever returns to its resting position after braking and "re-set" the internal pressure of the brake line so the pads won't drag. But if you ride with your foot resting on the brake lever, or if there's something wrong with the linkage or if there's an obstruction, this could keep the relief port closed.

 

As Pete suggested, in the unlikely event the brake was adjusted so that the lever can't return to it's resting point and open the relief port, or if there's a problem with the linkage or something blocking the relief port, a scenario is likewise conceivable whereby that pressure is not relieved and therefore builds up. In this scenario, that pressure could easily cause the pads to drag, starting the heat/drag cycle, and eventually lock the brake.

 

EDIT: The brake's designed so the weight of the brake lever is far less than sufficient to overcome the spring in the master cylinder. IMHO, it's unlikely that the spring would break or wear out, so there shouldn't be any need for concern about this.

[dlaing]

I've looked back through this thread and just can't find any posts on the 'relief port.' Must be in another thread. What's the skinny?

 

Even with free play, the pedal weight pushes the rod up into contact. I remember one rider who rigged a spring to keep a gap.

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The spring inside the master cylinder SHOULD push the piston past the relief port.

Grunge on the piston cylinder or a worn spring may impede the important feature of a relief port.

If the freeplay is zero, or positive, fluid expansion should push the piston to the relief port if the spring failed to(kind of a natural safety feature).

However, if the fluid boils, all bets are off as it may lock faster than the relief port can let out the fluid. Which is the cruxt of Ratchet's argument, that keeping water and air out of the lines, through frequent fluid replacement, is the most important thing you can do

If the freeplay is substantially NEGATIVE, it would prevent the piston from retreating past the relief port when the fluid expands. This expansion will push the pads against the break causing more heat, more expansion and deadly brake lock.

EDIT good morning I see Ratchet already answered.

[docc]

I so appreciate you guys reposting all of that. No question the rear caliper on the V11 requires a good periodic clean and bleed.

 

At one point there was ( inconclusive ) debate about the proximity of the line to the exhaust crossover. What's the current thinking? Would it benefit from an insulating sleeve?

[Guest ratchethack]

Por nada, mi compadre. IMHO, it couldn't hurt to sleeve the line, but the probability that it's any problem to begin with is slim to zip.

 

BAA, TJM, & YMMV

[dlaing]

At one point there was ( inconclusive ) debate about the proximity of the line to the exhaust crossover. What's the current thinking? Would it benefit from an insulating sleeve?

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I missed that debate.

I am much more concerned about someone forgetting to rehook the line so that it does not drop on the exhaust system.

But an insulating sleeve might protect it from such negligence.

 

And for my pet peeve of the day, those cheap welded on tabs that bend to hold on the rear brake are CHEESEY !