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Old 03-10-03, 09:40 PM   #1
dazco
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brake fluid may boil?!

I was reading the downloaded manual for hayes discs (bought some today...don't have em yet) and in one section it talks about the possibility of long downhills causing the brake fluid to get so hot it boils. I ride fireroads a lot and coming back down some of the steep ones i have to brake very hard and very often. They are up to 8 miles, tho most are around 3 or 4.

Is this something i have to worry about? Has anyone had this happen to you, and when it boils what are the results? I weigh around 170 if that matters.

(these d@mn things are looking like more and more trouble the more i read about them)
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Old 03-10-03, 10:25 PM   #2
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Quote:
Originally posted by dazco
when it boils what are the results?
First it depends on what kind of system you have. In a closed system, as the fluid heats up and expands, the brakes may not retract fully once you let the lever go which may cause your brakes to drag. If it expands enough, you'll have inadvertant lockup. Open systems don't have this problem.

Once beyond that, the fluid may boil. When this happens, air pockets are created and the opposite effect happens. Since air is compressible, you will go through the entire lever throw with little to no braking effort applied to the rotor. If you survive the ride, you'll have to then bleed the brakes.
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Old 03-11-03, 12:02 AM   #3
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If you survive the ride, you'll have to then bleed the brakes
Hmmm...... you've painted some pretty horrific pictures in my mind.
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Old 03-11-03, 01:06 AM   #4
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Quote:
Originally posted by dazco
Hmmm...... you've painted some pretty horrific pictures in my mind.
Well, it's sort of the same effect as having your rim brake pads melt. Of course, trailside repairs are easier with rim brakes. Toasting your disc fluid often means walking and the end of the ride. With rim brakes, you can use your multi-tool's knife (you do carry one don't you?) to shave away the glaze and continue on (after letting your rims cool). The advantage to disc brakes however is that they don't build up heat as quickly in the first place. Either way, better riding technique helps... the more you stay off your brakes the greater chance you give them to cool. Periodically stopping to let the rotors or rims cool will also help. It may not seem as "manly" but I'd take people laughing at me over having failed brakes at the edge of a mountain switchback.
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Old 03-11-03, 08:36 AM   #5
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You should be fine as long as you get a set of brakes made for what you want to do. Don't buy Hope Minis and bomb down Pikes Peak...
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Old 03-11-03, 11:39 AM   #6
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brake less and go faster...you should have a problem on regular fire roads like that. They really aren't long enough (unless you CONSTANTLY brake) to worry about it.
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Old 03-11-03, 12:41 PM   #7
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I don't have to brake constantly, but i'd say 70-80% of the time i'm pulling the levers anywhere from med. hard to squeezing the life out of them. This is how at least 2 of my favorite roads are, both about 3 to 4 miles long.
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Old 03-11-03, 01:24 PM   #8
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IF.....and that is a very big IF you could get the fluid to boil...it's not like it would all of a sudden start to, so what I'm saying is that even before the fluid boiled, the brakes would start to get very mushy so you would notice it. It's NOT like they will just all of a sudden work great at one point, then the next time you'll grab brake and have nothing there.
You'll know if the brake fluid is getting to the point or starting to... because even before they get mushy they would fist expand and start to drag, because of the fluid expanding...but on open systems, which hayes are, they still wont lock out on the rotors when the fluid expands. They will drag more then usual... then get mushy becuase the fluid was soo hot and the pads and rotors are exptremely hot.
Remember this is a very BIG what IFFFFF situation!! In my years of racing and riding and being a mech, I've never seen this happen. I've come down from runs and had the brakes hot enough to if you got water on the rotors it would warp them, and also had them hot enough to burn the inside of you leg(be very very careful when you hold you bike)....especially if you hold the tire between your legs for a sec...you'll hit that rotor which will be very very hot!! I've learned from experience... LOL

Long story short...don't worry about it...you'll be fine! If they get soft or don't break as well..then slow down and take a brake, let them cool and get going again(you'll probably not ever have to do that though)

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Old 03-11-03, 03:29 PM   #9
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Thanks 4 that. I figured it was an unlikely senario, but nice to know it's that unlikely. They should be here tonite and i can't wait. I'm anxious to start using them and see just how much of the bad things i hear are true, and how much of it is due to incompetence on the users part. I'm no bike mech, but i'm an electronic tech and i'm good with mechanical things. So i hope to be able to set them up and maintain them correctly. Funny thing is, i keep hearing all these horror stories about discs, yet on the many motorcycles i owned when i was younger i never once had a disc problem. Wouldn't you think there would be MORE problems with a heavy motorcycle than with a bike that weighs a fraction of the weight?
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Old 03-11-03, 03:54 PM   #10
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Good luck with them, let us know what you think when you get em all setup! It's not difficult especially if you're mech. minded. I don't know what problems you've been hearing of, but the hayes I got...went with the comps....the plastic body scared me at first, but I actually like it now, I figure if I hit a tree hard enough to brake it it would probably brake a alloy one too...so this way it's cheaper for me to fix.

The only issue I've seen repetively(probably spelled it wrong) with hayes is on the caliper itself there is a gasket between the two halfs of the caliper that are bolted together. This gasket goes bad after a while, and no matter how many times you bleed the brakes, they'll feel fine for the first two squeezes and then feel mushy again.
The reason that happens is because the gasket leaks, it doesn't let fluid out...it just leaks enough to let air into the system and that is where you get the mushy feeling from. Hayes will take care of that for you if you do ever have that problem...just call em and then they'll have you send the bakes to them for repair.

So far I have not had this issue with mine...and I'm really happy with mine. Again..good luck and I'm sure you'll be happy with them!
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Old 03-11-03, 04:48 PM   #11
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Thats the first i've heard of that one, and i hope theres a reason for that cuz it sounds like a bad one. Mostly i've heard of sqealing and problems that require constant adjustments. The one that worrys me is where a lot of people have said they have to readjust the caliper every time they take the wheel off. I have to remove my wheel every ride because i have no room to store it where it'll fit without removing the front wheel ! But then i guess this problem will quickly turn me into an expert at caliper adjustment.

In any case, i'll post here when i've had a chance to use em. Thanks...
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Old 03-11-03, 05:09 PM   #12
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Quote:
Originally posted by dazco
Funny thing is, i keep hearing all these horror stories about discs, yet on the many motorcycles i owned when i was younger i never once had a disc problem. Wouldn't you think there would be MORE problems with a heavy motorcycle than with a bike that weighs a fraction of the weight?
Just because you don't hear about it doesn't mean it doesn't/can't happen. I have an engineer's mind and when I look at anything I try and envision all sorts of failure modes (some people tell me this is a curse). The likelihood (or lack thereof) of the failures is also something to keep in mind. Some applications push closer to the design limitations than others. Fact of the matter is that discs are more complicated than rim brakes and have a number of additional and different failure modes. As far as automotive discs brakes go, although they work on the same principles, they do incorporate a number of design differences and have the luxury of more sophisticated mechanisms to combat failures because they can be made heavier, bulkier and more complicated without effecting performance (design margin) as much as bicycle disc systems.
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Old 03-11-03, 05:39 PM   #13
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8 mile downhills .... I gotta find me some of those.
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Old 03-11-03, 05:48 PM   #14
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8 mile downhills .... I gotta find me some of those.
Try the Mt. Muller Loop. It's an awesome ride but you suffer badly for the first few miles. You'll have an incredible sense of accomplishment once you make it to the top though. Bring a camera. I forgot mine. Oh well... guess I'll have to do it again this year once things have dried out/warmed up a bit.
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Old 03-11-03, 06:09 PM   #15
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Yes, you can boil the fluid, but have to really try...
At one time I had an early disk brake on the front of my off road tandem. We rode to the top of Skinner Mountain, near North Hampton, Ma. On the way up I marked the road 3/4 of a mile from the gate with bright colored powdered chalk. It would have sucked to run into the gate at speed. On the decent we reached "stupid speed" (58.9 mph) When we passed the chalk mark I started braking. As the fluid heats up it expands, causing the brake pads to drag on the rotor. The pads dragging on the rotors makes more heat, until the fluid boils. The rotor warpped from the heat, so much that it touched the spokes, it had to bend to pass though the brake. The pads melted and the hub had to be repacked due to overheating of the hub. The brake and the brake hose also had to be replaced. In one run I had turned the brake into junk.

Now not to start a flame war, keep in mind this was an early disk brake, and it was mounted on a TANDEM. With better then twice the mass of a single bike, bike and riders 440 lb. That's a lot of energy to scrub off. Disks brakes have gotten better. Oh, "stupid speed" is any speed that makes your stoker swear that she will never get on the bike again.
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Old 03-11-03, 06:17 PM   #16
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Quote:
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Oh, "stupid speed" is any speed that makes your stoker swear that she will never get on the bike again.
For some of us that can be any speed at all. |8^(
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Old 03-11-03, 07:00 PM   #17
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58.9 mph
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Old 03-11-03, 08:27 PM   #18
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Dazco i would not worry at all about the brake fluid heating up. The systems and fluids used now have such high tolerances that it'd take a lot to really get it to heat up to the point where the fluid boils. I doubt it happens at all anymore
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Old 03-11-03, 09:05 PM   #19
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I'm not. I only posted because when i read that in the manual it had me a bit worried with all the hard downhill braking i do. But i suppose they just have to include any possibilities no matter how unlikely.
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Old 03-11-03, 09:07 PM   #20
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I think we need another person to repeat the same thing in here again...what do you all think?

I'm joking guys...ha ha ...

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Old 03-12-03, 08:03 PM   #21
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If your interested.....

Boiling Point
DOT 3 DOT 4 DOT 5 (silicone-based) DOT 5.1 (non-silicone based)
Dry 401F 446F 500F 500F
Wet 284F 311F 365F 365F

Notice how much lower the boiling point is when theres a little water in the fluid.
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