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Old 02-10-03, 08:29 PM   #1
EpsilonArmati
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What's the difference between mechanical/fluid disc brakes?

i.e. what are the mechanics of each? Is one better than the other? How do disc brakes work? Why should I not use them in hot weather? Etc.
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Old 02-10-03, 08:35 PM   #2
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I don't knwo all the details by hydro brakes work by flushing oil into a resevior which cause the clamps to close. It is generally considered more powerful and generally has better modulation (the ability to lightly tap brakes). They also have both sides of the caliper that close.

Mechs work via cables that pull on one side of the caliper. That one side moves the brake inwards closing the rotor in between both pads. Avid is the only one worht considering.

As for not using them in hot weather. Huh? I have never heard that. Rotors get exceptionally hot from over use on the mountain which cause some fading. But in reality this takes a lot of riding and consistent braking and doesn't happen that often.
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Old 02-10-03, 08:40 PM   #3
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What Maelstrom said.

Hydro are supposedly more powerful, but you probably won't find yourself needing any more power than mechanicals could give you.
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Old 02-10-03, 10:25 PM   #4
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If you can afford to make the move to hydraulic and you dont mind the extra weight then go for it. If you are on a smaller budget then take a look at the Avid mechanical discs - they are the only mechanicals worth the money. They operate just as rim brakes do via a cable actuated caliper that moves one pad into the rotor which flexes into the opposing pad sandwiching itself in between the two. A hydraulic disc brake works by pushing a column of brake fluid or mineral oil (depending on the brake) through a hose which actuates the pistons in the caliper and moves the brake pads into the rotor from both sides. Hydraulic brakes do not suffer any power loss from the lever to the rotor because hydraulic lines filled with fluid do not suffer from cable stretch or housing compression like mechanical rim or disc brakes do. Hydros are slightly heavier as the brake fluid is heavier than a cable but not by much (depending on your definition of much). Bottom line if you go mechanical, then go Avid. If you go Hydro then I would suggest Maguras of one form or another, they always seem to be more precise feeling and better made than Hayes. They are all gonna stop you, but some will stop you on a dime while others will, well, they wont. As for the hot weather issue, that sounds like BS.

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Old 02-10-03, 11:01 PM   #5
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I personally am not a tremendous fan of discs in general. That being said, I can see where they would be beneficial for some people. It depends on what style of riding you do. If I were to get discs I would either get the Avid mechanicals or the new XTR discs. The XTR setup is about as light as it gets but is only a two piston setup, whereas the XT setup is a 4 piston. From a pure maintenance standpoint (i.e., just bleeding the darn things) XT is much easier to deal with than Hayes. Avid is also coming out with a hydraulic brake soon which may be worth the wait.
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Old 02-10-03, 11:54 PM   #6
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I disagree with shimano brakes being easier to work on than hayes. Shimano brakes are not quite refined yet, they've only been in the disc brake business for about 2-3 years, where Hayes has been at it for about 10-12 years, if my money was on the line as far as Hydros go, I would opt for Hayes, they have those brakes down to a fine science. Mech wise, go with Avids, they are the best Disc Brake for the buck out of the mechs. I would reccomend Hopes or Maguras before Shimano.
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Old 02-11-03, 02:23 PM   #7
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Quote:
Originally posted by danka24
I disagree with shimano brakes being easier to work on than hayes. Shimano brakes are not quite refined yet, they've only been in the disc brake business for about 2-3 years, where Hayes has been at it for about 10-12 years, if my money was on the line as far as Hydros go, I would opt for Hayes, they have those brakes down to a fine science. .
have you had any prior expereience working with both of them?
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Old 02-11-03, 06:30 PM   #8
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I have and I actually prefer working on hayes. Oh well, I guess each person has their idea on what is easier.
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Old 02-12-03, 08:27 AM   #9
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I agree with Danka, I have found Hayes to be easier to bleed and set-up. The XT's seem a bit more finiky (sp?). Magura's aren't too bad to bleed, but I have yet to be able to bleed a set w/o significant fluid loss to the floor!

The Hayes have a bleeder nut similar to those found on your vehicle. Although there is fluid loss, you can attach a hose and catch it in a container. (Less Mess) With the Magura's, you have to remove the set screw completely. During the removal of the bleeder hose and installation of set screw, I always dump some fluid on the ground!

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Old 02-12-03, 09:32 AM   #10
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Significant fluid loss to the floor??!!
I fit a latex tube (the kind they use in hospitals - don't ask and I'll tell you no lies) over the bleed nipple and drain the oil into a clear bottle, preferably sterilised (no contamination of brake fluid - mineral oil). that way you don't need to spill anything on the floor.
Any hobby shop should sell Hydrocarbon compatible tubes for model aircraft engines. These will work fine.
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Old 02-12-03, 09:34 AM   #11
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PS;
I have no experience with other Hydraulic brakes brands outside of Shimano.
However good hydro's are the way to go. The only mechanical brake that is really good is the Avid. They have managed to reduce the cable friction by careful design and also minimise cable strech and housing compression to increase efficiency.
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Old 02-12-03, 09:39 AM   #12
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I fit a latex tube (the kind they use in hospitals - don't ask and I'll tell you no lies) over the bleed nipple and drain the oil into a clear bottle, preferably sterilised (no contamination of brake fluid - mineral oil). that way you don't need to spill anything on the floor.
That's what I mean about the Magura's. There is NO way to catch the fluid. There is a set-screw that must be removed and then a bleeder fitting inserted to bleed them. Upon all air removal, you must unscrew the bleed fitting and reinsert the set-screw. It's messed up! That's why I like Hayes. You can add the hose and drain into a container. Less Mess!

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Old 02-12-03, 09:55 AM   #13
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Here is a good explanation of hydo brakes ;

"Hydraulic disc brakes function in the following way:
a lever operates the master-cylinder, which increases the oil pressure. Oil is transferred from the reservoir, down the flexible pipe, and into the oil-ways of the caliper. This flow of oil pushes the slave pistons, which move forward in their housings and squeeze the brake pads, which have friction material on their inner surfaces, against the disc. The friction material slows the disc, which is rigidly attached to the wheel, and thereby slows the rotational movement of the wheel."

and Mechanical ;

"Mechanical disc brakes system, if compared with the hydraulic disc brakes system, is much easier to be used, in fact the master cylinder, the reservoir, the pipe and the oil are not necessary.
The mechanical disc brakes system functions in the following way:
a lever , through a cable, operates the caliper that pushes the brake pads, which have friction material on their inner surfaces, against the disc. The friction material slows the disc, which is rigidly attached to the wheel, and thereby slows the rotational movement of the wheel."
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Old 02-12-03, 10:27 AM   #14
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Ok I get it now, I did'nt realise that the magura's had no place a bleed tube.
They're still great brakes though.
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Old 02-12-03, 02:32 PM   #15
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sorry for the snotty comment Danka, i just get annoyed when know-it-all newbies come and say things that they dont know jack about just b/c they have a pair of cheap hayes and because of that they're the "best thing since *****"

Aside from that i was just wondering really b/c my bro has XT's(contradiciton i know) and his weren't all that hard to bleed at all and i guess i never really took the time so examine hayes. Where does the oil get inserted into anyway on those things? My Hope's and XT's just have a resovor(sp) on the top and from there you just pump the fluid into the system and close it
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Old 02-12-03, 02:58 PM   #16
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There is a reservoir on the Hayes brakes but it not like a conventional one. It is inside the mount for the lever. There are two very small reseviors on either side of the master cylinder.
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Old 02-12-03, 06:05 PM   #17
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dirtbikedude- in your description of the mechanical disc brakes, wouldn't the friction cause significant heat between the two discs?
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Old 02-12-03, 06:34 PM   #18
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wouldn't the friction cause significant heat between the two discs?
The statement you speak of I got off of a manufacturers site. They are just speaking of the pads and the material on them. They are not constantly rubing the disk. If not set up properly they will drag some but a very slight drag should not affect your braking too much.
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Old 02-14-03, 04:54 PM   #19
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Originally posted by EpsilonArmati
Why should I not use them in hot weather? Etc.
I doubt you could ever use them hard enough and long enough that they'd get so hot as to negatively affect performance. Brake fluid can take some pretty high temps, and the human body probably isn't powerful enough to push a set of mountain bike brakes past their limits (even if you're DH'ing).
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Old 02-14-03, 06:30 PM   #20
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the human body probably isn't powerful enough to push a set of mountain bike brakes past their limits (even if you're DH'ing).
Not true. i know a few riders who allways encounter brake fade. Granted they ride there brakes most of the way down but it is possible to loose performance. But as for air temp affecting them, I have never had a prob even when it is 115f.
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Old 02-15-03, 09:19 PM   #21
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Originally posted by dirtbikedude
i know a few riders who allways encounter brake fade.
Interesting....have they tried Motul 600? The boiling point is claimed to be 600 degrees (F).
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Old 02-15-03, 09:44 PM   #22
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have they tried Motul 600?
No. I usually clean out the system and run DOT 5 but they do not listen and just deal with it. Is the Motul 600 synthetic like DOT 5?
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Old 02-15-03, 09:44 PM   #23
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I have no experience with hydraulic brakes, but my Avid mechanicals work great and I can't imagine the need for the complexity, cost and weight of hydraulics.

As for th comment that Hayes has been making brakes for 10-12 years, it is closer to 100 years than to 10 as Hayes is one of the oldest brakes companies around (that is, of course, unless this is a different Hayes company making brakes for bikes).

Hydraulic brakes work exactly the same on bikes as they do for cars and motorcycles. Brake fluid in nearly incompressable. Thus, a small cylinder at the lever (pedal in a car) has its plunger piston compressed by hand (foot) action. This compresses the fluid into the hose and behind the pucks in the caliper. The only place there is any give is in the motion of the pucks pushing on the pads and, in turn, against the rotor. Very simple, very reliable and very effective. But, can't imagine that it is necessary in any but the most extreme applications as the Avid mechanicals I use are so impressive. Especially in the wet.
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Old 02-15-03, 09:58 PM   #24
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The only thing not touched on yet is that hydros need specific brake levers while mechs can use any V-brake compatible brake levers.

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Old 02-16-03, 09:42 AM   #25
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Quote:
Originally posted by dirtbikedude
Is the Motul 600 synthetic like DOT 5?
Motul 600 is claimed to be 100% synthetic, but once you get into the higher range of brake fluid, I think they all claim to be "synthetic."

However, DOT 5 is NOT compatable with Motul 600 or any fluid rated DOT 4, 5, or 5.1 (glycol-based). DOT 5 is a silicone-based fluid which is easy on paint but doesn't play well with others. Before 5.1 came along, I used DOT 5 in motorcycle brakes but had to be careful to completely flush out the old fluid.


And now for more info than you ever wanted on brake fluid...wet boiling points for various fluids (don't ask me what "wet" or "dry" boiling point means)

DOT 4 - 311 degrees (F)
DOT 5 - 495 degrees (per Bel-Ray label)
DOT 5.1 - 365 degrees
Motul 600 - 421 degrees*

*"dry" boiling point is about 600 degrees, hence the name "600"
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