To use DOT 4 or 5.1 brake fluid?

never a GOOD idea to mix..

DOT 3, 4, 5.1 (all glycol based) are "mixable" DOT 5 is NOT ..Silicone fluid is also slightly more compressible than glycol fluid, does not change color to tip the user to its moisture content, and worst of all, neither accepts or disperses moisture, making systems using it more corrosion prone, and requiring much more frequent fluid changes. Silicone brake fluid also lacks glycol fluid's naturally occurring lubricity. DOT 5 brake fluid also absorbs a small amount of air requiring extra care when bleeding the system of air.

..flush it Bro, start with DOT 3, 4, or 5.1 (depending on your boiling point needs) from a fresh, sealed container or your wasting your time, money, and effort

 

I find that sport level riders often put more stress on brakes than aggressive expert plus riders. Good riders will tend to use more front brake, and brake in shorter harder bursts. This minimizes over heating. Many others will drag the rear brake a lot more to continually scrub speed. This will heat the crap out of the rear brake.

 

I've had good luck with Motul RBF600. It's easy to find at places like Mission Motorsports.

http://www.hrpworld.com/index.cfm?form_cat_id=729&action=category

 

deleted

 

I highly doubt the brake fluids on MTB disc brakes reach it's boiling point or anywhere near it. Pads and rotors will glaze and seize before you even reach the fluid's boiling point.

 

No No, they absolutly do reach boiling points. Ever accidently tap your brake rotor after a long decent???? Usually see smoke coming from your flesh.

 

I would venture to say that bicycle brakes can get to these temps. From wiki:

Minimal boiling points for these specifications are as follows:
Boiling point ranges
Dry boiling point Wet boiling point DOT 3 205°C (401°F) 140°C (284°F) DOT 4 230°C (446°F) 155°C (311°F) DOT 5 260°C (500°F) 180°C (356°F) DOT 5.1 270°C (518°F) 191°C (375°F)

When I was a Pizza cook the oven was 550 degrees. The pizza screen burns were about like rotor burns.... Science.

 

I doubt you'd hit the boiling point with either one, but with something as cheap as fluid, combined with something as important as brakes, why not buy the good stuff?

In my track cars, I always used this:

There's more exotic fluids out there, but this always got the job done. The snazzy thing is that they also have ATE Gold, which has the exact same properties, but it's gold in color...it contrasts nicely with the blue fluid making fluid flushes easy since you can see when you've totally flushed the system.

 

Soooo...... I am guessing I am going to have to take my temp gun to the next fontana race then.....Trust me, Mtn bike brakes def get hot enough to reach the boiling point of DOT4...... part of the main reason that Avid and others went to 5.1

 

They very well may...but there are DOT 4 fluids with higher boiling points than DOT 5.1 fluids, so make sure to read the specifications! :bang:

The main difference between DOT 4 and DOT 5.1 is viscosity...5.1 is typically much thinner, which is (imho) a good thing. That, and I'm pretty sure the lower DOT rated fluids are more hygroscopic and so they require more frequent flushes (every 3-4 years or so in a car). That's what I always came to understand anyway.

Most enthusiasts (car or bike) will change their fluid way more often than that anyway, so that's moot. And the boiling point depends more on the fluid itself rather than its DOT rating, so that can be moot as well as there are DOT 4 fluids with higher boiling points than 5.1's. So at that point, it's a matter of viscosity. Most 5.1's seem to be thinner, which can translate to quicker response in both engagement and disengagement. I can't say I feel a difference in a car, but you might in a system as small as a bike brake.

 

Well, I really hate to say it, cause its already been said, if its labelled as 5.1 it has a higher boiling point. It has to to be labeled as 5.1, it has to meet or exceed the specs for 5.1.....

This is coming from the guy with the BA in Automotive.

Here is the part noone realizes....It doesnt matter if its 3 4 or 5.1...It has to be flushed and replaced at teh same intervals.


Oh, and the word everyone is looking for is Hydroscloropic. All glycol brake fluids start absorbing water as soon as you open the container.

Oh yeah, if your car, its every year, two max.....But as most people neglect to do that, I keep plenty of brake work ready in the shop.



P.S. Talking about the Viscosity..... You have to look at how it reacts under pressure, you cannot tell the viscosity by puring it.

 

deleted

 

Interesting, I litterally went and read it out of one of my textbooks I kept to be sure. Looks as if I will be needing to make a call to a certain instructer that ensured an entire class it was something else.

 

Yeah well, that is the rotor. Heat generated by friction. The brake fluids will be warm but not at boiling point.

The paint on your brake calipers will melt away before your DOT 4 fluids start to boil.

 

No real difference other than it's easier to find in motorcycle shops. Either will be less expensive than if purchasing at a bicycle store. The bottom line is use what the brake manufacturer says to use. Don't automatically by "off on" advertising. Brake fluid is cheap buy the best.

 

Lee is correct! I also remember using the term hydrophilic in relation to fluids which have a tendency to attract/absorb water. :-k

We're all so anal retentive with bike maintenance, though, that this probably doesn't matter at all! Those of you with bikes, anyway.

 

I know nobody in their sane mind would read through the link I posted.[/quote]

Uh, I read it more than once lee. Are you saying im crazy?:lol:

 

deleted

 

Heat builds up in the pads, which is dissapated through... The Rotor, and back into the caliper pistons. The rotor gets to displace that heat to the air, the caliper pistons send it to the fluid, the fluid gets to go back and forth in the line, where it further cools, it also gets to dissipate into teh caliper from there. Therfore, the fluid is hotter than the caliper itself, the fluid is going to be near the heat of the rotor.

Basic path of travel there, pads to piston, piston to fluid, fluid to caliper......You'll boil before you melt paint, unless your having a major brake system failure in process<IE piston stuck, rotor is hitting the caliper directly>





Had a long discussion with my former instructor today, he still stands firm on what he put into his book, so much, he is going to fax me the info for proof on monday. Cant argue with not being able to look up what I was taught, means I need to remember it differently. No worries, havent had a day yet since I got my first degree tha I havent been learning something new. It is funny though, that even through proffesional classes, that little things like wording can still be taught wrong. Its all good, everyone needs a bit o humbling from time to time.

 

deleted