Brake fluid ?

Shocks, Springs, Brakes, Frame, Body Work, etc

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cuslog
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Brake fluid ?

Post by cuslog » Mon May 19, 2014 12:42 pm

So what is it about a braking system that requires specialized "Brake fluid" ?
I hate that damn stuff - so corrosive - feels so slimey on your hands.
An automotive braking system is just hydraulics isn't it ?
Why not use hydraulic fluid ?
Is it just the heat consideration ?
My brake lines aren't near any heat source - I've been careful to route the lines well away.

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Re: Brake fluid ?

Post by Brian P » Mon May 19, 2014 6:08 pm

Needs high temperature resistance but still needs to flow in cold weather. Traditional hydrocarbons that have a high enough boiling point would be practically solid in below-freezing temperature. (The issue isn't just the brake lines ... it's generally the calipers themselves. Heat from the friction pads goes pretty much straight into the caliper pistons. Usually they're made of insulating materials but still, they can get pretty hot.)

Needs to not attack the materials used in seals.

Needs to not contribute to corrosion.

Needs to be as incompressible as possible.

cuslog
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Re: Brake fluid ?

Post by cuslog » Mon May 19, 2014 10:39 pm

Hmmmm, I've run enough heavy equipment - in hot weather and heavy use - hydraulic fluid gets pretty darned hot.
I've run it in -40 degree weather too - it still works.
When does brake fluid get that hot ?
In a drag car, its not like you're driving through the mountains, riding the brakes down a steep incline or road racing where you're hard braking on corner after corner.
Hypothetical question really - I've still got brake fluid in my system - just finished bleeding 4 piston calipers all around - dripping and drooling it all over - hate that stuff.
Seems its just about the heat.

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Re: Brake fluid ?

Post by mystic1582 » Tue May 20, 2014 12:00 am

You answered your own question. Are you stuck on a deserted island and not fluid?
Pour sea water in. It won't compress within reason and it may get you to a safe place.

Are you driving an everyday vehicle that is exposed to hot/cold etc. The caliper pistons move in and out as do the wheel cylinders if it has them.
Do you think brake fluid absorbs moisture and can corrode internal parts?

Perhaps you are driving a circle track car and leaning hard on the brakes. You might hope the boiling temp is sufficient. You know, where the rotor is glowing orange
the caliper has changed color, nasty smells everywhere. Well if you used bargain fluid you will never have gotten to that point. If you used high quality high boiling
point fluid you will still have a pedal and be able to stop.

It's like anything else use the proper tool for the job.

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Re: Brake fluid ?

Post by Brian P » Tue May 20, 2014 6:51 am

cuslog wrote:Hmmmm, I've run enough heavy equipment - in hot weather and heavy use - hydraulic fluid gets pretty darned hot.
I've run it in -40 degree weather too - it still works.
In normal applications, it doesn't reach the advertised boiling temperature of brake fluid, though.
cuslog wrote:When does brake fluid get that hot ?
In a drag car, its not like you're driving through the mountains, riding the brakes down a steep incline or road racing where you're hard braking on corner after corner.
Your original question didn't specify the application. Brake fluid can get that hot in road racing where you're hard braking on corner after corner, or riding the brakes down a steep incline. A drag car barely needs brakes at all. You could probably get away with water and antifreeze in the brake system. That doesn't mean you should - but you could.
cuslog wrote:Hypothetical question really - I've still got brake fluid in my system - just finished bleeding 4 piston calipers all around - dripping and drooling it all over - hate that stuff.
Seems its just about the heat.
Pretty much. Brake system component manufacturers don't necessarily know the details of every specific application that their components will be used for, so it's designed in a standardized manner to work with brake fluid - because that will work in ANY application within reasonable bounds.

Brake fluid is also designed to be hygroscopic so that it gets water droplets out of the system. Hydraulic oil won't do that - the water droplets would stay put - and if they're in a bad spot, like the bottom of one of the calipers, and that caliper gets hot, the water boils and then you have no brakes. Brake fluid is designed to absorb a certain amount of water before the combined boiling temperature of the brake fluid and water mixture goes below acceptable bounds. Hydraulic oil won't do that.

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Re: Brake fluid ?

Post by cuslog » Tue May 20, 2014 10:58 am

Yes, I thought it was probably about the heat - but I thought there might be more to it than that.
I just wish they could make something that wasn't so corrosive to paint.
Seems for a drag car that spending extra $ on "high performance" brake fluid is a waste of money ? For a trailer Queen show car - even more so.

Anybody got a nice method for bleeding brakes without dripping or drooling a single drop ?
I'm using my Mighty Vac with vacuum hose over the bleeder nipple- which works OK but it's still a bit messy.

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Re: Brake fluid ?

Post by Brian P » Tue May 20, 2014 5:56 pm

DOT 5 (not 5.1) brake fluid is silicone based, and won't attack paint.

It is also not hygroscopic and will not draw water out of the system. It also is more compressible.

It is also absolutely, completely, chemically incompatible with standard (DOT 3, 4, or 5.1) brake fluids and will ruin your brake system if mixed, or if even a trace of the old fluid remains. Bad things happen if you either top up a standard brake system with DOT 5, or you top up a DOT 5 filled system with anything else.

I believe Harley-Davidson uses it in at least some models, so you should be able to get it at their dealers, if not elsewhere.

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Re: Brake fluid ?

Post by Jens.J » Thu Jun 05, 2014 7:42 am

Hydraulic oil will destroy all the rubber lines and seals :roll:

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Re: Brake fluid ?

Post by rancherort » Sat Jun 07, 2014 4:13 pm

Brake fluid has very unique properties that make it brake fluid.
1. It's a very viscous fluid and it maintains its viscosity under sever conditions whether it's 110 or 40 below the fluid is exactly the same viscosity.
2. It's a very thermally stable fluid. Meaning it won't breakdown quickly even at its boiling point. Normal hydraulic fluid will start breaking down within minutes if it's at or even near it's boiling point.
3. It carries a rust inhibitor
4. It has to be a very low compression fluid. Meaning that it will only compress under very high pressure. Example if you measure pressure at master cylinder and at the point furthest from the master it will be exactly the same.
5. It has to remain in good shape for years. Most people trade in their vehicle without ever replacing the brake fluid.

So it may be gooey and nasty but that's because it's brake fluid.

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Re: Brake fluid ?

Post by justahoby » Sat Jun 21, 2014 11:22 pm

Jens.J wrote:Hydraulic oil will destroy all the rubber lines and seals :roll:
viscosity of hydraulic oil will make the pedal feel like lead, and be very resistant in lines i immagine
As I'm approaching 40,I still think I'm 20. What the hell is wrong with me?

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Re: Brake fluid ?

Post by Schurkey » Mon Sep 08, 2014 6:31 pm

Thousands of years ago, I remember reading (Motor Trend? Road and Track?) that Rolls-Royce (Bentley, too, no doubt) used "special" rubber in the brake system--piston cups, hoses, caliper sealing rings--and therefore they could use hydraulic oil in the brake reservoir.

This would have been 1970's, maybe 1980's sometime.

I haven't been able to confirm this recently.

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Re: Brake fluid ?

Post by nhrastocker » Tue Sep 09, 2014 12:32 pm

Schurkey wrote:Thousands of years ago, I remember reading (Motor Trend? Road and Track?) that Rolls-Royce (Bentley, too, no doubt) used "special" rubber in the brake system--piston cups, hoses, caliper sealing rings--and therefore they could use hydraulic oil in the brake reservoir.

This would have been 1970's, maybe 1980's sometime.

I haven't been able to confirm this recently.
You are correct.
A friend of mine at one time, put the same hydraulic fluid he used on his private airplane on his car because he believed it would be better and safer.
Drove for two blocks and lost all braking. Very costly test since he ruined all the brake related hydraulic components such as master cylinder, calipers and hoses.

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Re: Brake fluid ?

Post by Rizzle » Sun Sep 14, 2014 7:50 pm

Brake fluid absorbs moisture (hygroscopic). This means that if some moisture finds its way into the system, it does not remain as a pocket of water. In an oil based system (Shimano, and a couple other bicycle brake manufacturers use mineral oil as fluid) if that moisture finds its way near a caliper (considering oil floats on water, this is entirely possible) or any other high source of heat, it can boil, causing the hydraulic system that is brakes to stop functioning due to the gases that have become entrapped in the lines.

Dot 5, as mentioned, can be put in a completely fresh/cleaned brake system with seals designed for dot 3, 4 + 5.1.


If you don't like brake fluid, convert to air brakes. just need to pick up an air brake license.

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Re: Brake fluid ?

Post by winr » Sat Oct 25, 2014 12:26 am

I used silicone based fluid in mu 65 F-100 after convertin to disk brakes.

All new calipers, wheel cylinders, dual master cylinder, brake lines, etc.

After 10 years mu calipers an cylinders were rusty.

I read on several online sites the water that gets in the brake system,
does not absorb into the fluid an drops to the lowest point.



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Re: Brake fluid ?

Post by Calypso » Sun Oct 26, 2014 10:26 am

winr wrote:I used silicone based fluid in mu 65 F-100 after convertin to disk brakes.

All new calipers, wheel cylinders, dual master cylinder, brake lines, etc.

After 10 years mu calipers an cylinders were rusty.

I read on several online sites the water that gets in the brake system,
does not absorb into the fluid an drops to the lowest point.



Ricky.
Did you change the fluid regularly?

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