Hi
Just wondering if a study has ever been done to see if brake fluid circulates , the hot fluid rising or ?????
It would seem that if it did NOT circulate the fluid in the caliper or wheel cylinder would brake .down because of the heat , and maybe it would be better to bleed the brakes to get "fresh" fluid in the caliper
Any thoughts ........or am I thinking too much :)
Thanks for your thoughts
I’ve heard a mechanic describe the brake calipers as the trash cans of the system. That’s probably why it’s recommended to bleed them about every year or two.
The fluid does nor circulate to my knowledge.
DrBoost said:The fluid does nor circulate to my knowledge.
So if you had Dot 3 in your brake system and added Dot 4 it would not get down to the "working area" or mix and be Dot 3+4 ?
If a fellow were to have some ATE Blue stashed away, this would be interesting to test.
Brake fluid absorbs water from the air. The boiling point drops when this happens - the difference between rated wet and dry boiling points is with only 3% water. And it's exposed to extreme heat at the caliper. When it boils, you get air bubbles and a soft pedal. That's why you need to bleed and flush it fairly often.
Keith Tanner said:Brake fluid absorbs water from the air. The boiling point drops when this happens - the difference between rated wet and dry boiling points is with only 3% water. And it's exposed to extreme heat at the caliper. When it boils, you get air bubbles and a soft pedal. That's why you need to bleed and flush it fairly often.
OK........but does the water get absorbed thru the filler tank or the hoses ?
and if it does NOT circulate how can it get to the calipers to boil ??
ummmmm
I suspect the hoses - being just rubber with no liner I can remember - have a certain degree of permeability. The reservoir is not completely sealed either. So I'm guessing that most of it is via the reservoir but the hoses also contribute somewhat.
Even if there's no actual circulation, brownian motion would eventually mix all the fluid. We're talking months of time here. And I'll bet there is some circulation, if only because you are pumping fluid from the master to the calipers as part of engaging the brakes.
ross2004 said:Here you go: https://pitstopusa.com/i-5072219-dpi-sure-stop-brake-recirculator.html
Huh I knew there were race cars with this kind of system, but I didn't know you could get an off-the-shelf kit for it.
Keith Tanner said:I suspect the hoses - being just rubber with no liner I can remember - have a certain degree of permeability. The reservoir is not completely sealed either. So I'm guessing that most of it is via the reservoir but the hoses also contribute somewhat.
Even if there's no actual circulation, brownian motion would eventually mix all the fluid. We're talking months of time here. And I'll bet there is some circulation, if only because you are pumping fluid from the master to the calipers as part of engaging the brakes.
Exactly- don't confuse circulation with mixing. You will get mixing, even without circulation.
Keith Tanner said:I suspect the hoses - being just rubber with no liner I can remember - have a certain degree of permeability. The reservoir is not completely sealed either. So I'm guessing that most of it is via the reservoir but the hoses also contribute somewhat.
Even if there's no actual circulation, brownian motion would eventually mix all the fluid. We're talking months of time here. And I'll bet there is some circulation, if only because you are pumping fluid from the master to the calipers as part of engaging the brakes.
Keith is right. Rubber hoses and reservoir seal are permeable by water molecules, but not by brake fluid molecules.
At every pad replacement, I use a suction device to remove as much fluid from the reservoir as I can, then I open the caliper bleeders before pushing the pistons back. This gets rid of most of the old fluid. Refill reservoir with new fluid, and leave caliper bleeders open until clean fluid is coming out.
Angry, do you know if teflon-lined stainless hoses would have less permeability and thus offer longer theoretical brake fluid life? This is just curiosity.
In reply to Keith Tanner :
GRM Definitions: “Brownian Motion” - Spontaneous reaction, in a driver’s pants, most frequently occurring when a car’s brake pedal goes to the floor as approaching Turn 1 Sebring at Warp 5.
In reply to Keith Tanner :
i do not.
but your question made me LOL because i'm an engineer with a pretty good command of the mechanics of the English language, and I could hear my 9th grade English teacher's voice asking, "Why do you care about theoretical brake fluid?"
Don't tell my mom, she's an English teacher. Retired, but they never really retire if you know what I mean.
if water is able to get thru the rubber brake lines I guess I will have to make a "cooling jar" with metal lines inside to cool the fluid with water or antifreeze !
I wonder what the Nascar guys did back in the 60s when they were running drum brakes and only had Dot 3 if that..... they had to cool the brakes and fluid somehow !
californiamilleghia said:if water is able to get thru the rubber brake lines I guess I will have to make a "cooling jar" with metal lines inside to cool the fluid with water or antifreeze !
I wonder what the Nascar guys did back in the 60s when they were running drum brakes and only had Dot 3 if that..... they had to cool the brakes and fluid somehow !
these days, a system has to be pretty poorly designed / implemented to boil the fluid, at least in the OE world. Most pads are "NAO" (non-asbestos organic) which are great insulators. Probably only 10% of brake energy goes into the pad, the rest goes into the rotor.
just thinking about the geometry of a drum brake, there's very little path for thermal conduction between the friction material and the wheel cylinder. back in the day, once cars got fast enough to cook their brakes, vented backing plates with ducting became pretty standard for racing. they also had "sintered metallic" linings which provided more stable friction output as temperature increased. HERE.is a pretty informative thread about the early Corvette big (drum) brakes, with pix.
Keith Tanner said:If a fellow were to have some ATE Blue stashed away, this would be interesting to test.
I might know a guy (okay, it's me) that has two un-opened steel cans, 1 Liter each, of ATE Super Blue Racing DOT 4 brake fluid. I was going to put it in my wife's Audi, but never got around to it and we sold the car years ago. My plan is to sit on this stuff another 10 years, then sell it on ebay and buy a new Mercedes with the proceeds.
I've probably got about four of them. When they were pulled from the market, the FM stock had to go somewhere...
1988RedT2 said:Keith Tanner said:If a fellow were to have some ATE Blue stashed away, this would be interesting to test.
I might know a guy (okay, it's me) that has two un-opened steel cans, 1 Liter each, of ATE Super Blue Racing DOT 4 brake fluid. I was going to put it in my wife's Audi, but never got around to it and we sold the car years ago. My plan is to sit on this stuff another 10 years, then sell it on ebay and buy a new Mercedes with the proceeds.
lol.
I've kept a half filled blue can in the garage, but I won't be using it on my car
In reply to AngryCorvair :
That was pretty much it, sintered linings, ducts and leaning on the bumper ahead of you. I read about Mark Donohue showing up to a NASCAR race with discs and getting rear ended because no one else could slow as quickly.
The fluid would largely not be circulating through the system, that would entail mass movement with continuity. Moisture can diffuse through the system and some dirt to some limited degree. You will also have some mixing due to back and forth movement. Different things that affect the fluid will work via different mechanisms at different rates depending on the contaminant. I have had calipers with a lot of dark fluid and clean stuff some way up the line.
British cars are notorious for brake problems because they arent as sealed against moisture as other systems might be. They suggest flushing fluid every year or two, but people rarely do.
is part of the gunk just the internal surface of the rubber hoses wearing away ?
maybe some temp stickers on the brake lines will give an idea how far the heat moves from the brake drums....
californiamilleghia said:DrBoost said:The fluid does nor circulate to my knowledge.
So if you had Dot 3 in your brake system and added Dot 4 it would not get down to the "working area" or mix and be Dot 3+4 ?
As was said, they would mix. With all the agitation of bumpy roads and similar viscosity, they will mix.
Keith Tanner said:If a fellow were to have some ATE Blue stashed away, this would be interesting to test.
Brake fluid absorbs water from the air. The boiling point drops when this happens - the difference between rated wet and dry boiling points is with only 3% water. And it's exposed to extreme heat at the caliper. When it boils, you get air bubbles and a soft pedal. That's why you need to bleed and flush it fairly often.
I just bled Super Blue out of my system. What do you need to know?
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