Flushing Brakes Without First Drain/ Refill Master

[mjoekingz28]

Originally Posted By: jrmason
In vehicles that get serviced regularly or even semi regular there won't be. But in vehicles that don't get serviced there absolutely will be moisture to some degree. I've seen enough rusted caliper pistons to verify this.

Why do you think every manufacturer has a service interval for brake fluid? Degraded brake fluid is no joke, scam, or folley. It is THE most important system on a vehicle and yet it is also one of the most over looked.



Easy there foul mouth........whoa

Ok

I, myself value steering-suspension over braking.

 

[Nate1979]

Originally Posted By: jrmason

http://gmbrakes.org/gm-brakes/gm-brake-theory-brake-fluid/[/URL]

GM uses a long life brake fluid and does not recommend flushing. Not that I agree with them but there is no recommended service interval for brake fluid.

 

[jrmason]

There is no such thing as a lifetime DOT3 fluid. They might not specify an interval but ultimately the responsibility falls on the consumer. Even worse that they use DOT 3 which is bottom of the barrel. Even European vehicles that use synthetic DOT4 have specified service intervals.

Even the "new and improved" fluid GM released in 2014 is still a DOT3 spec.

 

[Vikas]

My point in the initial posting was to question how moisture survives *BURNING HOT* caliper.

 

[riggaz]

Brake fluid is hygroscopic, water will not settle at the bottom of the system. There is air, therefor moisture, being sucked in via the reservoir as well and this is distributed throughout the system.

If the moisture only settled at the lowest points on the car then when you tested the fluid in the reservoir it would always come up as brand new on the tester. This is not the case.

 

[jrmason]

Most of the moisture in a brake system comes from all the heat cycles. Repeated heating and cooling cycles (especially such large temp swings) in any system will create small amounts of condensation. That's why the fluid always looks worse in the calipers than anywhere else in the system.

 

[riggaz]

Condensation is the change of the physical state of matter from gas phase into liquid phase, and is the reverse of evaporation. Mostly refers to the water cycle.

There is no gas in brake fluid so no condensation can occur.

 

[HangFire]

Originally Posted By: Vikas
My point in the initial posting was to question how moisture survives *BURNING HOT* caliper.


It boils and then condensates. While gaseous you will get a spongy pedal feel.

Many people don't experience this because a.) they never check their fluid level, so it picks up less atmospheric moisture, and b.) they don't race down mountains, so the rare times things get hot enough to cause a problem, they're already stopped and won't be heating up their calipers any more as they inch along in the traffic jam.

 

[stchman]

Originally Posted By: jrmason
There is no such thing as a lifetime DOT3 fluid. They might not specify an interval but ultimately the responsibility falls on the consumer. Even worse that they use DOT 3 which is bottom of the barrel. Even European vehicles that use synthetic DOT4 have specified service intervals.

Even the "new and improved" fluid GM released in 2014 is still a DOT3 spec.


The common misconception is that DOT 4 is a "better" brake fluid than DOT 3. DOT 4 is not better fluid, it simply has a higher boiling point. It is not as though when one puts DOT 4 fluid in a braking system they all the sudden have track ready brakes.

Here is a table of brake fluid boiling points:

________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_260 °C (500 °F)_________180 °C (356 °F)

As you can see DOT 4 boiling point isn't that much higher than DOT 3.

Also it is not as though all DOT 4 brake fluid is better manufactured.

With this being said, the price difference between DOT 3 and DOT 4 fluid is minimal so if you can get the better boiling point for essentially free, great.

 

[Vikas]

I understand it boiling. I don't understand condensation. You do not believe that water vapor escapes from the reservoir cap? The cap does not seemed to be designed to take any pressure from inside. I do not believe the water vapor stick around for the brake fluid to cool down. They are out of there!

 

[HangFire]

Originally Posted By: Vikas
I understand it boiling. I don't understand condensation. You do not believe that water vapor escapes from the reservoir cap? The cap does not seemed to be designed to take any pressure from inside. I do not believe the water vapor stick around for the brake fluid to cool down. They are out of there!


Maybe. It's a long road from the caliper, where it is boiling, to the reservoir.

 

[SOHCman]

Originally Posted By: Vikas
I understand it boiling. I don't understand condensation. You do not believe that water vapor escapes from the reservoir cap? The cap does not seemed to be designed to take any pressure from inside. I do not believe the water vapor stick around for the brake fluid to cool down. They are out of there!


Vikas, the reason the condensation/moisture/water sticks around is that THE NATURE OF BRAKE FLUID is HYDROSCOPIC (spelling?) meaning that it absorbs moisture...............

There is no escaping from the reservoir cap, its not like a cup of water sitting on the counter waiting to evaporate.

The water is absorbed into the brake fluid because thats what the chemicals like polyglycols and glycol ethers do, they absorb water, period.

cheers!

 

[Brad_C]

Originally Posted By: Vikas
I understand it boiling. I don't understand condensation. You do not believe that water vapor escapes from the reservoir cap?


There is no belief. It doesn't happen. Period. Ever.

When you heat brake fluid past the boiling point it boils. When you cool it below the boiling point it condenses. So you overheat the caliper and some of the fluid boils. Those vapor bubbles start to expand and push fluid out of the cylinder, through the master and back into the reservoir. As the bubbles work their way up toward the pipework they move away from the hot part of the caliper and cool below the boiling point and re-condense. The bubbles never make it anywhere near the master cylinder as they re-condense as soon as they reach any part of the system that is below the boiling point, so you have a little cloud of boiling/condensing fluid in the caliper and lower pipework.

The other thing that happens is as you apply brake pressure you naturally increase the pressure in the system, the increasing pressure raises the boiling point and things start to re-condense. You've already pushed fluid back out of the system, so there is a large void of boiling fluid to fill, which can make the pedal go to the floor as it fills the caliper back up and increases the pressure enough to re-condense the boiling fluid.

The remaining factor is on split braking systems. So you've cooked the front calipers, boiled the fluid and pushed some back into the reservoir. When you hit the brakes your master pumps up both the front and rear, but your rears are not boiling so you get significant resistance on the pedal from the rear brakes, while you don't have enough volume on the front brakes with that limited travel to up the pressure up to an effective level, so you need to pump like mad to get any form of front brakes back.

The lower the amount of water in the system, the less likely all this is to happen.

 

[Vikas]

Good explanation; I appreciate it.

 

[SumpChump]

And here's the whole brake fluid topic in a nutshell...

You brake on the fluid in the calipers and the last 10 inches of line FROM FACTORY FILL the entire life of your car unless you bleed them. That's it.

When I really finally understood that I was a changed man. A few ounces of fluid does ALL the work... all those potential years. The rest of the lines and fluid are just there to compress the last bit at the calipers.... No circulation no refreshing like coolant or oil or gas.

 

[riggaz]

Manufacturers recommend replacing ALL the brake fluid as a rule. Hygroscopic fluid distribute the moisture throughout, it does not stay in the last 10 inches near the caliper.