Brake Fluid Exchange

[willbur]

I believe getting the fluid hot enough throughout the system isn't possible.
If it were hot enough near the wheels, would it be hot enough in the reservoir?
The cooler fluid would probably absorb whatever moisture was expelled from the hot fluid.

Makes sense but observational evidence suggests it must be a vapor at the master cylinder/ reservoir bc "mushy pedal" is experienced, indicating a compressible substance, i.e. a gas (water vapor). Just an idea...

 

[KrisZ]

if you put on your glasses, you will see a tiny vent hole on the top of the fluid reservoir

That is to allow the membrane in the cap to move as the fluid volume changes with temperature and pad wear. And the membrane seals the fluid inside the reservoir. It is a sealed system and any water vapor trapped cannot escape.

 

[eljefino]

What happens when you get your brakes hot enough to boil off the water? And how does this vapor "burp" out of the system? (Hint: it can't.)

We bleed brakes so this doesn't happen.

The only way it "could" happen would be to drain old fluid then somehow, out of the car, "restore" it. This isn't being done in any first world countries.

 

[edyvw]

Got it. But let me explain. Ford engineers visited auto recycling yards and took many samples of brake fluid. Probably the best place to collect brake fluid for moisture testing. Contrary to expectations, they found very little. So.. I'm just sitting here and the thought pops in my head that perhaps no moisture was found bc it boils off as the brakes are used. Hence my comment re brake flush on the go. Just a thought experiment
What has been found is copper leachate from the metal lines that corrode the system (this probably drops off after the first fluid flush) So, by changing out the brake fluid bc of "moisture" one is actually protecting the system from copper corrosion. And that's what i do.

Do you have a link to a study?
Because, for water to evaporate enough to not show anymore in what is supposed to be a brake fluid, it means that the brake fluid itself deteriorated so much that it is not hygroscopic anymore. Anything that resembles brake fluid will still be hygroscopic and, with that, attract moisture.
Copper is a known issue, as well as moisture. There is no need to put it in quotation marks as it is established fact in a similar manner that sun goes out every morning in the east.

 

[edyvw]

Good point- You maybe right. The vapor rises up bc its a gas to the reservoir and "burps" out with brake application. Note that its a gas bc a spongy pedal is felt, meaning it travelled up to the master cylinder/reservoir

Please provide us with a link to an explanation of this because I and hundreds of others who bleed brakes 3-4 times a year due to track demands would love to know about this.
When a vapor pocket is created, your pedal is spongy because gas is compressible. It does not travel to the master cylinder.

 

[willbur]

Please provide us with a link to an explanation of this because I and hundreds of others who bleed brakes 3-4 times a year due to track demands would love to know about this.
When a vapor pocket is created, your pedal is spongy because gas is compressible. It does not travel to the master cylinder.

I have no link. Purely speculation on my part

 

[tblt44]

I replace the fluid in the reservoir periodically between fluid flushes
A turkey baster works real good for fluid removal, just make sure your wife doesn't use it at Thanksgiving

 

[willbur]

Please provide us with a link to an explanation of this because I and hundreds of others who bleed brakes 3-4 times a year due to track demands would love to know about this.
When a vapor pocket is created, your pedal is spongy because gas is compressible. It does not travel to the master cylinder.

Here ya go boss- From perplexity AI search

Yes, water vapor (ed."Moisture") can travel from a brake caliper to the brake fluid reservoir, especially under conditions of high heat and moisture in the brake system, leading to a spongy brake pedal and reduced braking performance.

Seems to explain my "brake flush on the go" conjecture. Satisfies me. I'm done discussing/defending all this. Out

 

[edyvw]

Here ya go boss- hope you can understand, now

es, water vapor can travel from a brake caliper to the brake fluid reservoir, especially under conditions of high heat and moisture in the brake system, leading to a spongy brake pedal and reduced braking performance.

Where is a link to that?
You do understand that gas is compressible and that it does not matter where you have a vapor pocket?

 

[John105]

if you put on your glasses, you will see a tiny vent hole on the top of the fluid reservoir

Yep, Remember 25 years ago when there was a “sealed” automatic transmission? I was always a manual guy but wondered myself if it’s sealed, how would the fluid ever get dirt into it? It’s not really sealed….it has to vent….

P.s. is this thread also debating whether brake fluid is hygroscopic….very strange

 

[willbur]

Where is a link to that?
You do understand that gas is compressible and that it does not matter where you have a vapor pocket?

Dude,. I'm not going to spoon feed you. Look it up- I did. Out

 

[BMWTurboDzl]

Here ya go boss- From perplexity AI search

Yes, water vapor (ed."Moisture") can travel from a brake caliper to the brake fluid reservoir, especially under conditions of high heat and moisture in the brake system, leading to a spongy brake pedal and reduced braking performance.

Seems to explain my "brake flush on the go" conjecture. Satisfies me. I'm done discussing/defending all this. Out

You do know that AI isn't always correct. AI doesn't validate the answers it provides.

 

[Rust_Belt_Pete]

I do not have the crayons nor the patience.

 

[John105]

I replace the fluid in the reservoir periodically between fluid flushes
A turkey baster works real good for fluid removal, just make sure your wife doesn't use it at Thanksgiving

Seriously I tried that but it was tough to eliminate backwash for lack of a better word. This < $10 tool works wonders…..I always rinse with water and let dry since DOT 3 is highly corrosive. I heard DOT 4 is not

https://a.co/d/6kqUCOk

 

[John105]

Please provide us with a link to an explanation of this because I and hundreds of others who bleed brakes 3-4 times a year due to track demands would love to know about this.
When a vapor pocket is created, your pedal is spongy because gas is compressible. It does not travel to the master cylinder.

I believe this assessment is correct and I didn’t read through all of the debate. But it is true that a fluid cannot be compressed whereas a gas can. In other words say a caliper is removed and simply replaced without bleeding. Now air is in the line and when someone steps on the brakes, th e master pushes fluid out and where there’s air it compresses and doesn’t force the caliper pistons out and pedal goes down more than normal.

I do know from having replaced my ABS pump that BMW states one cannot get the air out of the pump without actuating each channel electronically. That is their procedure, and then an entire flush at each caliper follows.

 

[edyvw]

I believe this assessment is correct and I didn’t read through all of the debate. But it is true that a fluid cannot be compressed whereas a gas can. In other words say a caliper is removed and simply replaced without bleeding. Now air is in the line and when someone steps on the brakes, th e master pushes fluid out and where there’s air it compresses and doesn’t force the caliper pistons out and pedal goes down more than normal.

I do know from having replaced my ABS pump that BMW states one cannot get the air out of the pump without actuating each channel electronically. That is their procedure, and then an entire flush at each caliper follows.

Well yeah, the vapor pocket is created where the heat is, calipers. If it starts moving, very fast it would just blend into brake fluid due to much cooler temperatures further away from calipers.

 

[KrisZ]

Yep, Remember 25 years ago when there was a “sealed” automatic transmission? I was always a manual guy but wondered myself if it’s sealed, how would the fluid ever get dirt into it? It’s not really sealed….it has to vent….

P.s. is this thread also debating whether brake fluid is hygroscopic….very strange

I addressed it already in post #22. The brake system is sealed. The cap has a membrane that allows fluid movement without being exposed to the atmosphere.

It’s nothing like a “sealed” transmission.

Edit:
Here is membrane that’s deformed. The cap side is vented and the brake fluid side is sealed. As the fluid level goes down, it pulls down on the membrane and since the cap side is vented, the membrane simply moves with the pressure change. This way, no vacuum is created in the reservoir.

 

[John105]

I addressed it already in post #22. The brake system is sealed. The cap has a membrane that allows fluid movement without being exposed to the atmosphere.

It’s nothing like a “sealed” transmission.

10-4

 

[The Critic]

I don’t think the moisture issue is as prevalent as it once was. Most vehicles never see driving conditions where the fluid gets hot enough to boil.

The bigger issue is component corrosion from degradation of the additive package. For this reason the test strips are a better gauge, imo.

This is 15 months and 10K on OTC, Genuine Toyota Brake Fluid: