Frozen Brake Fluid: Causes and Solutions.

Hello experts,

According to the VW workshop, the seal for the "release bearing with hydraulic actuation" was damaged due to frozen brake fluid, causing the clutch pedal to get stuck against the floor panel. As a result, the ADAC (German automobile association) had to tow my car to the workshop.

The brake fluid leaked onto the clutch disc, which meant I needed a new clutch.

My question:
Can brake fluid with a specific water content/age cause problems in the summer and "freeze" in the winter?

I don't really believe that .

What do you think?

Quote:

Can brake fluid with a specific water content/age cause problems in the summer and "freeze" in the winter?

Why not? But even without that, central defenders don't last forever either.

Hi,
DOT4 brake fluid solidifies at -60°C. Dissolved water increases the temperature, but even at -20°C? That's almost like the mixing ratio of antifreeze. (I'm roughly considering ethylene glycol and the main components of brake fluid as having similar behavior).
What was the specification of the brake fluid, and when was it last changed?
hg
Herbert.

Quote:

Dissolved water increases the temperature, but by -20°?

And what about brake fluid that has dissolved in water?

It is not uncommon for the clutch to be forgotten when changing the gearbox (Brfl).

Hello everyone!

BM wrote:

... It is not uncommon that the clutch is forgotten during a brake pad replacement.

According to my knowledge and the maintenance plan, this is not included.

On my A4 B5, for example, it's extremely difficult to access the clutch bleed valve, which is located right above the clutch bell housing.

Best regards from Munich!

Hi there,

Quote:

And what about dissolved brake fluid in water?

Something like antifreeze.
"Only – brake fluid can't absorb that much water. You would need to create a mixture for that."
hg
Herbert.

Quote:

What was the specification of the brake fluid, and when was it last changed?

I don't know the specification; I last had the brake fluid changed at the workshop about 4.5 years ago.
I'm not sure if the workshop changed *all* of the fluid back then (for both brakes and clutch).

Hi there,
I once tested it out of curiosity with DOT4 brake fluid. This type of brake fluid is typical for our application and was even from VW/Audi.
- Mixture 3:1 brake fluid/water: the mixture remains clear and does not freeze at -22°C; the cold liquid is viscous (observe the movement of air bubbles).
- Mixture of brake fluid and water (1:1 ratio): the mixture is milky white, does not freeze at -22°C, and air bubbles rise in the cold liquid similarly to water.
Conclusion: Even when in use, DOT4 brake fluid does not freeze at our current temperatures.
Apart from that, the extreme mixing ratios shown in the test are simply not achievable with brake fluid in a braking system.
The cause of the defect in the receiver cylinder was therefore located elsewhere.
Waiting 4.5 years for a brake fluid change is quite a long time.
hg
Herbert.

Hello!

Yes, I can confirm that.
I tested this a few years ago because of a discussion in another forum:
Brake fluid: mixed with water in a 1:1 ratio.
Let it cool down in the freezer at -18°C.
Nothing has changed.

Quote:

Therefore, the cause of the defect in the receiver cylinder was located elsewhere.

That's probably the case. I don't know about the central locking mechanisms (haven't disassembled any yet).

However, for example, from the 123 series era, it sometimes happened that freezing occurred outside, between the dust boot and the cylinder boot. This was triggered by even the slightest traces of brake fluid and condensation. The effect was that the pedal would only return hesitantly (in severe frost), requiring multiple attempts before it would function normally again. These cylinders were still "discreetly" designed, making them much more tolerant than today's models, which resemble a water pistol from a carnival fairground rather than the sender/receiver cylinders used in motor vehicles .