Bremse lässt sich weit reintreten | Posts 16+

@gremlin:

How can air get into a closed system?
The fluid level was always okay, nothing was done to the braking system during that time, and if air had been drawn in during a fluid change, it wouldn't have become noticeable after 2 years.

@bertil:

I read the freaking manual!
Last change was almost exactly 21 months ago!
I wasn't aware of the differences in quality between different types of brake fluid at that time.

Juergen wrote:

How can air get into a closed system?

Brake fluid is highly hygroscopic, meaning it readily absorbs moisture. Consequently, a certain amount of moisture (water) from the air enters the brake fluid through the ventilation of the reservoir.
At high temperatures, the water boils and air bubbles form. This is how air enters the system.

Please provide the text you would like me to translate from German to English. I need the text to be able to provide a translation.
Because brake fluid absorbs water from the air, its boiling point decreases over time, not based on mileage.
...

Quote:

I read the freaking manual! Last change was almost exactly 21 months ago! I didn't know anything about the quality differences in brake fluid at that time.

Then I would have looked into why the brake fluid needs to be changed every 24 months. You would have quickly realized that air in the braking system can also come from the water that the fluid absorbs over time. Often, such air bubbles can even remain in the system.

I've experienced this firsthand. During a rally with many tight corners and high speeds, meaning a lot of braking force, the brake fluid was about 6 months old, and yet the pedal suddenly went to the floor (air in the system). I managed to get myself to a mandatory break and hoped that the brakes would cool down and work normally again (about 2 hours of break). But I was wrong. The problem was still there.
While bleeding the brakes in the workshop, I found a large amount of air in the system. A boiling point test revealed an extremely low value, meaning the brake fluid was already unusable after only 6 months.

While this is an extreme case, the same thing can happen to a regular street car, although the process is usually much slower.


So, if you're experiencing a problem like this and you only have 3 months left before you need to change the brake fluid anyway, I would advise you to change the brake fluid first.

Hey guys!

Without wanting to cause any headaches, but how's your rear brake doing? If it's also nearing the end of its life (especially with new front pads), it might not be able to adjust properly anymore.

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Without wanting to cause any headaches, but how's your rear brake doing? If it's also nearing the end of its life (especially with new front pads), it might not be able to adjust properly anymore.


*Headaches*

Okay, with all due respect, I'm not completely stupid!

Air or vapor bubbles in the braking system typically manifest as a very soft, spongy brake pedal. Additionally, the braking force on an affected wheel would be weaker, and this would be noticeable by a pulling sensation during braking.

That is not the case for me.

The pedal initially offers normal resistance and then gradually gives way. Furthermore, this effect is the same whether the brakes are cold or hot, which, in turn, makes the vapor bubble theory unlikely.

Everyone who has ever read a repair manual has probably heard about the hygroscopic properties of brake fluid. However, in my 20 years of driving, I have never experienced any problems with it, even though I have never changed the brake fluid in any of my (road-going) vehicles earlier than after 2 years.

So, since everything points to a leak, I just wanted to know if this kind of issue is perhaps more common in my vehicle model, to make my search easier.

In my opinion, statements about the physical well-being of individual forum participants are not necessarily helpful.

Juergen wrote:

So, with all due respect; I'm not completely stupid!

No one has claimed that.

Quote:

Air or vapor bubbles in the braking system typically manifest as a very soft, spongy brake pedal. Additionally, the braking force on an affected wheel would be weaker, and this would be noticeable by a pulling sensation during braking.

"I wouldn't make a definitive statement about that; I know of other cases where it wasn't like that."

Quote:

The pedal initially offers normal resistance and then gradually gives way. Furthermore, this effect is the same whether the brakes are cold or hot, which, in turn, makes the vapor bubble theory unlikely.

Once steam bubbles get trapped in the system due to overheating, you might experience the problem even with cold brakes. It's definitely possible.

Quote:

Everyone who has ever read a repair manual has probably heard about the hygroscopic properties of brake fluid. However, in my 20 years of driving, I have never had any problems with it, even though I have never changed the brake fluid in any of my (road-going) vehicles earlier than after 2 years.

There's always a first time for everything .

Quote:

So, since everything points to a leak, I just wanted to know if this kind of issue is perhaps more common in my vehicle model, to make my search easier.

Normal ist das genauso häufig wie bei allen ander Fahrzeugen. So, rather rarely.

Please don't take this personally, but I always get a bad feeling when someone is "messing around" with the brakes (and describing it in that way). You also need to understand that other members might get headaches from such descriptions.

Okay, no offense, but I think your brakes are perfectly fine and there's nothing wrong with them.

'Let me quote myself.'

I'm having a similar problem with the brakes:

With the engine running, the pedal slowly depresses under very strong braking pressure.
If the engine isn't running, you can step on it as hard as you can, and it won't give way.

In my opinion, air in the system can be ruled out, as the brake fluid was changed two years ago, and the problem only recently started.

There are no visible leaks, brake fluid level is OK, brake performance is OK.

'If someone could just explain to me where in this text the word 'bastelei' (which roughly translates to 'tinkering' or 'DIY') is described!?'

Juergen wrote:

...If someone could now explain to me where in this text "bastelei" is described!?

Well...

Quote:

I would say that air in the system can be ruled out, because the brake fluid was changed 2 years ago, and the problem only recently started.

It doesn't sound like someone who has seriously dealt with the topic of brake fluid. You admitted and corrected that yourself later.

Quote:

At that time, I didn't know anything about the differences in quality when it came to brake fluid.

Let it go.

Braking is always such a sensitive topic, and I always feel a bit uncomfortable during discussions about it. I think Julian feels the same way.

That has nothing to do with you.

Hello,

I also have to add my two cents.

The whole thing is also very subjective. If you apply enough force to the brake pedal (i.e., with properly trained legs), you can actually push it almost to the floor (with the brake servo active, of course). In my old Passat, I could always do that (with a lot of leg strength, of course), even after I had replaced the brake lines and all the brake cylinders.

I think that, due to the material, some degree of stretching is possible in the brake hoses and lines. However, the only area that is safety-relevant is the one where complete wheel locking can be achieved. If the pedal is fully depressed and no brake fluid is entering through open areas (and there is no air), then the pedal force required to lock the wheels is probably already 500% above what is necessary -> so it doesn't matter for driving safety, because more force than what is needed to lock the wheels is not necessary .

Hi,

Perhaps I'm wrong now, but if the brake pedal doesn't give way when the engine is off, doesn't that sound less like air in the brake lines and more like a problem with the vacuum system or the brake booster?
I would simply go to a brake testing facility and examine the braking force.

Best regards, Sirecki.

Some problems solve themselves completely!

Situation:
Emergency braking on the highway from approximately 180 km/h, because it appears that trucks are being delivered in the Netherlands without rearview mirrors!

Since then, the braking system has been functioning normally again, meaning that the pedal only depresses slightly, even when pressed firmly.

Conclusion:
Definitely no air, steam, or any other kind of bubbles in the system, but it seems there's just dirt and/or rust where it shouldn't be!

Maybe brake fluid isn't as bad as its reputation suggests?!

Hi Jürgen,

Perhaps the swimming surfaces were simply stuck to the guides and became slightly loosened again due to the sudden braking...?
Have you checked yet?

Best regards, Rainer.

Hi Rainer,

I had already checked the suitability of the swimming saddles beforehand.

I noticed some slight scratches on the rear brake discs that I hadn't seen before.
It's possible that dirt had accumulated between the backing and the disc.

Best regards, Jürgen.

It's possible that dirt had accumulated between the back of the pad and the rotor.

Greetings, Jürgen.

or the ABS module is now bled...

CU Gremlin.

I'm having the same problem...
Braking performance is normal, but when the engine is running and the vehicle is stationary with moderate...
When you apply pressure to the brake pedal, it slowly depresses. The braking system feels smooth.
The brake fluid is one year old. I would actually rule out issues like solidification or the formation of air bubbles. Air in the lines usually manifests as a spongy brake pedal and uneven braking performance. However, that is not the case here.

Keep pumping the brake pedal until it becomes impossible to press it further, which in turn indicates...
It's not possible to close the air bubble.


So, what else could it be?
How do you properly bleed an ABS brake system?
Is there anything related to actuator diagnostics?

Thank you.
quadral

Hi,
Will you be able to fully depress the pedal in this way?
If so, that could indicate a leak in the master cylinder's seal.
If this issue doesn't occur when applying a lot of pedal force, that would also be an indication, as the seals would then provide a better seal.

The brake system of vehicles with ABS should be bled with the engine running; however, I don't believe that the symptom you described is related to air in the system.

If the pedal doesn't reach the floor, this can be normal. The vacuum pump for the brake servo continues to operate while you press the pedal, so the brake pressure gradually increases.

Regards,
Olli.