Sticking Disc Brakes: Causes and Solutions (Solution)

When the brakes fail to engage properly during operation and become excessively hot, the following steps will help in identifying the cause:
- Check if the wheel is difficult to turn even when stationary and cool. If so, check if the brake booster ventilation is working (if not, this would affect more or less all wheels, not just individual ones). Often, there is a small filter here that becomes clogged with dirt and debris, reducing its permeability.
- Yes: Remove the wheel, open the bleed nipple on the brake caliper. If the wheel now turns easily, there is residual pressure in the brake fluid, for example, due to a swollen brake hose, a faulty master cylinder, or valve problems in the ABS module.
- If the brake disc is still difficult to turn even with the bleed valve open, either the brake pads are stuck in their guides or the brake piston is not retracting properly after releasing the brake pedal. The latter is often caused by a damaged dust boot on the piston, leading to rust and corrosion. Also, old rubber seals on the brake piston itself can hinder its retraction.

With this approach, you avoid aimless and expensive part replacements based on guesswork; instead, potential causes are systematically ruled out.

Good luck!

Are there any pictures of the BKV (air conditioning unit) available? Where is it located? How is it removed? Typically, the BKV is only accessible after removing various components both inside and outside, unlike in the Golf 1 where it's located in the engine compartment.
hg
Herbert.

Hi!

I have never had any problems with the BKV ventilation system.
"But during a braking training session, they once said..."
Normally, it goes into the vehicle's interior.
Where the connecting rod from the pedal mechanism connects to the blower valve.
That's where the ventilation should be.

There should be a small filter there, made of foam, felt, or something similar.


But, as I mentioned before, I've never had any problems with that.

Brake hoses should be replaced once every 10 years.
and once a frozen BKV (Building Permit Application).
In the A4, it's located in the water tank.
The drains tend to get clogged because of that strange rubber stopper that you're supposed to remove.
Yes, I was at my neighbor's place.
The BKV was soaking in the water for months, slowly absorbing it.
The neighbor had parked his car outside, intended to drive to work early, but then he lost control and rolled across the street, coming to a stop in the grass.
That wasn't very funny. He simply didn't stand a chance.

As the temperature rose during the day, the brake started working again.

When he told me that, and that the car was making some kind of gurgling sound, I also had a feeling and was able to find it right away.

Herbert wrote:

Are there any pictures of the BKV (blower valve) from BKV Belüftung? Where exactly is it installed? How is it removed? The BKV is usually only accessible after removing all sorts of parts inside and outside, unlike in the Golf 1 where it's in the engine compartment. hg Herbert

Hello Herbert,

I don't know where the bleed valve for the brake caliper is located on the Audi A3 8PA. I stopped troubleshooting when the brake was still stuck, even with the bleed valve open, but the pads and guides were moving freely.
I found something online that conveys the same meaning as what Steffen wrote.

Best regards, Rainer.

Hi,
The principle of the pneumatic brake booster is well described here:
https://www.kfz-tech.de/Biblio/Hydraulische_Bremse/Bremskraftverst.htm

Okay, a defect in the master cylinder will affect all wheel brakes, not just one.
A restricted airflow caused by the pedals (e.g., a clogged filter) delays the servo effect due to the reduced pressure difference, eventually leading to its failure.
The same applies to limited vacuum on the HBZ side.
The BKV (vacuum brake booster) can only apply the brakes independently if the pressure on the brake pedal is not released, which can happen due to a leak in the BKV's valve. This effect should disappear after a certain period of engine idling, as the vacuum and, consequently, the pressure difference within the BKV will decrease. The same applies after repeatedly pressing the brake pedal with the engine idling.
hg
Herbert.
hg
Herbert.