Brake Problems: Common Issues & Solutions (18-04-2004, 17:38)

Hello everyone.

I'm having the following problem with my Golf 3 TDI, manufactured in February 1994, with a mileage of 214,000 km.
During the ride, I'm hearing a very annoying whistling sound. It's kind of like a sharp 'ss' sound.
It's not constantly audible, but it's annoying.

'When this squealing noise occurs, it disappears if I press the brake pedal very lightly. However, it reappears after a short drive.'

About 3 months ago, I could hear a similar whistling sound while the car was stationary, specifically when I pressed the brake pedal (although it was a very short, high-pitched sound).

It's coming from the front, but I can't tell if it's from the engine compartment or the brake pads.

The brake discs and pads are in good condition. I cleaned everything and lubricated the moving parts with copper grease.
The rear drum brakes are also in good condition.

I am grateful for any advice.

bird of prey

Bird of prey wrote:

When this squealing occurs, and I press the brake pedal very lightly, the noise disappears. However, after a short drive, it reappears. About 3 months ago, I could hear a similar whistling sound while the car was stationary, specifically when I pressed the brake pedal. (It was a very short whistling sound)

Hi,

Since you can influence the noise by pressing the brake pedal, I'm guessing there's a small leak somewhere in the power brake booster area.
When braking, the vacuum is "consumed" and then "replenished," and each time, the pressure relationships between the brake vacuum system and the outside world change.

I haven't been able to produce that whistling sound while standing still for several weeks now.
It occurs while driving.
And if I brake gently, it goes away. But it keeps coming back.

Is there a way I can test the brake booster?

I also lean towards Ulf's theory about a leak in the vacuum supply system of the BKV (Brake Control Unit). It's not contradictory that the noise doesn't occur when the vehicle is stationary, because the engine is usually running at idle speed in that situation. At idle speed, the vacuum pump can only provide a small amount of vacuum, and therefore can only generate a lower vacuum pressure. Due to your leak, only a very small vacuum pressure can be built up at idle speed, so that the hissing sound is barely noticeable.
During operation, the speed and thus the pumping capacity of the vacuum pump are higher, which increases the pressure difference to the surroundings. At this point, the hissing sound becomes loud enough to be noticeable.

Regards,
Alex.