Bremsproblem - Unterdruckpumpe defekt? | Posts 16+

So, before you accidentally disassemble yourselves...
'This actually happens to me even on country roads. For example, when turning at an intersection. I slow down, brake, then the traffic light turns red - I have to brake completely. I'm far away from the ABS activation range. I don't have a 'brake assist' system. Does that exist in newer models...?'
Regards,
Jens.

Hi,

My Ibiza does not have brake assist.

Of course, I haven't tried fully depressing the pedal (since it works even when the car is stationary... it shouldn't make a difference for the brakes other than the lack of heat generation and the protection of the rotors and pads). But I can imagine that the "lost" vacuum (well, more accurately: the air that flows back in) with about ten gentle pumps is roughly the same as with three full depresses.

Best regards,

Jan.

Interesting topic, as I first noticed this phenomenon on Sunday. And that was after approximately 100,000 kilometers driven myself. For the brake assist to noticeably decrease, I have to brake firmly about three times. I've already given a lot of thought to narrowing down the problem. I think a boost pressure gauge with a vacuum range would be helpful. It could be connected to the vacuum system. I wouldn't use my motorcycle synchronizer, as it displays a minimum of -0.6 bar.

But the problem is now solved, due to its design.

Regards, mcgregg.

I only notice this when the car is stationary (or rolling slowly). After pumping the brake pedal three times, it becomes firm.

@jensg
Have you checked the hose yet? To check it, gently bend it to the side; otherwise, it's hard to see. If there are any cracks, they'll be most visible then. If you find any cracks, the best thing to do is wrap some electrical tape tightly around it and replace the hose as soon as possible.

I completely agree with mcgregg. I've only just noticed it myself, although it's not very pronounced, but it's definitely there. In my case, compared to Roger, it's certainly due to the lack of a BAS (Brake Assist System). The way the BAS works inevitably creates a vacuum deficiency with closely spaced, repeated activations.
However, I don't think it's really a design flaw. It would be a flaw if the braking force could no longer be achieved at all, regardless of how much force is applied to the pedal.
My Golf is still under warranty, with 50,000 km on the odometer, and so far I haven't even noticed anything was wrong, which is probably also because I rarely brake hard repeatedly (or have to).

That's why I almost took the box apart at the beginning. I just wasn't used to it, and if you're often around the Frankfurter Kreuz, you'll encounter situations like that: You're driving along, and suddenly you see the traffic jam on the horizon. So you take your foot off the gas and brake early, so you don't have to slam on the brakes at the end. Then, 1 or 2 cars will cut in right in front of you because they absolutely have to use the gap that's formed, and suddenly you're at the limit with the braking. If you're used to it, it's manageable. But the first time is truly terrifying.

For every single thing, there are warning labels in the instruction manual. But not for things that are truly essential.

Hello Roger,
At 70,000 km with the AJM engine, and now almost 80,000 km with the ARRL engine, I've never noticed this before! I'll pay attention to it now.
Best regards,
Günther.

Hi,

I need to partially retract what I wrote earlier... this phenomenon can also be provoked in the ASV (Anti-Slip Valve). I repeatedly stomped on the pedal forcefully and quickly while the car was stationary, which led to the aforementioned stiffening of the pedal. However, I was still able to depress the pedal much further than is possible with the engine off and the vacuum reduced. Furthermore, three such simulated braking maneuvers were not enough... it was only noticeable after the fifth attempt, approximately.

Therefore, I consider it safe from a safety perspective, especially since the braking force is still likely to be significantly higher than it would be without power steering.

Best regards,

Jan.

I also experienced the problem you described.
First, I measured the vacuum pressure in the line. -> 0.2 bar vacuum pressure.
Vacuum measured in a similar vehicle -> 0.7 bar vacuum.
"There's a gasket set available for these pumps, but unfortunately, it didn't help in my case. I ended up having to buy a new pump. The vehicle was an Audi 80 1Z. The pump failed at approximately 290,000 km. Since installing the new pump, I haven't had any more problems."
Perhaps this will be helpful.

Hello,
So, it's definitely a problem with the vacuum pump!
Best regards,
Günther.

Okay, I think I've found the solution now. I've taken everything apart that was connected to it, and the hoses were actually okay (still, thanks for the tips).
Result: The boot of the vacuum pump is loose... It seems to be glued in and is now wobbling in the polystyrene. I'll try to seal it this weekend. But that's probably the problem. So, if you ever encounter something like this, check even the 'impossible' places...
Thank you for your active and interesting participation in this discussion.
Regards,
Jens.

Aha.

"Sounds interesting. Could you possibly illustrate that with a picture?"