Nochmal : Unterdruck Bremsentuning | Posts 16+

Quote:

There's something in the works.

That's also why my question (which seems to have been overlooked) is:

Schraubi-Schlumpf wrote:

Perhaps it's only the BKV (battery control unit) that is defective. Did you perhaps have a lot of water in the reservoir before (which might be noticeable by water leaking into the passenger footwell)? It wouldn't be the first BKV that has been flooded.

Hi,

Quote:

Your calculation regarding area/braking force is interesting and sounds like a lot at first, but: With a fully flexed foot, an adult man can easily exert a pressure of 200 kg! (for example, to move furniture). However, in a car without ABS, it's not enough to prevent full braking, which means I believe there are other forces at play.

I somehow already noticed that something wasn't right with the calculation, because those 200 kg you mentioned seem to act on a lever arm, unlike the BKV (presumably another system), which means the resulting force is much higher.

While this doesn't advance the discussion, I'm curious: Where is the calculation error? Also, I'm not sure if you could still get the wheels to lock up without ABS if you were really putting 200 kg of force on the pedal.

Best regards,

January.

Dust...

Perhaps this information will be helpful to someone regarding the relationship between pedal pressure and vacuum pressure.
We once had a Nissan Micra with a CVT transmission and a severely undersized braking system. The necessary pedal pressure for a full stop (the car didn't have ABS) was extremely high when the transmission was in "D" mode. However, if you revved up the engine beforehand by shifting to "S" mode on the CVT, significantly less pedal force was required.

With a diesel engine, the speed (RPM) should not be affected by the vacuum pump, assuming it is functioning correctly.

With my Lupo TDI (equipped with a 256x20 Lucas braking system), I've noticed that when braking from very high speeds, you absolutely must not take your foot off the brake pedal for even a moment if the danger isn't completely gone. In the second after releasing the pedal, you experience almost no braking force and need to apply immense pressure to the pedal. This effect is also present, albeit slightly less pronounced, even with new brake fluid in both of my Lupos.
I can only think of insufficient vacuum or gas pockets on the surfaces.

Regards,

Olaf.

In your case, it seems the problem is either a very small or non-existent vacuum reservoir.

Okay, let's switch gears for a moment regarding this discussion – you can really tell how low the vacuum pressure is by the braking force. But don't forget that a maximum of -0.9 bar is usually possible. If the vacuum pump is working correctly, you'll get around -0.8 bar. If it's not functioning well, it will often still produce 0.6-0.7 bar, and the difference from 0.8 bar isn't that significant.

What surprises me is that even with almost identical braking systems...
There are significant differences in the performance of the brake booster.

As an example:
I've been driving an Audi A3 TDI with engine code AGR since 1997 for the past 7 years. The braking power is quite good.
However, a friend of mine drives an A3 TDI AGR from 1999, and the performance of her battery control unit is remarkably good.
Even with light pressure, it brakes very strongly. Same brakes, same vacuum pump, but a different brake control unit (BCU). More specifically, the alphabetical ending of the part number is different. The rest is identical, even visually.
My stepmother also drives an A3 TDI from 2002 with the less powerful common-rail engine.
which also has an identical braking system.
Only with her does it require more braking force applied by the foot.
BKV has yet another alphabetical ending.
It's likely that the BKV (a specific system or component) from year 1999 was too powerful, which made it difficult to brake precisely.
My plan is to obtain the part number for the BKV Bj99 and install it in my own vehicle.
And as I know VAG, this is likely to be compatible with other VAG vehicles as well.
Once I've completed the modifications, I will report on how it affects the braking performance.

Without wanting to offend anyone (or step on anyone's toes)...
Here, we need to have verifiable values.
= measured pedal force at a given braking force, e.g., for the front axle!
and this was with a reference vehicle that had the same load and braking system.
If that's the case, we can move on to the suggestions.
Otherwise, check the vacuum manifold for leaks by connecting a manometer and comparing any pressure loss or leakage after x brake applications.
Then there's the matter of building up leg muscle and overcoming the fear of slipping on a surface that is hopefully not too crowded.

teileklaus wrote:

Without wanting to step on anyone's toes (calculator)... Here, we need to have verifiable values. = measured pedal force at a given braking force, e.g., for the front axle! and this was with a reference vehicle that had the same load and braking system. If that's the case, we can move on to the suggestions. Otherwise, check the vacuum manifold for leaks by comparing the pressure drop and any loss or leakage after a certain number of brake applications. Then there's the muscle building in the leg and the reduction of fear associated with potentially slipping on a surface that is as free from traffic as possible.

Hi there,

It might also be useful (if possible) to read the hydraulic pressure; this could help rule out brake pads and rotors if the piston diameters are the same.

Aron wrote:

possibly... by reading the hydraulic pressure, one could already rule out pads and rotors when the piston diameters are the same.

That's right; it might be more complex, but then the translation ratio and the gain factor of the BKV (presumably a specific device or system) would be comparable.
However, the BKV can also be filtered using ET numbers.