Bremsentuning? | Posts 64+

'So, I find the whole thing about the Zimmermann brakes really shocking. I was actually planning to buy some this year as a 'good' investment, but I probably won't now.'


I have previously had good experiences with Brembo MAX rotors combined with ATE pads. Has anyone else had a similar experience?

'The large sport brake system from the Ibiza Cupra should also fit the Polo 9N, Ulf... However, it will be quite tight when it comes to choosing wheels... especially in winter, because as far as I know, only 17-inch wheels will fit.'

Best regards, Alex.

Bertil wrote:

ulf wrote: ... What were your concerns about the old brake pads and rotors on the rear? Nothing! That's exactly what it was. I've experienced this several times where a faulty brake would start working properly again after replacing the rear brake components.

Hello,

I can fully confirm what Bertil wrote, based on my own experience. My rear brake pads still had about 4 mm of material left when I replaced them. The handbrake had no noticeable free play, but the braking force was very uneven; the lever "rattled" when pulled. However, one of the brake pad guides was completely seized and was restored, and new brake pads (genuine VW) were installed. With these new pads, the handbrake works smoothly again, and the responsiveness of the service brake has also become much more immediate. Also, the braking force is quickly applied even from high speeds, and it no longer decreases as much under heavy load.

I would only recommend paying close attention to the rear brake pads when there are issues with braking performance. If necessary, replace them; they don't cost a fortune. If I had noticed the effect sooner, I would have replaced them much earlier.

Roger wrote:

My rear brake pads still had about 4 mm of material left when I replaced them. The handbrake had no noticeable free play, but the braking force was very uneven, and the lever "rattled" when pulled. However, one of the brake pad guides was completely corroded and was restored, and new brake pads (original VW) were installed. With these new pads, not only does the handbrake work smoothly again, but the responsiveness of the service brake has also become much more immediate. And even at high speeds, the deceleration is quick and no longer diminishes as much under heavy load.. . .

Hi Roger,

My problem is mainly with the maximum possible braking force on the front axle, because I never reach the active ABS range. That means that with "ABS OFF" at a high speed, even with (initially) cold brakes, a complete brake lock-up would not even be possible.

Did you experience similar problems with the old brake pads? And after the change, was the maximum braking performance clearly better, in the sense that the ABS system started to engage again during full braking on dry roads?
If not, then your experience would at least partially be irrelevant to my problem .

My main problem is with the maximum possible braking force on the front axle, because I never reach the active ABS range, meaning that with 'ABS OFF' at a high speed, even with (initially) cold brakes, a complete brake lock-up would not even be possible.

Hello,

What was that about the maximum torque that can be transmitted by the tires?
AFAIK, this is speed-dependent, meaning that at higher wheel speeds, more torque can be transferred to the road.

If this is the case, Ulf is currently struggling with the compromise between high braking performance at high speeds and not excessively high braking force at low speeds, which would correspondingly improve braking performance in normal use.

You may have encountered one of the 'drawbacks' of your vehicle configuration here, as the 'basic' Polo is designed for lower speeds rather than high ones.
The corresponding sports models are, for example, equipped with a larger braking system.

The fact that brakes that are too large can lead to 'problems' in smaller vehicles was demonstrated, for example, by the old Seat Ibiza CUPRA, which was originally optimized for rally racing. It had the 280 x 20 brake system from the Golf GTI and therefore had a very aggressive braking feel, which also led to criticism regarding its usability on the road.

As long as Ulf's brakes don't tend to fade, he will probably have to accept that his brakes provide sufficient deceleration for normal driving.

Excuse me, with dimensions of 257x20, and with 130 horsepower, and an average curb weight of 1200 to 1300 kg, it is really not suitable for 'racing'.

I have previously had good experiences with Brembo MAX rotors combined with ATE pads. Has anyone else shared a similar experience with me?

I've read this many times before, and I'm going to install it in my colleagues' Polos.
Considering the friction values, I expect nothing different regarding braking performance. The only disadvantage is that the (standard) ATE pad achieves this high friction value with a relatively soft compound, which leads to higher wear and more pronounced contamination of the rims (fine dust alarm ).

Best regards, Jochen.

@jochen145:

Yes, that's right about the soft coatings; you could clean the rims every other day... As a small consolation, the coating is gentler on the brake discs.

Best regards, Alex.

Hi,

Quote:

The fact that brakes that are too large can lead to "problems" in smaller vehicles was demonstrated, for example, by the old Seat Ibiza CUPRA, which was originally optimized for rally racing. It had the 280 x 20 brake system from the Golf GTI and therefore had a very aggressive braking feel, which also led to criticism regarding its use on public roads.

Are you sure about that data? I actually have the same brake (280x22, with a wear limit of 20) in my ASV-Ibi (as standard). It brakes really well, especially in conjunction with the high front axle load, but it can become a bit unstable at high speeds for that very reason. During the only emergency braking I've done, from just under 200 km/h down to 120 km/h, I think the ABS kicked in somewhere around 140 km/h (at least at the front; you don't really notice it at the rear).

The Cupra R is listed with a 305x28 brake system from Brembo in the data I have access to. Are you perhaps referring to the previous model, the second-to-last Cupra up to 1999? In that case, the 280x22 brake system is indeed the largest listed.

It's really surprising that VW equips the 130 hp Polo with smaller brakes than the budget-friendly brand Seat used for the 110 hp Ibiza a few years prior.

Best regards,

Jan.

ulf wrote:

Did you experience similar problems with the old brake pads, and after the change, was the maximum braking performance clearly better, in the sense that the ABS started to activate again during full braking on dry pavement? If not, then your experience would at least partially not be relevant to my problem

.
Hello Ulf,

I had this exact problem for quite some time - actually, since I took delivery of the new car - despite having ESP with BAS. The BAS, after all, is supposed to provide a much more aggressive application of braking force in emergency braking situations, and thus the ABS should, in principle, bring the braking force into the regulated range much earlier should. However, with the old brake pads, this only worked properly at city speeds.

It has become significantly better now, even though the ABS system has only been activated once and briefly during highway driving. This happened at approximately 140 km/h when an idiot in the left lane ahead of me braked suddenly and completely unnecessarily. The Vectra C in front of me swerved to the left and right during the necessary braking, but luckily, I avoided that. However, the effect of my system was so unusually strong that a 45kg lead-acid battery, which was being transported lengthwise in the trunk near the back seat, hit the seat back quite hard and left a permanent impression .

Jan6K wrote:

Are you sure about that data? I actually have the same brake (280x22, 20 is the wear thickness) in my ASV-Ibi (as standard). It brakes really well, especially in conjunction with the high front axle load, but it can become a bit unstable at high speeds for that very reason. During the only emergency braking I've done, from just under 200 km/h down to 120 km/h, I think the ABS kicked in somewhere around 140 km/h (at least in the front; you don't really notice it in the rear). The Cupra R is listed with a 305x28 brake system from Brembo in the data I have access to. Are you perhaps referring to the previous model, the second-to-last Cupra up to 1999? In that case, the 280x22 brake system is indeed the largest listed. It's really surprising that VW equips the 130-horsepower Polo with smaller brakes than its budget-friendly subsidiary, Seat, used on the 110-horsepower Ibiza a few years prior. Best regards, Jan

Hello Jan,

Ulf had already written about his records:

ulf wrote:

My front windows, according to the documents, are 288 * 25 mm in size, which is slightly larger than those of the G4 Kombi.

Roger wrote:

ulf wrote: Did you experience similar problems with the old brake pads, and after the change, was the maximum braking performance clearly better, in the sense that the ABS started to engage again during full braking on dry pavement? I had this exact problem for quite some time - actually, since I took delivery of the new car - despite having ESP with BAS. The BAS, after all, is supposed to provide a much more aggressive braking force in emergency braking situations, and thus the ABS should, in principle, bring the braking force back into the regulated range much earlier should. However, with the old brake pads, this only worked properly at city speeds. It has become significantly better now.

Surprisingly, I will also try my hand at my HA brakes.

What I just can't wrap my head around is:
With a functioning brake system and the same full braking pedal force, the hydraulic system will always build up the same pressure, according to IMO. Pressure modulation only occurs when ABS is active.
As long as the ABS is not activated, I always have the same pressure in the wheel cylinders, and therefore the same clamping force of the pads.
Where (the heck) does the increased braking power on the front axle come from, if only the rear brake pads were replaced or adjusted?

Hello Ulf,

As mentioned earlier, there have already been several explanations. I also noticed a somewhat stepped response with the old pads, where you had to overcome a kind of intermediate stage before a firmer engagement was felt. It's possible that the stuck pad guide caused the pad to initially jam, before proper contact could be established with the remaining rear pads. Consequently, full pressure wasn't being applied at the front. Part of the braking force was being absorbed by the elastic deformation of the pad guide. That's my humble theory on the matter, at least.

Based on how the coating was applied, it wasn't properly lubricated from the factory. Therefore, premature failure is definitely possible. It's a known issue with this product line.

ulf wrote:

... My problem mainly lies with the maximum possible braking force on the front axle, because I never reach the active ABS range, meaning that at "ABS OFF" from a high speed, even with (initially) cold brakes, a complete brake lock-up would not even be possible. ...

The fact that you are not entering the ABS control range has (primarily) nothing to do with the VA (front) brakes!

How does the ABS control strategy work? When does the ABS activate?
The answer to that is very simple:
The ABS system only activates when the brake pressure exceeds a minimum value 'f' within a certain time period 't'. Otherwise, the ABS system remains (more or less) inactive.

Let's assume, for whatever reason, your brake pads are too far away from the brake discs. This increases the hydraulic travel, which in turn extends the time it takes to build up pressure in the braking system. In the worst-case scenario, it could even be so extreme that the ABS intervention threshold is no longer reached.
What reasons can cause an extended hydraulic travel? Well, one reason could be a warped brake disc. This pushes the brake pad too far back, thus extending the travel distance. You should be able to feel this, especially on the rear axle. A second reason could be the automatic adjustment of the rear brake pads. Rusted discs (which are common on many TDIs at the rear) can also push the pads back further than necessary after braking, resulting in the same symptom as above.
These are just two of many other reasons that could explain the types of errors you've reported.


By the way, I just demonstrated a trick to bypass the ABS. If you gradually increase the brake pressure, it's possible for the wheels to lock up anyway. However, newer ABS systems compensate for this with a brake assist feature.

Okay, with ABS, you need to initially apply the brakes very forcefully, and then gradually modulate the braking pressure. This way, you can utilize the full potential of the system.

Are you sure about that data? I actually have the exact same brake (280x22, 20 is the wear measurement) in my ASV-Ibi (as standard equipment).


Hi Jan, actually yes, but the first Cupra model would have had to be built before 1999 (with a 2.0L 150hp naturally aspirated engine from the Golf GTI), so it would be your predecessor model.

According to the data available to me, the Cupra R is listed with a 305x28 brake system from Brembo - or are you referring to the previous model, i.e., the second-to-last Cupra up to 1999? In that case, the 280x22 brake system is indeed the largest one listed.

Yes, that's correct. I just meant the predecessor .

It really surprises me that VW equips the 130-horsepower Polo with smaller brakes than the budget-friendly subsidiary Seat equipped the 110-horsepower Ibiza with a few years prior.

According to the documents, my front windows are 288 * 25 mm in size, which is slightly larger than those of the G4 Kombi.

Sorry, I somehow missed that.
Best regards, Jochen.

Bertil wrote:

The ABS only activates when the brake pressure exceeds a minimum value 'f' within a time period 't'. Otherwise, the ABS is (more or less) inactive.

Therefore, does the ABS react to a sensor value representing the "rate of pressure increase in the hydraulic circuit"?

Quote:

Let's assume, for the sake of argument, that your brake pads are (for whatever reason) too far away from the brake discs. This increases the hydraulic travel, and consequently, the time it takes to build up pressure in the braking system is extended. In the worst-case scenario, it could even be so extreme that the ABS intervention threshold is no longer reached.

Okay, let's say I were to perform a full-force emergency braking with "ABS OFF": Why, then, despite maximum pedal force, can't I get the tires to lock up, or at least make them squeal a little?
The pedal is still quite a distance from the floorboard, the brake booster seems to be working normally (IMO), and I don't consider my legs to be so weak that I can't apply the usual amount of force needed for a full brake application.

Quote:

What reasons can cause an extended hydraulic travel? Well, one reason could be a "warped" brake disc. This pushes the pad back too far, thus extending the travel. You should (at least on the front axle) be able to feel this. A second reason could be the automatic adjustment of the rear brake pads. Rusted discs (which are common on many TDIs at the rear) can also push the pads back further than necessary after braking. This produces the same symptom as above.

But if you have overcome the potentially extended pedal travel and are pressing the pedal with full force (well above the floor panel), shouldn't the full hydraulic pressure for emergency braking still be reaching the calipers?

And so, my question remains: Why doesn't the full hydraulic pressure of the emergency braking system in my Polo, even on a dry highway, cause either tire squealing or activate the ABS?
Oder erzeugt man etwa bei gleicher Pedalkraft "weiter unten" (aber noch über dem Bodenblech!) weniger Hydraulikdruck? If so, why?

I have also tried experiments with sudden, full braking, so that the pressure increase was definitely faster than with a retiree's full stop and a brand new braking system, even with a longer hydraulic travel: the result was always the same: no squealing, no ABS activation .

Hi,

Quote:

Sorry, I somehow missed that.. icon_redface.gif

It doesn't matter... I could have also checked Ulf's post. Now everything is right again...

@Bertil:

Quote:

By the way, I just demonstrated a trick to bypass the ABS. If you gradually increase the brake pressure, it's possible for the wheels to lock up even with the ABS engaged.

But only for a short time, right? Once they're really stopped, shouldn't the ABS release the brakes again in such a situation? Or am I missing something? I think the control system can distinguish this case (even if all 4 wheels stop at the same time) from the "car is stopped" case based on the rate at which the wheels' speeds are decreasing.

Of course, it's undeniable that it works more effectively during sudden braking.

Best regards,

Jan.

Quote:

The fact that you are not entering the ABS control range has (primarily) nothing to do with the VA brake! How does the ABS control strategy work? When does the ABS activate? The answer to that is quite simple: The ABS only activates when the brake pressure exceeds a minimum value of 'f' within a time period 't'. Otherwise, the ABS is (more or less) inactive.

I would say that the ABS activates when there is a certain amount of slippage between the road surface and the tires. If it activates too early, it only unnecessarily increases the braking distance.

If the braking performance of the rear axle of a vehicle is weakened for any reason, a portion of the total braking force is lost, which theoretically must then be compensated for by the front brakes.

Due to the further increased dynamic axle load shift towards the front axle, the forces transmitted between the road surface and the tires increase, which reduces overall wheel slip and, consequently, the ABS may intervene later or, depending on the grip level, not at all.

ulf wrote:

...Therefore, the ABS reacts to a sensor value representing the "rate of pressure increase in the hydraulic circuit"?

Yes, also.

Quote:

OK, so, let's say I were to perform a full-stop braking maneuver with "ABS OFF": Why, despite applying maximum pedal force, do the tires not lock up, or at least make a little squealing noise?

... So, at some point, it should squeak. That sounds quite strange.

Quote:

... But, if you've overcome the potentially extended pedal travel and are applying full force to the pedal (still well above the floorboard), shouldn't the full hydraulic pressure of the emergency brake still be reaching the calipers?

Yes, that's how it should be.

Quote:

And so, my question remains: Why does the full hydraulic pressure of the emergency braking system in my Polo, even on a dry highway, not cause the tires to squeal, nor activate the ABS?

On any road surface? So also on wet surfaces or snow/ice?

Quote:

Or does applying the same amount of pedal force generate less hydraulic pressure "lower down" (but still above the bottom bracket)?

No... the pressure should also be able to be generated "lower down" on the pedal stroke.

Quote:

By the way, I also tried sudden, full braking, so that the pressure increase was definitely faster than with a retiree's full stop and a brand new braking system, even with a longer hydraulic travel: the result was always the same: no squealing, no ABS activation

.
So, that sounds a bit strange. The brake really has a problem .

Jan6K wrote:

But only for a short time, right? Once they really stop, shouldn't the ABS release the brakes again in such a situation...?

Yes, but until then, the car has already traveled a certain distance without ABS intervention (even if it's only a few meters).

Quote:

I think that the control system can distinguish this case (even if all 4 wheels stop at the same time) from the "car is stopped" case by analyzing the rate of change of the wheel speeds...

Yes, that's correct. The ABS only regulates the speed down to 5 or 10 km/h. Below that speed, it is completely deactivated.