Brake tuning?

Hello,

My Polo 9N comes with slightly larger brakes from the factory compared to versions with up to 74 kW, which means that at least 15-inch wheels must be used (minimum size for versions up to 74 kW: 14 inches).

Now, one might think that these things would provide particularly good delay values. However, if you're on dry pavement and accelerating at a higher speed (so that you don't come to a complete stop), the ABS doesn't even engage.
To even get the ABS to engage, you really have to stomp on the brakes with full force, just like I imagine a panic braking situation would be, for example, when you're driving at 160 km/h behind a bend on the highway and suddenly come upon the end of a traffic jam.
Conversely, this means that with less force applied to the brake pedal (due to lack of physical strength or an initial misjudgment of a dangerous situation), braking power is wasted because even the narrow 195-size tires aren't reaching their grip limit!

My 96kW "naked" Polo is certainly lighter than most of the 74kW TDI Polos, which come with the usual "comfort" features (the catalog lists an equipment-related unladen weight range of approximately 160 kg, but the minimum weight of the 96kW TDI is only about 40 kg higher than the 74kW model).
When I try to imagine the maximum braking performance of an average-weight 74kW TDI with even smaller brakes, for example at a speed of 160 km/h, compared to my car, I almost feel sick .

What is VW thinking, installing such poorly-looking brakes?
Could the factory-specified combination of disc and pads (friction coefficient?) be so unfavorable that high braking forces cannot be generated?
Could the effect then be achieved, for example, by...? Can installing different brake pads improve performance (without voiding the operating license)?
Or is it possible that the geometry (friction surfaces and diameter) of the brakes simply doesn't allow for higher braking performance, so that even the large brakes of the 9N model are, in terms of weight, simply undersized, regardless of the friction material used?

Oh yes: the friction surfaces of my brakes are neither rusty, nor oily, nor excessively worn.
Tread depth is okay, mileage is approximately 20,000 km.

Hi,

@Ulf:

Quote:

But if you're on a dry surface and accelerating at a higher speed (so that you don't come to a complete stop), the ABS doesn't even engage. To even get the ABS to engage, even just a little bit, you really have to stomp on it with full force

.
I've noticed that too. Specifically, this issue has occurred in multiple Volkswagen Golf IV Variant models (5 units), as well as in 3 Ford Focus models. (To be more precise, this applies to all Golf Variant and Focus models that I have tested so far.)
When braking from 180 km/h by continuously pressing the brake pedal, there comes a point where you're applying maximum force to the brake pedal, and the ABS still doesn't engage.
Anyway, at first I typed "brake fluid," then "discs and pads," and now I'm typing "at a loss."
You can do this 20 times in a row, and it always yields the same result. What's strange is that you can hear a slight squealing of the tires and also see a very faint black mark on the asphalt. Nevertheless, you don't hear or feel anything from the ABS at all! Furthermore, I'm surprised that it's the same with the Focus. So, I can't really believe it's a design flaw. On the other hand: From a security perspective, it's _FATAL_.

Regards,
Sure, here is the translation of the text from German to English:

"Micha"

I know that problem, but in a different way:
On our Audi A4 (1996, 110hp TDI), you have to slam on the brakes like an ox, especially when it's wet. In the case of the Golf Variant (1998, 90hp TDI), the ABS system activates even with less braking force.

My girlfriend usually drives the Audi, but when she occasionally drives the Golf, the passengers, including the driver, are thrown forward into their seatbelts every time she brakes. I've already installed sport brake pads on the front axle of the Audi, but the improvement in terms of braking force is hardly noticeable. I've considered replacing my loved one's front brake calipers with ones that have larger pistons, but that would mess with the brake balance and isn't the right approach.

I've also considered the vacuum pump from the brake booster. When I have the chance, I'll try fitting the one from a Golf into my Audi to see if it works. A larger master cylinder could also be considered, if one were available.

It can't be possible that the cheaper Golf brakes better than the Audi.

Best regards, Rudi.

Hi,

I'm not sure if the performance of a brake system should really be judged based on whether it allows you to engage the ABS at 180 km/h. If they manage to get close to the limit before slipping, that's actually okay, maybe even better.

On the Ibi, the front ABS only activates on dry roads at slower speeds (under 50 km/h) when braking very hard. However, the perceived braking power is still enormous, which I believe is likely due to the very unbalanced weight distribution. Other smaller TDI engines (like the one in Ulf's Polo...) probably have the exact same problem.

Specifically, in the Ibi model, 66% of the mass is located in the front, and 33% is located in the back. When braking hard on the highway, the car tends to swerve quite a bit... basically, the rear wheels can hardly contribute any braking force at that point, so the ABS kicks in, and you might not even notice it much.

In the roughly similarly built Polo 6N, which was about 7 cm shorter and had 2 cm less wheelbase, and with the AEX engine (which was, well, probably 200 kilograms or more lighter), the handling felt noticeably more balanced and stable. However, I never used it to brake from speeds of 170+ km/h, as it wasn't capable of going that fast.

Best regards,

Jan.

We've been through something similar before, although not exactly the same. "Back then, I also complained about the harsh braking performance of my Golf, which, as Ulf and others describe, can slightly increase your heart rate, especially at very high speeds, combined with the somewhat unstable suspension."
At that time, I was able to acquire a V6 brake system at a relatively low price. It has 312mm discs, which means 16 inches. That wouldn't be a problem. However, the brake caliper is the same as the one I have. The difference is that the brake disc has a larger surface area. Having once had the opportunity to drive a V6, in this case to brake it, I was also disappointed (okay, it's not really comparable, I admit, it's just too heavy a thing).

I then, and I mean, Rainer was among those who suggested it, decided to go with Zimmermann brakes all around. I "returned" the V6 parts from egedöns and have been very happy with the braking performance ever since. Unfortunately, I can't provide any specific measurements, but some smaller tests gave me more confidence. I hope this isn't just a subjective opinion.

...
After replacing the rear brake discs and pads, I was finally satisfied with the braking performance of my G4.
"It's great, and even with a light touch, you can easily access the cheap ABS plastic for installation."

Jan6K wrote:

Other smaller TDI engines (like Ulf's Polo...) probably have the exact same problem. Specifically, in the Ibi model, 66% of the mass is located in the front, and 33% is located in the back. When braking sharply on the highway, the car swerves quite a bit...

Hi Jan,

When I accelerate hard in my Polo at high highway speeds, there's no noticeable swaying or instability – at least, I haven't experienced anything like that so far.
Perhaps I was too preoccupied with being startled that the ABS wasn't activating.

Quote:

If they manage to get right up to the point where the tires start to slip, that's actually okay, maybe even better.

I don't see it that way: how do you know how much more delay is possible before locking up, and therefore how much is being wasted(!), if neither the ABS kicks in, nor do you apply enough pedal pressure to cause a brief lock-up (and then slightly release)?

Bertil wrote:

After I replaced the rear brake discs and brake pads, I was finally satisfied with the braking performance of my G4. It's really appealing, and even with a light tap, you can get the scrap ABS ready for installation.

Hi Bertil,

What were your concerns about the old brake pads and rotors on the rear?

And what is the size of your front windshields?

ulf wrote:

... What were your concerns about the old brake pads and rotors on the rear?

Nothing!
That's it, then. I have experienced several times that a faulty brake, after replacing the rear brake components, starts working properly again.

Quote:

And what is the size of your front windshields?

280 x 22 (15")
All G4 TDI station wagons have a 5-bolt pattern with 15" brakes.

Hi,

Quote:

When I accelerate hard in my Polo at high highway speeds, there's no swaying or instability – at least, I haven't noticed anything like that so far.

It could also be related to the tires... back then, they were probably low-quality tires from Firehawk (or whatever they were called). I haven't experienced that with the Continental tires, but I also haven't had to do any emergency braking at 200 km/h with them. "Definitely, I can clearly feel that the rear end is getting very light (figuratively speaking...)."

Best regards,

Jan.

Bertil wrote:

ulf wrote: ... What were your concerns about the old brake pads and rotors on the rear? Nothing! That's it, then. I have experienced several times that a faulty brake, after replacing the rear brake components, starts working properly again. Bitte gib den Text an, den du übersetzt haben möchtest. All G4 TDI station wagons have 5 bolt holes with 15" brakes.

Well, this is another interesting thing... Do you have any explanation for why your car brakes better now, especially at the front, where most of the energy is "dissipated"?

Could it possibly be related to a misadjustment of the handbrake lever mechanism (e.g., the cable lever not being fully engaged when the brake is released), or is the adjustment somehow different after the change, other than the retracted piston?

Or are the rear brakes the only ones that work better with the new parts?
That wouldn't be very useful for my Polo: My rear axle, which is hardly stressed, only provides a minimal braking effect, even at the point where it would normally lock up (tested using the handbrake).

My vo. According to the documents, the window panes are 288 x 25 mm in size, which is slightly larger than those in the G4 Kombi.

ulf wrote:

My vo. According to the documents, the

discs are 288 * 25 mm in size, which is slightly larger than those in the G4 Kombi.
Same here. However, I don't feel that the system struggles with the braking power itself, but rather that the vacuum pump isn't providing enough assistance. This is supported by the fact that with a similarly sized system in the GIII GTI 2.0, you could practically come to a standstill just by dropping anchor. When I was driving the G III (with a weight of 1,110 kg according to the registration) with 4 people, the weight was approximately equivalent to a G IV (1,301 kg) with only the driver inside. However, the GIII offered significantly better braking performance, despite only having 205-size tires fitted (compared to the G IV, which had 225-size tires).

Since you mentioned the 14" brake system, our 9N has FS-III brakes with 256x22 rotors in the front and drum brakes with 200x40 in the rear, despite the optional ESP (Electronic Stability Program). Last summer, we drove the Polo with 2 people and approximately 80 kg of luggage on the highway, going downhill and hitting the speed limiter (190 km/h on the speedometer). As I then needed to apply full braking power to avoid Murphy, I could see my previous life flashing before my eyes ...

ulf wrote:

... Well, this is another interesting thing... Do you have any explanation for why your car brakes better now, especially at the front, where most of the energy is "dissipated"?

If you don't bring the ABS (Anti-lock Braking System) into operation when braking, you're wasting a significant amount of braking power.
In addition, the HA (handbrake) is the only braking system in a vehicle that automatically adjusts for wear. If this mechanism is not functioning correctly, the entire braking system will become unbalanced and can lose up to 30% of its total braking power.
Those who use the search function will discover that we've already had this discussion here before. Back then, I already tried to explain why that is the case.

Quote:

Could it possibly be related to a misadjustment of the handbrake lever mechanism (e.g., the cable lever not being fully engaged when the brake is released), or is the adjustment somehow different after the change than it was before?

No.

Quote:

, besides the stuck piston?

... and what is the purpose of this mechanism?
Then you have your explanation!

Quote:

Or are the rear brakes the only ones that work better with the new parts?

That explains itself.

Quote:

That wouldn't be very useful for my Polo: My rear axle, which is hardly stressed, only provides a minimal braking effect, even at the point where it would normally lock up (tested using the handbrake).

That was exactly my problem. After replacing the (actually good) brake pads and rotors, the braking feel was significantly different after the break-in period (200 km). If I pull the handbrake now, it's like I'm shooting a bolt through the rims.

Quote:

My vo. According to the documents, the

discs are 288 * 25 mm in size, which is slightly larger than those in the G4 Kombi.
I just double-checked. I also have 288*25... According to AKTE, the G4 has 280mm and 288mm brake rotors available.

Roger wrote:

Last summer, we drove the Polo with 2 people and approximately 80 kg of luggage on the highway, going downhill and reaching the speed limit (190 km/h on the speedometer). As I then needed to apply full braking power to avoid Murphy, I could see my previous life flashing before my eyes...

Oops .
What saved you?

Bertil wrote:

In addition, the HA, as the only braking system component in a vehicle, has an adjustment mechanism to compensate for wear. If this mechanism is not functioning correctly, the entire braking system will become unbalanced and can lose up to 30% of its total braking power. Those who use the search function will discover that we've already had this discussion here before. Back then, I already tried to explain why that is the case.

Hi Bertil,

I can't find anything about it - I'm probably using the wrong search terms.
Do you have another link?

Quote:

other than the inserted piston? ... and what is the purpose of this mechanism? Then you have your explanation!

I think it's related to the parking brake adjustment mechanism.

But what this has to do with the hydraulic braking force is not clear to me...

ulf wrote:

... I can't find anything about it - I'm probably using the wrong search terms. Do you have another link?

I'll have to look for it first.

Quote:

I think it's related to the parking brake adjustment mechanism.

No, that's not the case (at least not primarily)!

Quote:

But what this has to do with the hydraulic braking force, I don't understand.

Ulf... just think about it!

If you have too much free play in the pedal travel before the rear brake engages, the front brake will activate before the rear brake. This results in a loss of valuable pedal travel and braking force. In the worst-case scenario, you might not be able to engage the parking brake at all.
The adjustment mechanism on the HA (likely referring to a vehicle's rear axle) is designed to synchronize the engagement points of the brakes. If the wheels lock up, you lose a significant amount of braking power.
It is important that a braking system responds evenly across the entire braking range. This is the purpose of the follow-up mechanism.
Unfortunately, this mechanism doesn't compensate for frosted or cloudy (foggy) surfaces. The only solution is to replace them. That's the whole problem.

Bertil wrote:

I'll have to look for it first.

Found... /viewtopic.php?t=9982

@isar/ Rudi

Quote:

In the case of the Golf Variant (98 model, 90PS TDI), the ABS system activates even with less force applied.

Then it's a Golf 3, with drum brakes in the rear and a really terrible brake balance.
I also command a ship like that, and I've come to the following conclusion:

He only brakes in the front.
This creates such immense force on the front tires that they want to grip and stop every time.

My ABS is working overtime, and the tractor is contemplating whether it really needs to slow down.

Modern cars tighten the seatbelt much more noticeably before ABS or similar systems even kick in.

m;