Bremsentuning? | Posts 80+

Quote:

Quote: By the way, I also tried sudden, full braking maneuvers, so that the pressure increase was definitely faster than a gentle, full brake application by an elderly person, even with a brand new braking system. The result was always the same: no squealing, no ABS activation. Well, that sounds a bit strange. The brakes are really messed up.

If that is really the case, I would first replace the brake pads/shoes all around .

Bertil wrote:

ulf wrote: And so, my question remains: Why doesn't the full hydraulic braking pressure in my Polo on a dry highway cause either tire squealing or activate the ABS? On every road surface? So, even in wet conditions or on snow/ice?

With reduced grip and sufficient pedal pressure, the ABS works normally, meaning it keeps the wheels (seemingly) from locking up by allowing them to rotate just before locking, the pedal vibrates, and the pump hums.

Quote:

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

. . . but I think it's perfectly normal, as long as it's not about the maximum. Delay until the blocking threshold is reached on a dry track is acceptable.
The brakes were also not flagged as an issue during the vehicle inspection.

Do you have any suggestions on where I could start my search?

Could an ABS malfunction limit the braking pressure on a dry surface significantly before wheel lock-up occurs, without the brake pedal vibrating? Okay, I would then try pulling the main fuse for the pump and attempting the anti-lock braking system again (in a completely electrically inactive ABS system, the speedometer signal is missing because the transmission sensor has been omitted).

What are some indicators that can help identify glazed surfaces when dismantling them?

In a "full emergency braking" situation, either the ABS system must engage, or the wheels will lock up.
"Definitely getting winter tires."
or you have a can lid brake, brake fade, air in the system, Qualifire slicks, or seized calipers/pistons/frame.
"But with a 280 disc, I can't imagine that being normal."
I believe that the SBB (Swiss Federal Railways) are most likely finished, because they are exhausted.

Burnt-out SBB (Swiss Federal Railways) brake pads: You can stick your screwdriver into the soft material and easily scrape it off, just like charcoal.
"Verglaste" refers to a surface that is "glass-hard."

.. and I don't think my legs are so weak that I can't generate enough pedal force for a full stop.

So, I once used a braking reaction simulator to measure the force with which I press the pedal during an emergency braking situation.

The device indicated 75 kg as the pedal pressure.

My Leon works with 225 tires on 8' rims, but the ABS control range is achieved with a 10' brake vacuum booster.
Which tire brand do you use? Here as well, there are significant differences in traction.

One more thing:
Ulf, did you depress the clutch pedal during your attempts?
When the engine is not connected to the wheels, it still has enough power that the tires will not lock up.

Best regards, Jochen.

Jochen_145 wrote:

Which tire brand do you use? Here as well, there are also significant differences in traction.

During the tests, the tires used were the original equipment (OE) SR: 195/55 R 15 Firestone Firehawk.

Quote:

Ulf, did you press the clutch during your attempts? If the clutch is not engaged, the engine still has enough power that the tires will not lock up.

. . but that's probably only if it's resisting stalling at a speed below the low-speed limit?
Since I conducted the tests above 150 km/h, I was in 5th or 6th gear. Okay, and even with the low-rev limiter, it's not delivering much torque to the wheels - but during braking, the engine was definitely always above the low-rev limit, so it was in a state of torque interruption.

Okay, without auxiliary brakes, both the vehicle and the motor's rotation need to be slowed down, but in higher gears, the difference in RPM per km/h is relatively small. Therefore, "that small amount of inertia from the rotating motor components" shouldn't overwhelm a 288 mm brake, especially if it's used in addition to braking the vehicle itself?

It is my opinion that it would be highly problematic if reaching the blocking threshold meant reaching the maximum value. Braking is only possible if the driver, during an emergency braking situation, is still calm enough to remember to disengage the clutch.

ulf wrote:

. . . but I think it feels perfectly normal, as long as it's not about the maximum. Delay until the blocking threshold is reached on a dry track is acceptable.

It feels normal, but it's not normal!

Quote:

The brakes were also not flagged as an issue during the vehicle inspection.

Yes, something like that has happened to me twice. After the technical inspection, I drove home and bumped into the wall in the garage... Once, a brake hose burst... the second time, it was a seal in the hydraulic brake booster. That's all about the vehicle inspection.

Quote:

Do you have any suggestions on where I could start my search?

Okay... I would start by replacing the brake pads and rotors all around. Quite expensive, but probably unavoidable.
I'm also leaning towards "glazing."

Quote:

Could an ABS malfunction limit the braking pressure on a dry surface significantly before wheel lock-up occurs, without the brake pedal vibrating?

Okay, I'm ready. Please provide the German text you want me to translate. Normally, I would say no.

Quote:

Then I would try pulling the main fuse for the pump and attempting another ABS activation (with a completely power-less ABS, the speed signal is missing because the transmission sensor has been omitted).

Hopefully, your brakes are not assisted by a hydraulic pump... (but that's rather rare these days).


Okay, one more thing:
How old is your brake fluid?

Bertil wrote:

I also suspect glazing.

I just tried to find possible causes for glazing on the coating, but I haven't really become any wiser - except for indications of severe overheating.
Since I try to avoid braking as much as possible and let the car coast whenever I can, I'm wondering how my brake pads could still develop a glazed surface – and, more importantly, how can you tell if they're glazed when they're removed?

The approximately 4 test braking maneuvers were not always brought to a complete stop, but at best reached a speed of -80 km/h. However, even the first test was unsatisfactory, as the Polo had never experienced true "glazing" of the brake pads before. Could the pads have already been glazed at that point? If so, what user errors were involved, or how can I avoid them in the future?

Quote:

Hopefully, your brake is not assisted by the hydraulic pump... (but that's rather rare these days).

Then it would probably make a regular buzzing sound before the ABS kicks in? -> No, there's no buzzing sound.

Quote:

How old is your brake fluid?

It was about 2 years old during the tests, but now it's almost 4 years old. I'll be getting it changed soon...

During the tests, the tires used were the factory-fitted SR: 195/55 R 15 Firestone Firehawk.
Hmm, there isn't a tire here known for having a particularly soft compound and therefore offering a lot of grip.

. . but probably only if it resists stalling at low engine speeds?
However, the motor has a certain amount of inertia, so it takes a while to lose its speed, and it continues to drive the wheels for a while longer.

I wouldn't bet right now that I can get the tires to lock up without pressing the clutch.
I haven't used rev-matching (blip the throttle) when downshifting in my old Fiesta yet. Did I release the clutch too quickly? If so, the engine's speed dictated the wheel speed, causing them to either squeal or slip.

It wasn't until I used racing brake pads (Ferodo ID 451) that I was able to effectively reduce the engine speed using the brakes.

OK, without the torque converter, both the vehicle and the motor rotation need to be slowed down, but in higher gears, the difference in rpm per km/h is relatively small, so 'that little bit of inertia of the rotating motor masses' probably shouldn't overwhelm a 288 mm brake, especially if it's used to decelerate the motor in addition to the vehicle?

However, it further hinders the braking process.

Incidentally, it would be, in my opinion, highly problematic if reaching the blocking limit = max. Braking is only possible if the driver, during an emergency braking situation, is still calm enough to remember to disengage the clutch.

No, I don't see it that way, because that's how it's taught...


I've been searching online a bit, but I haven't found what I'm looking for yet.
Perhaps someone among you knows more about this.

Given the maximum braking power, shouldn't the process here follow a similar principle as with the engine?

So, the formula would be: Power = Torque * RPM * Constant.

The maximum torque transmitted by the wheels must remain constant.

According to this, there should be a correlation between the wheel speed and the maximum transmittable braking power.

At low wheel speeds, the wheel is more likely to lock up because the maximum transmittable torque is exceeded more quickly than at high wheel speeds.

However, the maximum braking performance is not speed-dependent.

@Ulf

Can you potentially lock up the wheels at low speeds?

Best regards, Jochen.

ulf wrote:

... I've just been trying to find possible causes for glazing defects, but I haven't really become any wiser – except for indications of severe overheating.

Curing through aging.
This is actually a normal part of the process. The constant cycle of heating and cooling makes the surface harder, which allows it to become glazed more quickly. Then, you won't need to use as much heat for the glazing process. It's hard to say exactly how far that issue might be affecting your materials.

Quote:

Since I try to avoid braking as much as possible and let the car coast whenever I can, I'm wondering how my brake pads could still be glazing over.

Well, not really... but depending on the type of tires, that can definitely happen. I had the same issue with the original tires on my Golf. They weren't worn out, but they were just ineffective. But it's definitely not like what you're describing here.
"Bedding in" new brake pads is crucial for their longevity and performance.

Quote:

and, most importantly, how can you identify it from the (finished) surface?

Here's the translation:

"That part had already been written by Klaus."
Burnt-out SBB brake pads: you can stick the screwdriver into the soft material and easily scrape it off, like charcoal.
Verglaste are "glass-hard" on the surface.

Quote:

The approximately 4 test braking maneuvers were never brought to a complete stop, but at best reached a speed of around -80 km/h. However, even the first test was unsatisfactory, as the Polo had never experienced "glow braking" before. Could the surfaces have already been glazed at that point?

I would actually say no. Nevertheless, it seems that's the case.

Quote:

If so, what user errors were involved, or how can I avoid them in the future? . .

"Properly" bedding in new brake pads and rotors. The line between that and "clumping together again" is very thin.

EDIT:
I once had an instruction manual from a brake pad manufacturer:
Bedding in new brake pads:

Proper bedding-in of new brake pads is essential for their long lifespan and for ensuring the brakes function correctly. If possible, do not install new brake rotors on your vehicle during the break-in period of the new brake pads.

If a different type of brake pad material was previously used on the old brake rotors, it is recommended to verschandeln the rotors with sandpaper. The brake pads must fit freely and without binding within the brake caliper.

After starting, brake several times at a slower speed to create an 80- to 90-percent contact area between the pads and the brake rotors. After a few brakes at a higher speed, the pads should be cooled down during normal driving. Typically, the surface can be loaded .

Hi!
Okay, something completely different: Did you somehow manage to get grease on the windows while working on the suspension? So, either the brake pad guides are too heavily lubricated, or it's the wheel studs, or something else entirely!


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

"Dirk"

Bertil wrote:

ulf wrote: Since I don't brake aggressively, but rather let the car coast as often as possible, I wonder how my brake pads could still develop glazing - Well, not really... but depending on the type of tires, that can definitely happen. I had the same issue with the original tires on my Golf. They weren't worn out, but they were just ineffective. But it's certainly not like you're describing it here.

Which types of vehicles did you "successfully" replace the original brake pads on?

Perhaps my description sounds a bit too dramatic. The fact that I can't activate the ABS on dry pavement is true. However, during full braking, I don't get the feeling that it's doing significantly too little. I plan to soon test the braking distance from a real speed of 100 km/h and compare it to average car braking distances, which are around 38-40 meters(?).

Quote:

"Proper" bedding-in of new pads and rotors. The line between that and "clumping together again" is very thin. EDIT: I once had an instruction manual from a brake pad manufacturer: . . .

Thank you, that will certainly help some of the readers as well

Quote:

Did you somehow manage to get grease on the brake discs while working on the suspension?! Like, did you over-grease the brake pad guides or the wheel bolts, or something like that?!

To prevent rust, I always apply a little grease/oil to the wheel hubs and bolts during the seasonal wheel change (not a thick layer "just in case"), and I'm very careful to make sure nothing gets on the friction surfaces, but basically, I can only rule out your point 99%. If that stuff, thanks to capillary action, were to spread over unexpected distances, you might be right that small amounts could end up on the outside of the brake discs...

ulf wrote:

What types of vehicles have you successfully replaced the original brake pads on?

I can't say for sure, but I think it was LUCAS.

Quote:

Perhaps my description also sounds a bit too dramatic. The fact is that I can't activate the ABS on dry pavement.

Just a thought.
You are performing this test with an empty vehicle. Your permissible gross vehicle weight is likely to be 300-400 kg higher. You can also tow an unbraked trailer with a weight of 600-750kg.
If a brake reacts like that under these conditions, I would say: Overload.
However, in your case (i.e., with an empty vehicle), the brakes would need to be able to "overbrake" the wheels slightly, and the ABS would need to intervene. The maximum braking performance is always based on the maximum load condition.
At least during the initial braking, the ABS should need to modulate the brakes for 1-2 seconds. Also, even on dry surfaces.

Quote:

However, I don't feel like the braking power is significantly lacking during emergency braking situations.

I even believe you.
Unfortunately, you tend to get used to such a "weak" brake.

By the way, the initial braking force and its effect are the most important factors for a short braking distance. So, the energy that is dissipated in the first third of the braking process is the most important.

Okay, I just finished disassembling the VA-SBB (factory equipment). They are Ferodo 4307: is Ferodo generally known for providing moderate grip?

I noticed no perceptible signs of grease or oil on the friction surfaces, and I was able to slightly indent the lining support plates with a screwdriver when applying more pressure.
However, I still used a medium-grit sanding block to sand the entire surface, which resulted in noticeable sanding dust (indicating a dry surface, meaning no oil or grease in the material). This should have removed any potential thin layer of glazing... ?

During installation, I thoroughly cleaned the track guides and applied copper grease to them.

Let's see how the brakes perform on the next trip...

@Ulf

What is the free play of your handbrake lever?

Bertil wrote:

@Ulf What is the free play of your handbrake lever?

7 cm until the pads engage, measured right at the front of the release button.

Quote:

Let's see how the brakes perform on the next trip...

Same as before, after slowing down.

Build something new; everything else is just nitpicking.
"Hey, does the brake start making noises as soon as the pads get hot?"

If so, then all the more so.

It's probably thanks to your generally cautious driving style that you haven't damaged the brake discs with the Ferodo pads.

Regarding Lucas Klötzen products, I have installed them a total of 3 times because there were no other options available. And I have had to return them (due to defects) exactly 3 times.