Bremsentuning? | Posts 16+

Bertil wrote:

If you have too much free play in the travel of the rear axle (HA), then the valve assembly (VA) brake will engage before the rear axle (HA). This results in a loss of valuable pedal travel and braking force. In the worst-case scenario, you might not be able to move the HA brake at all.

Hi Bertil,

That was already clear to me. But I mean that a parking brake that's too loose should be noticeable due to excessive free play in the handbrake lever (until the pads initially make contact with the disc).
Furthermore, you can activate a (working) handbrake lever adjustment by pulling the lever firmly, then keeping the brake engaged with the pedal, and releasing the handbrake.

It doesn't change anything for me either, but the lever travel isn't particularly long anyway (I've seen much worse).
I consider the handbrake performance to be normal: when you pull it firmly, the wheels lock up, which isn't "easy" to achieve in many other cars.
Therefore, I believe that glazed surfaces, etc., are not suitable, especially since I regularly use the parking brake with light braking maneuvers "for practice."

Despite this, I find the braking performance of my Polo with the "oversized" brake discs to be mediocre.

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I'll have to look for that first. . . Found ... /viewtopic.php?t=9982

No wonder I can't find anything with you as a search input: the explanation came from Goettmann, regarding

Bertil wrote:

Back then I already tried to explain why that is the case.

ulf wrote:

... No wonder I can't find anything with you as a search input: the explanation came from Goettmann, regarding Bertil wrote: . Back then, I already tried to explain why that is the case.

That's not my thread either... I can't find it myself either...
... but Goettmann describes exactly the problem that I'm referring to. By the way, I actually got the tip about the rear brakes from him many years ago.

ulf wrote:

... Furthermore, you can activate a (working) handbrake lever adjustment by pulling the lever firmly, then keeping the brake engaged with the pedal, and releasing the handbrake. See also http://www.kfz-tech.de/SchBremsN.htm

It's just a minor detail that the article omits certain things.

If the lining is now a little worn, the foot brake adjusts the handbrake.

Unfortunately, this process also initially adjusts the engagement point of the service brake. The simultaneous shortening of the handbrake travel distance is a nice side effect and is mentioned here as the main reason for the adjustment. That's not entirely correct.

In your opinion, would vehicles equipped with a hydraulic handbrake not require this mechanism?
Unfortunately, they have exactly the same imitation mechanisms. To strike a balance between VA (value-added) and HA (high availability).

"Those who remember older vehicles without automatic adjustment will recall that some vehicles had adjustment screws on all wheels. These had to be adjusted so that each wheel could rotate freely. This had nothing to do with the handbrake. Ingenious designers then came up with the idea that adjustment only needed to be made on one axle to maintain balance." Around.

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It doesn't change anything for me either, but the lever travel isn't particularly long anyway (I've seen much worse). I consider the handbrake performance to be normal: when you pull it firmly, the wheels lock up, which isn't "easy" to achieve in many other cars.

I don't need to use a :wink:cheater bar for the handbrake when playing golf... I only need it for the drum brakes on my Jetta.

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Therefore, I believe that glazed surfaces, etc., are not suitable, especially since I regularly use the parking brake with light braking maneuvers "for practice."

That's exactly what causes the surface to become glazed!
Based on your description, I would suspect that the rear brake is having a limited effect... Brake testing machine.

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Despite this, I find the braking performance of my Polo with the "oversized" brake discs to be mediocre.

Okay, so my G4 has been braking really well again since I replaced the rear brake pads and rotors (at 60,000 km).

Bertil wrote:

Quote: Therefore, glazed coatings, etc., are excluded in my opinion, especially since I keep the handbrake engaged with light braking "in training" every day. That's exactly what promotes the glazing of the surfaces!

Hm, and how can we prevent it?

Without the regular braking, my brake discs will rust from the outer edge (which I experienced with my Golf 3), and with strong handbrake applications, the rear axle tends to lock up .

ulf wrote:

... Hm, and how can we prevent it?

Probably not at all.
A disc brake on the rear axle is, in my opinion, unfortunately not suitable for everyday "casual driving." The rear brakes tend to wear out faster than the front brakes. Unfortunately.

Absolutely, Bertil!

I've been saying this for 20 years! Problems with rear disc brakes almost always occur due to insufficient use, and it's only gotten worse with the introduction of the handbrake that acts on the hydraulic piston. The material doesn't wear out anymore; it just deteriorates. Apart from exceptions like sports cars or large sedans.

Why are they being installed everywhere today? Because the costs aren't higher, the heat dissipation is significantly better, and the maintenance is simpler. Also, it's a matter of prestige. I believe Alfa Romeo and Jaguar were among the first manufacturers to offer four-disc brakes as standard equipment on production cars, back in the early 1960s.

"Regarding automatic adjustment: A purely hydraulic disc brake does not require automatic adjustment. An automatic adjustment mechanism is only necessary for the handbrake mechanism if the handbrake is integrated." Regarding drum brakes, there have been quite effective automatic adjustment mechanisms available since around 1980, which generally function reliably for many years.

And speaking of braking performance, let me also mention the highly advanced drum brakes of the legendary Auto Union or Porsche racing cars (which were, of course, state-of-the-art for their time). When properly sized, they can provide quite decent braking power. The problem, then and now, is always the cooling.

Best regards, Rudi.

isar12 wrote:

Why are they being installed everywhere today? Because the costs are not higher, the heat dissipation is significantly better, and the maintenance is simpler.

Also, because they are easier to control in ABS and ESP systems (because they don't have springs), drum brakes require a certain minimum pressure to engage and overcome the spring force. This makes a significant difference when using a high control frequency. Furthermore, vehicles with drum brakes on the rear axle are at a disadvantage when driving downhill with frequent, light braking, because the rear brakes, due to the aforementioned spring, often don't engage at all, while the front brakes have to absorb all the heat energy. I don't want to discuss whether this driving style is appropriate. However, it often reflects the typical braking behavior of the average driver in mountainous areas.

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And speaking of braking performance, let me also point out the (for the time) highly advanced drum brakes of the legendary Auto Union or Porsche racing cars. With appropriate sizing, they can provide quite decent deceleration. The problem, and it still is, is always the cooling...

The drum brake is much more susceptible to fading because, with reasonable effort, i.e., without aluminum cooling fins like those used by Auto-Union or air ducts, it is not only difficult to cool, but primarily because its geometry causes the friction surface to become conical due to thermal expansion, resulting in only a small fraction of the lining area making contact. Furthermore, it is significantly more sensitive to uneven pressure. Due to these many advantages, the disc brake has made a very rapid advance – at least on the front axle. At the rear axle, however, it can also exhibit disadvantages in everyday use, as previously described.

BTW, it's not just the engine that appreciates an occasional highway drive at a really brisk pace . My rear windshields have never been as smooth and free of ridges as the front ones, but they have always lasted a long time without any issues; in fact, on the G III, they lasted around 100,000 km without any repairs.

The best thing about the rear drums is the consistently verschandeln rims .

Hello,
If I'm interpreting the problems correctly, please check your brake hoses.
A person presses firmly on the brake pedal, and you can feel the "bulging" of the hoses. When the brake pressure causes the fluid to inflate the hoses, it's time to replace them. This isn't necessarily just about age; the quality also plays a significant role. My son installed stainless steel braided brake hoses in his Corrado, and they've been working perfectly ever since. Before that, he had rubber brake hoses, like the ones you described. This soft handling is likely also intentionally designed by the manufacturer, as it makes the ABS system less noticeable.

Benno.

Benno wrote:

My son installed stainless steel brake lines on his Corrado, and since then, they have been working like a charm. Before that, he had rubber brake lines, just like the ones you described. This soft feel is probably also intentionally designed by the manufacturer, as you don't feel the ABS regulation as much.

Hmm, here, it's important to distinguish between a soft pressure point and the braking force at a specific pedal force.
"Using stainless steel braided hoses will likely result in a firmer pedal feel, as the need to pre-inflate the hoses is largely eliminated."

But, for example, if you apply 300 N of force to the pedal, the braking performance shouldn't change, in my opinion. The only difference would be that you would need to depress the pedal less with stainless steel braided hoses compared to the stock hoses...

Hello Ulf,

I used to believe the same thing you do, when people would talk about the benefits of braided brake lines. However, that's definitely not true. The braking power increases with the pressure on the brake pedal, not the length of the hoses. Because it is precisely this build-up or dampening of pressure in the brake line that causes the brake to not "bite" properly.

Best regards,
Benno

You're absolutely right, Ulf!

Stainless steel braided brake hoses only improve the responsiveness, but they don't change the brake pressure itself. You just have to press the pedal further. The only exception is if the expansion of the 'normal' hoses is so great that you can push the pedal all the way to the floor, in which case the pressure would be limited. However, this is usually not the case, because standard hoses aren't that bad! The improved responsiveness can lead to a very slight improvement in braking distance, but that's more of a theoretical benefit. 'An important advantage of stainless steel braided brake lines is the improved brake feel they provide, and that they are very durable (although I've also experienced a stainless steel braided line bursting - fortunately, it was on a test stand!). They are also very resistant to damage from rodents.'

The information that the follow-up mechanism on the rear brake is for the service brake is incorrect; it functions exactly the same as on the front brake, using the hole in the master cylinder through which fluid flows from the reservoir. The adjustment is only for the handbrake and saves you the trouble of adjusting the brake cable.

You can achieve better braking performance with different rotors (e.g., slotted rotors from Zimmermann, or grooved rotors like the ATE Powerdisc), especially when combined with good sport brake pads. In my Fabia, I also have the 256mm rotors, which, in my opinion, might not be very generous considering the 1.3-ton curb weight, but so far, I haven't had any reason to complain about the braking performance. Recently, a brake pad got stuck on one of the rear calipers, which was, as always, great... You don't really have anything else to do over New Year's. The fact that this happened was almost inevitable because the small metal pieces that are on the brake caliper brackets, which guide the brake pads, hold the pads too tightly, and that's only to minimize noise... I've now removed the lower metal plates, which means the pads are now rattling a bit, and therefore can't be tightened properly. Of course, the rear brake now works much, much better than before, which was to be expected.

Okay, Benno... I don't understand that, maybe you didn't explain it clearly.
Logically and observably, when using stainless steel braided brake lines, there's a more defined pedal feel (assuming everything else is in order). This is due to the higher pressure resistance of these hoses compared to the stock lines. The stock lines absorb some of the pressure through their "expansion," which means that not 100% of the pressure is transmitted directly from the master cylinder to the calipers. A weakening of this transmission also occurs with age.

Of course, this only works with high-quality stainless steel braided hoses, not with cheap, unregulated hoses produced in China that are simply made of rubber tubes wrapped in wire.

A higher braking force will be transmitted to the brake pads when a stainless steel braided brake line is installed.
It is already clear that these [add-ons] do not necessarily increase braking performance, because they cannot replace an undersized brake system.

These absorb a portion of the pressure through their 'expansion,' which means that the pressure is no longer distributed 100% evenly from cylinder to cylinder. A weakening of this transmission also occurs with age. Sorry, but that is simply incorrect!

The pressure remains the same, only the volume changes differently because the spring characteristics of the stainless steel flexible pipes are different. You can easily test this yourself: take a 10 kg weight, a scale, and two springs of different hardness. Let's use compression springs. Place the first (softer) spring on the scale and zero the scale. Then place the weight on it. What will the reading be? Of course, 10 kg. What will the reading likely be if you do the same thing with the harder spring? Certainly also 10 kg, because the force of gravity cannot disappear. The only thing that changes is the path, the suspension travel.

Subjectively, the brakes may feel more powerful because the same braking force is achieved with less pedal travel. People often associate braking force with pedal travel rather than pedal force, which is difficult to accurately measure with a device like a 'popmeter.' A pressure sensor used to measure pedal force would provide a technical basis for that measurement.

Sure... I probably also expressed it completely wrong, my mistake.

I was thinking about the brake point... it's better achieved with a system that originates from there, as the pedal travel is shorter, meaning I have to pump less brake fluid into the lines.
Very vaguely expressed. My mistake.

Forenheini wrote:

... The information that the follow-up mechanism on the rear brake is for the service brake is incorrect; it functions exactly the same as on the front brake, using the hole in the master cylinder through which fluid flows from the reservoir. The adjustment is only for the handbrake and saves you the trouble of adjusting the brake cable. ...

Then explain why some cars have handbrakes that affect the front wheels (e.g., The Alfasud had an automatic adjustment feature for the rear brakes.
Or why vehicles with electrically operated parking brakes (where there are no cables and the distance is irrelevant... the system always applies the pads with a defined force) also have automatic rear axle adjustment. Some of them even have all-wheel-drive parking brakes. A follow-up mechanism would therefore be pointless in this case.

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Or why vehicles with electrically operated parking brakes (where there are no cables and the distance doesn't matter... the system always applies the pads with a defined force) also have an automatic rear axle alignment adjustment

.

I can imagine that this could ensure a consistent braking time, as these systems, due to the force required, likely operate relatively slowly by leveraging leverage. It would be annoying if there was still one more centimeter to go and the driver was already lining up at the bakery:-).

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

"Dirk"