Bremsentuning? | Posts 16+

Bertil wrote:

If you have too much free play in the HA (rear axle), then the VA (front axle) brake will engage before the HA brake. This means you lose valuable pedal travel and braking force. In the worst case, you won't even engage 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 become 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) parking brake lever adjustment by pulling the lever firmly, then keeping the brake engaged with the pedal, and releasing the parking brake.

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

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

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I'll have to look for that first... Found it... https://community.dieselschrauber.org/en/viewtopic.php?t=9982

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

Bertil wrote:

Back then I already tried to explain why that is.

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 even find it myself...
... but Goettmann describes exactly the problem that I'm referring to. By the way, I received the tip about the rear brakes from him many years ago .

ulf wrote:

... Zudem kann man ja eine (funktionierende) Handbremshebelnachstellung aktivieren, indem man den Hebel stramm zieht, dann die Bremse per Pedal geschlossen hält und die Handbremse wieder losläßt. SAlso, please translate the following text from German to English, keeping all http://www.kfz-tech.de/SchBremsN.htm exactly as they are. Provide ONLY the translation, no explanations.

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 also initially adjusts the engagement point of the service brake. The simultaneous shortening of the handbrake travel is a nice side effect and is mentioned here as the main reason for the adjustment, which is not entirely accurate.

In your opinion, would vehicles equipped with a hydraulic handbrake not require this mechanism?
Unfortunately, they have exactly the same feedback mechanisms, designed to maintain the balance between VA (ventricular assist) and HA (heart assist).

Wer sich noch an alte Fahrzeuge ohne automatische Nachstellung erinnern kann, der wird sich daran erinnern das es Fahzeuge gab die an allen Rädern Nachstllschrauben hatten. Diese musten so eingestellt werden das jedes Rad sich gerade so frei drehen lies. Das hatte mit der Handbremse nichts zu tun. Findige Konstrukteure sind dann darauf gekommen das eine Nachstellung nur auf einer Achse nötig ist, damit die Balance erhalten bleibt. Um

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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 pulled firmly, it locks the wheels, which is not something that happens easily on all cars.

I don't really need to adjust the handbrake when playing golf... I only need to adjust 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, essentially 'training' with it daily."

That's exactly what causes the surface to become glazed!
Deiner Beschreibung nach würde ich auf eine bescheidene Wirkung der hinteren Bremse tippen ... Brake testing machine.

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Despite this, I find the braking performance of my Polo with the "oversized 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. Exactly that promotes the glazing of the surfaces!

Hm, and how can we prevent it?

Without the regular braking, my brake discs will start to 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.
In my opinion, a disc brake on the rear axle is unfortunately not suitable for everyday "casual driving." The rear brakes tend to wear out faster than the front brakes. Unfortunately.

Exactly, 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 rather deteriorates. This is, of course, aside from exceptions like sports cars or heavy 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 to have four-disc brakes on production cars, back in the early 1960s.

Regarding automatic adjustment: A purely hydraulic disc brake does not require automatic adjustment. An adjustment mechanism is only needed for the handbrake mechanism if the handbrake is integrated. For drum brakes, there have been quite reliable automatic adjustment mechanisms available since around 1980, which usually function flawlessly 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 (for the time). When properly sized, they can provide quite decent deceleration. 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.

"Furthermore, drum brakes are simpler to control in ABS and ESP systems (because they don't have springs). Drums require a certain minimum pressure to engage and overcome the spring force. This makes a significant difference with a high control frequency. Also, vehicles with drum brakes on the rear tend to be at a disadvantage when driving downhill with frequent, light braking, because the rear brakes, due to the aforementioned spring, often don't engage, 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 reality for "average" drivers 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, you can achieve quite decent deceleration with them. The problem, then and now, 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 also 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. On the rear axle, however, as mentioned earlier, it can also exhibit disadvantages in everyday use.

BTW, not only does the engine appreciate an occasional highway drive at a brisk pace . Although my previous rear windshields were never as smooth and free of streaks as the front ones, they still lasted a long time without any issues; in the G III, they even lasted around 100,000 km without any repairs.

The best thing about the rear drums is the consistently clean 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" feel is probably somewhat intentional on the part of the manufacturer, as it makes it less noticeable when the ABS system is engaged.

Benno.

Benno wrote:

My son installed stainless steel brake lines on his Corrado, and since then, they have been working like anchors. Before that, he had rubber brake lines, as you described. This soft feel is probably somewhat intentional on the part of the manufacturer, as it makes it harder to feel the ABS engagement.

Hmm, in my opinion, we need to distinguish between a soft pressure point and the braking force at a specific pedal pressure.
"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 theory you mentioned about the stainless steel braided brake lines, when people would talk them up. However, it's definitely not true. In fact, as you press the brake pedal harder, the braking power increases, not the length of the hoses. It's precisely this expansion or cushioning of the pressure in the brake line that causes the brakes to feel "soft" or not "bite" properly.

Best regards,
Benno

You're absolutely right, Ulf!

Stainless steel braided brake hoses only improve the pedal feel; 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 press 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 pedal feel can result in a very slight improvement in braking distance, but that's more of a theoretical benefit. The main advantage of stainless steel braided hoses is the better feel you get with the brakes, their long lifespan (although I've also experienced a burst stainless steel hose – fortunately, it was on a test stand!), and their resistance to damage from rodents.

The self-adjustment mechanism on the rear brake is incorrect; it functions exactly the same way as on the front brakes, via the hole in the master cylinder through which fluid flows from the reservoir. The self-adjustment is only for the parking brake and eliminates the need to manually adjust the brake cable.

You can achieve better braking performance by using different rotors (e.g., slotted rotors from Zimmermann or grooved rotors like the ATE Powerdisc), especially with good performance 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, a great experience... 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 plates 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 plates, so the pads can now rattle a bit, which means they won't get stuck anymore. Of course, the rear brake now works 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 standard models. The standard hoses absorb some of the pressure through their "expansion," meaning that not 100% of the pressure is transmitted directly from the master cylinder to the calipers. This dampening effect also diminishes with age.

Of course, this only works with high-quality braided hoses, not with cheap "junk" hoses without any certifications, which are often produced in China and simply consist of rubber tubes wrapped in wire.

A higher force transfer to the brake pads will be achieved by installing a stainless steel braided brake line.
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 the pressure is no longer transmitted 100% from cylinder to cylinder. Sorry, but that is simply incorrect!

The pressure remains the same, but 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 with different stiffness. Let's use coil 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 be if you do the same with the stiffer spring? Certainly, also 10 kg, because the force of gravity cannot disappear. The only thing that changes is the spring's compression distance.

Subjectively, a stronger braking effect may be perceived 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 assess precisely with a 'popmeter.' A pressure sensor could be used to measure the pedal force and provide objective data.

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

I was thinking about the brake point... it's better achieved with this system because the pedal travel is shorter, meaning I have to pump less brake fluid into the lines.
Poorly phrased. My mistake.

Forenheini wrote:

... The self-adjustment mechanism on the rear brake is incorrect; it functions exactly the same way as on the front brakes, via the hole in the master cylinder through which fluid flows from the reservoir. The self-adjustment is only for the parking brake and eliminates the need to manually adjust the brake cable. ...

Then explain why cars with handbrakes that act on the front wheels (e.g., the Alfa Sud) had an automatic adjustment system 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 an automatic rear brake adjustment system. Some even have all-wheel drive parking brakes. In this case, an adjustment mechanism would be pointless.

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Or why vehicles with an electrically operated parking brake (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 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 unfortunate if there was still a centimeter of travel left to overcome and the driver was already at the bakery.

Best regards.
Dirk.