Bremsentuning? | Posts 32+

brezelmann01 wrote:

... because these systems, due to the required power, certainly operate relatively slowly. ...

<0.5 seconds for full braking force.
I would call that anything but slow (at least for a manual braking system).

Hello!

I've also never heard that the mechanical simulation is meant to replicate the function of the service brake. How does it work, for example, in Porsche cars? In those, the service brake acts on a disc at the rear, while the parking brake acts on a drum.
Six months ago, I replaced the brake pads on the rear of a Volvo 850. It has the same system as a Porsche. With that system, there's absolutely no adjustment needed!

...
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.
...

Okay, explain why cars with handbrakes that act on the front wheels (like the Alfa Sud) had an automatic adjustment system for the rear brakes.
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 adjustment system. Some of them even have all-wheel drive parking brakes. In this case, an adjustment mechanism would therefore be pointless.
I won't explain that because I don't know the systems well enough. Besides, what you're constantly doing is like comparing apples and oranges. Why don't you try explaining it the other way around: explain why the service brake needs the adjustment, but please do it thoroughly and clearly, and ideally cover all the variations. Then we'll have a basis for discussion; I'm happy to change my mind.

Forenheini wrote:

... explain why the service brake needs to be readjusted. ...

I already did that above.
That's how it was explained to me, and if that's not correct, I have no problem with it.
My observation aligns with the described problem, where the rear brake often plays a significant role in the overall performance of a braking system.

P.S. By the way, the idea about the brake hoses isn't bad either. It can work wonders. Unfortunately, the approved stainless steel braided hoses are quite expensive.

Hello,

The automatic brake adjustment system only serves to reduce maintenance costs. I remember my early days of car ownership. Back then, a visit to the workshop every 3,000 km was normal. During that visit, the oil would be changed, and the brakes would be adjusted. My son, in addition to his Corrado, also owns a VW Sülzer from 1979. With this car, the brake shoes also need to be adjusted after approximately 3,000 km. However, there is no actual improvement in the poor braking performance, even if one subjectively feels that there is.

Benno.

Ulf mentioned brake tuning at the beginning, so let's assume the brakes are in good condition and the adjustment is working correctly.

Theoretically, one can...
1. increase the coefficient of friction between the brake pad and the disc.
2. increase the contact pressure of the pads.
3. increase the effective diameter (of the disc or drum).

Regarding point 1, you can use parts from racing applications, provided they are street legal. However, in my experience, the really high-performance parts (which are usually not street legal) tend to perform significantly worse than the standard parts when they are cold.

Here are some possibilities for option 2:
- Larger pistons in the wheel brake cylinders.
- smaller pistons in the main brake cylinders.
- Change the pedal ratio.
- Modify the brake booster (increase vacuum or use a larger one).
while the latter is not associated with a longer pedal stroke as the only measure.

Regarding item 3, there are also parts from the sports sector, or often from more powerful models within the same group of companies.

I already mentioned the difference between our two vehicles. Others report similar observations in the opposite direction. I suspect that this might be related to the effect of the brake booster. If someone knows whether the vacuum pumps are the same for the AFN and ALE engines, I can try it out this weekend. (Even if they're not the same, I'll probably still try it.)

Then there's the brake booster itself. Does anyone know if VW/Audi uses different models?

Best regards, Rudi.

I already did that above. If you're referring to: The fact that the mentioned article conveniently omits certain things is just a minor detail.

If the brake pads are slightly worn, the foot brake automatically adjusts the handbrake.

Unfortunately, this also initially adjusts the engagement point of the service brake. The fact that this simultaneously shortens the travel of the handbrake is a nice side effect and is mentioned here as the main reason for the adjustment. That's not entirely correct. Then, take a closer look at the matter, and especially from the other side; only then will things make sense. Due to the play in the thread of the adjustment mechanism, the brake piston can move independently up to the adjustment limit, which is also essential because otherwise there would be no clearance for bleeding! The issue of the engagement point is not an argument; without mechanical adjustment, it would still be ensured by the follow-up hole in the master cylinder. Only by combining the handbrake adjustment in the caliper does the adjustment essentially define an 'engagement point,' but only if it's done correctly; then it will be where it should be in the hydraulic system.

In my opinion, an adjustment for hydraulic brakes is only necessary when the maximum piston stroke is less than the wear allowance of the pads, but even in this case, the compensation hole ensures that the piston's travel always remains the same. The problem is that the piston will eventually fall out of the cylinder , which is not ideal. The adjustment on the rear disc brake with integrated handbrake, as is common with VW for example, only serves the handbrake; the fact that certain things result from this is only a consequence, but not a necessity.

My observation aligns with the described problem, where the rear brakes are often the limiting factor for the overall effectiveness of a braking system. I agree. Often, the argument is made that the significantly higher braking power at the front means the rear brakes are not important. However, that is unfortunately not the case, because maximum braking force is only achieved when both axles brake at their maximum. Therefore, the proper function of the rear brakes is also important. A malfunctioning rear brake is only compensated for by the fact that the rear brakes simply have to brake harder, which is usually not the problem, because the deceleration is usually so weak that it doesn't become noticeable. This (weak brakes) is also the reason why the (disc) brakes on the rear are prone to corrosion, because they simply don't receive enough load to clean themselves properly.

P.S. By the way, the idea about the brake hoses isn't bad either. It works wonders. Unfortunately, the approved stainless steel braided hoses are quite expensive.} 100-150 Euros or so, I don't find that too expensive... You can either install/bleed them yourself or have it done for a reasonable price during the inspection, if the brake fluid is being changed anyway. It's not a big deal.

@Ulf

Does the Polo have a brake assist system? In my Golf 4, there's a noticeable difference in braking performance whether the system engages during emergency braking or not.

Forenheini wrote:

... The issue with the engagement point isn't an argument, because even without mechanical adjustment, it would still be ensured by the bleed hole in the master cylinder. It's only when the handbrake adjustment in the caliper is combined with this that the adjustment effectively defines an "engagement point," but only if it's done correctly, in which case it will be where it should be within the hydraulic system.

What's the point of automatically adjusting the rear disc brakes without a handbrake being engaged, especially if the handbrake is only on the rear axle?
Then this construction can only be used for the point of application.
I'm planning to work on the car this spring. It belongs to a friend who's into motorsports. By the way, it even has brake discs attached to the transmission.

Quote:

In my opinion, a compensation mechanism for hydraulic brakes is only necessary when the maximum piston stroke is less than the wear allowance of the pads. However, even in this case, the compensation hole ensures that the piston's travel remains constant.

The piston definitely can't be that short.

Quote:

The (weak brakes) are also the reason why the (disc) brakes on the rear tend to get clogged, because they simply don't receive enough stress to clean themselves properly.

I already mentioned this above. I don't think self-buffing is very effective in hardcore mode (although I don't have major problems with it).
Even in my rally car, I have drum brakes in the rear.

Quote:

... 100-150 Oirohs, or something like that, I don't think that's really that expensive...

So, for a functioning brake, that wouldn't be too expensive for me, but many people start complaining when it costs 150 euros...

joegolf wrote:

I'm actually curious about the Polo and whether it has a brake assist system. Does it have one? In my 4th generation Golf, there's a very noticeable difference whether the brake assist engages during full braking or not.

The manual doesn't mention a brake assist system, and I haven't noticed any "phenomena" so far that might indicate it's present.
According to that, the 9N model probably doesn't have a brake assist system.

ulf wrote:

Therefore, the 9N probably does not have a brake assist system.

Only available with ESP in Germany.

Hi,
I also experienced that effect with the Golf 3, where the brake pads looked good but had poor braking performance due to being hardened.
In my opinion, the primary change is in the braking performance, specifically the responsiveness during moderate braking. Depending on the type of brake force distribution system, the pressure on the rear brakes is reduced during full braking to prevent the rear axle from locking up and causing a loss of control. My G1 performed well on the track. At the same time, the overall stability is increased during moderate, sustained loads, such as a descent with insufficient engine braking, because the rear axle can contribute more effectively to braking in this situation compared to a fixed distribution system.

Are we always talking about the same thing? Of course, drum brakes require mechanical adjustment, whether manual or automatic. With disc brakes, this adjustment happens more or less automatically.
I'm not sure how a excessive clearance in the brake system could affect braking performance. Aside from friction factors, no braking force can be generated at the front axle as long as the rear brake pads are not engaged. Or are there EBV (Electronic Brakeforce Distribution) systems or mechanical brake force limiters that would be affected?

Do braided stainless steel hoses actually last longer, or do we just not see the fine cracks that develop inside?

Then explain why cars whose handbrake acts on the front axle (e.g., Alfasud) had an automatic adjustment of the rear brake.
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 adjustment mechanism. Some of them even have all-wheel drive parking brakes. A readjustment mechanism would therefore be pointless. As I said... I don't know the systems well enough to say anything about them without knowing more. Google didn't help me much with the brake on the Alfa Sud either, it just confirmed what we already know: the parking brake acts on the front wheels, and the brake is located on the inside of the front. It would be important to know the design in more detail...

Do stainless steel braided hoses actually last longer, or do you just not see the fine cracks inside? Of course, stainless steel braided hoses don't last indefinitely either, but they usually last for the entire lifespan of a car. Unlike regular hoses, there are no cracks in the outer rubber.

hiho

Without having read much about this, I've also often had problems with braking in my 6n (approximately 1 ton, ~110 horsepower, 256x20, 14-inch brakes) (wow, what's that glowing in the rim ). Well, I first installed slotted Zimmermann discs and Ferodo DS Performance brake pads, which already helped, and the response was excellent. After 20,000 km, however, one of the front brake discs cracked (fortunately at 20 km/h). According to Zimmermann, I somehow caused them to rust too much. Then I installed heat-treated slotted discs from Sandtler, and those were also great.

And what helped the most with the excessively high temperature was the rims.

Sure, here's the translation:

'Here are some pictures of the Zimmermann brake disc after 2 years or 20,000 km.'

http://people.freenet.de/officekeil/PICT0001.JPG
http://people.freenet.de/officekeil/PICT0005.JPG
http://people.freenet.de/officekeil/PICT0004.JPG

Oh dear, that's quite unfortunate. Silver lining, though.

So, my all-around tires are still looking great, and they've now been driven for about 35,000 kilometers.

How exactly should one understand the issue of rust? What influence do I have on it, other than leaving the vehicle in the mud for a year? And even then, it's highly questionable. So, something like this should never cause everyday rust.

It's a shame, I thought Zimmermann was competent.

hiho

Well, don't ask me.

Here are two emails from Zimmermann:

Hello Mr. Keil,

... how can this possibly happen???

With only 30,000 km of mileage, the brake surfaces are, frankly, in a rather 'degraded' condition. The brake surfaces are heavily pitted, which means they have been repeatedly subjected to sudden cooling or quenching while in a hot braking state. This can lead to stress cracks and changes in the material structure, which can compromise the mechanical strength.

The triggering moment for the complete failure of the brake caliper was evidently a brake caliper that was blocked on one side. This meant that the brake caliper was subjected to a lateral force acting on only one side. This type of tension-compression load is extremely unfavorable for the brittle cast material and subsequently leads to what is known as a brittle or stress fracture! Unfortunately, your photos do not show the inner brake pad surface, which should show significantly fewer signs of pad contact.

Best regards,

Achim Kerstan.
Leiter QS u. B.Eng. (Bachelor of Engineering)

and number 2:

Hello Mr. Keil,

Your uninformed comments prompt me to respond once again.

A caliper failure is always the result of a one-sided tensile-compressive stress (see my first answer); if the caliper was still functioning two days prior, then, for whatever reason, it doesn't necessarily have to be the case at the time of the failure! ... Or are you yourself sitting as an involved observer while driving, inside or on the brake caliper, and did you personally verify the functionality of all components just at the moment of the failure?

The combination of heat and moisture, coupled with drastic cyclical stress, leads to complete corrosion of cast iron with flake graphite, also known as gray cast iron. This is especially true when it occurs repeatedly, as appears to be the case in your situation (to put it mildly, the BS components look like they were mounted on an amphibious vehicle!).
Cast iron, even in its alloyed forms, consists almost entirely of iron. Therefore, from a purely chemical perspective, it is logical that cast iron will corrode if exposed to the appropriate weather conditions and operating environments. The manufacturer cannot be held responsible for these conditions.

Original equipment (OE) brake pads often have a corresponding level of corrosion protection, which can delay or minimize rusting, but never completely prevent it. However, the price for this is often double, or even triple, the price of ZIMMERMANN products.

Since you haven't specified which product you're referring to, I can't tell you what material your BS is made of.

Best regards,
Achim Kerstan.
Leiter QS u. B.Eng. (Bachelor of Engineering)


and the saddles definitely weren't damaged because I was able to push them back in by simply pulling them outwards.